Category 6™

Two Pacific-sized disasters: the Samoan tsunami and Typhoon Ketsana

By: JeffMasters, 1:29 PM GMT on September 30, 2009

The Pacific spawned another huge natural disaster yesterday, when a magnitude 8.0 - 8.3 earthquake near Samoa generated a tsunami that devastated portions of American Samoa and neighboring islands. While the ocean surface was only displaced about three inches by the force of the earthquake near its epicenter, the rupture occurred near the 10,000 meter-deep Tonga-Kermadec Trench, along a swath 200 - 300 km long. A column of water miles deep and 200 - 300 km long accelerated downward by the force of gravity (or lifted upward by crustal motion) by three inches represents an massive amount of energy released into the ocean. The quake was able to generate a 1.5-foot tsunami on the Hawaiian island of Oahu 2,700 miles away, and a 0.6-foot tsunami on the Oregon coast, over 5,000 miles away.

Portlight.org is considering adopting an American Samoa family to help out in the wake of this huge disaster. They would like some feedback from their contributors on whether to go ahead with this idea, so stop by the Portlight.org blog to join the discussion.

Typhoon Ketsana
Typhoon Ketsana has finally dissipated, but not before bringing record flooding to Vietnam, two days after creating recording flooding and chaos in the capital of the Philippines, Manila. Ketsana made landfall Tuesday morning in Vietnam between Hue and Da Nang as a Category 2 typhoon with 105 mph winds. The storm dumped up to 20 inches of rain on Vietnam, according to satellite estimates. Some rivers in central Vietnam rose above the record flood heights recorded in an epic 1964 flood. In all, Ketsana has been responsible for 41 deaths in Vietnam and 11 in neighboring Cambodia, with many more missing. At least 350,000 people are homeless in Vietnam, joining the 380,000 left homeless in the Philippines from the storm.


Figure 1. NASA MODIS satellite image of Ketsana approaching Vietnam on Tuesday, September 28, 2009. Image credit: NASA Earth Observatory.

The death toll in the Philippines from Ketsana has stabilized at 246, with another 38 missing. Residents of the islands need to keep a wary eye on Typhoon Parma, which is expected to intensify into a major typhoon and brush the northern Philippine island of Luzon on Saturday and Sunday.

Quietest September in the Atlantic since 1997
Well, it's the end of September, and what is traditionally the busiest month in the Atlantic was unusually quiet. We had only two named storms this September, the first time since 1997 we've had less than three September named storms. There were only 6.75 days in September with a named storm, which ranks as the 4th fewest September named storm days since 1950 (only 1962, 1970, and 1994 had fewer). The Accumulated Cyclone Energy (ACE) index for September ranked as the 6th lowest since 1950. The quiet period is likely to continue for at least another week, as there are no threat areas in the Atlantic to discuss today, and none of the computer models are forecasting tropical storm formation over the next seven days. I'll post my first-half-of-October outlook for the Atlantic tomorrow.

Jeff Masters

Hurricane

Typhoon Ketsana hits Vietnam; death toll in Philippines swells to 246

By: JeffMasters, 1:37 PM GMT on September 29, 2009

Typhoon Ketsana slammed into Vietnam this morning as a Category 2 typhoon with 105 mph winds. Ketsana brought sustained winds of 55 mph, gusting to 71 mph to Da Nang Vietnam. Heavy rainfall amounts of 7.2" and 9.1" were observed at Da Nang, and Hue, respectively, over the past two days. Floods and landslides in Vietnam from Ketsana's heavy rains have already claimed at least 22 lives.


Figure 1. Cars being swept away by Ketsana's flood waters in Manila's Park 9 Alley, where the Barangay Hall of Loyola Heights is located. Image credit: Manuel Quezon III.

The death toll in the Philippines from Ketsana continues to rise, with 284 dead or missing. The storm flooded the homes of 1.9 million people, leaving 350,000 people homeless. Ketsana brought 16.7 inches of rain in a twelve-hour period to Manila on Saturday, which was the heaviest 1-day rainfall ever recorded in the city. Ketsana is the third deadliest deadliest tropical cyclone to affect the globe so far this year. The deadliest was Typhoon Morakot, which left 654 people dead or missing on Taiwan, when it hit the island as a Category 2 typhoon on August 7. The second deadliest was Cyclone Aila, which made landfall near the India/Bangladesh border on May 25 as a tropical storm with 70 mph winds. Aila killed at least 339 people, 149 in India and 190 in Bangladesh.

The Philippines have three more tropical cyclones to their east to keep an eye on. So far, none of these storms appear to pose a major threat. Tropical Storm Parma is expected to curve to the northwest and miss the islands, Tropical Depression 18 is expected to dissipate, and newly-formed Tropical Depression 20 will probably pass to the north of the islands.


Figure 2. Rainfall from Tropical Storm Ketsana as estimated by NASA's TRMM satellite. Image credit: NASA Earth Observatory.

How to help Ketsana victims
Help the UN World Food Programme by making a donation. This program identifies families in specific need of aid. Just $18 provides a family with rice for two weeks. This is the most critical and immediate way you can make an impact.

Donate to the International Red Cross and help them continue to put relief workers on the ground in the Philippines.

Donate via Catholic Relief Services online of the Philippines or call 1-877-HELP-CRS.

Quiet in the Atlantic
None of the computer models are forecasting tropical storm formation in the Atlantic over the next seven days. Wind shear is predicted to be high in the Gulf of Mexico and Caribbean this week, limiting the potential for anything to affect land.

Jeff Masters

Hurricane

Philippines death toll from Ketsana rises to 140; Vietnam the typhoon's next target

By: JeffMasters, 12:52 PM GMT on September 28, 2009

The Philippine Islands continue to count the dead in the wake of the catastrophe left by Tropical Storm Ketsana on Saturday. Hard-hit was the capital of Manila, where the 16.7 inches of rain that fell in just 12 hours set a record for the heaviest 1-day rainfall ever recorded in the city (previous record: 13.2 inches in 24 hours, set in June 1967). In the six hours between 8am and 2pm local time on the 25th, Manila recorded 13.4 inches of rain--over 2.2 inches per hour. There rainfall rates were observable via satellite observations from NASA's TRMM satellite, well in advance of when the storm made landfall in the Philippines (Figure 2). The TRMM satellite showed a small core of heavy rain in excess of 1.6 inches per hours near the center of Ketsana, and this core moved directly over the city of Manila.


Figure 1. Cars being swept away by Ketsana's flood waters in a still frame from a dramatic YouTube video captured by medical students at the East Ramon Magsaysay Memorial Medical Center.

The flooding from Ketsana's rains was the worst in at least 42 years in Manila, and President Gloria Arroyo called Ketsana "a once-in-a-lifetime typhoon". At least 140 people are dead, 32 missing, and up to 450,000 homeless from the flooding in the Philippines.

Ketsana is not finished yet. The typhoon has begun a period of rapid intensification, and is now on the verge of attaining Category 2 typhoon status as it approaches a Tuesday landfall in Vietnam. Ketsana's heavy rains and high winds could exact a high toll in Vietnam.


Figure 2. Rainfall from Tropical Storm Ketsana as estimated by NASA's TRMM satellite, a few hours before the heavy rainfall began in Manila. Note the small core of heavy rain with rainfall rates off-scale (greater than 1.6 inches/hour) to the east of Manila. This region of heavy rain passed directly over the city between 8am and 2pm local time on 9/25/09. Image credit: Navy Research Lab, Monterey..

Quiet in the Atlantic
None of the computer models are forecasting tropical storm formation in the Atlantic over the next seven days. Wind shear is predicted to be high in the Gulf of Mexico and Caribbean this week, limiting the potential for anything to develop close to land.

Jeff Masters

Hurricane

Records rains in Philippines from Tropical Storm Ketsana kill at least 106

By: JeffMasters, 3:52 PM GMT on September 27, 2009

Tropical Storm Ketsana dumped prodigious amounts of rain on the Philippine Islands Saturday, triggering flooding that killed at least 106 people and left 280,000 people homeless. The flooding was particularly bad in the capital of Manilla, where the 16.7 inches of rain that fell in just 12 hours set a record for the heaviest 1-day rainfall ever recorded in the city (previous record: 13.2 inches in 24 hours, set in June 1967). The flooding from Ketsana was the worst in at least 42 years in Manilla, and the streets of the entire city became submerged in knee to waist deep or higher flood waters. Local news video showed dramatic footage of flood victims being swept down a suburban river on a pile of debris. Ketsana is currently over the South China Sea, and is expected to intensify into a Category 1 typhoon before hitting Vietnam on Tuesday.


Figure 1. Rainfall from Tropical Storm Ketsana as estimated by NASA's TRMM satellite.

In the Atlantic, Tropical Depression Eight dissipated yesterday, and there are no threat areas to discuss today. The GFS model is forecasting development of a tropical depression off the coast of Africa in about seven days time.

Jeff Masters

Hurricane

Tropical Depression Eight no threat to land

By: JeffMasters, 12:24 PM GMT on September 26, 2009

Tropical Depression Eight formed last night near the coast of Africa, but is not destined to threaten land, and has only about a 50/50 chance of becoming Tropical Storm Grace. While wind shear is a moderate 10 - 20 knots, Sea Surface Temperatures (SSTs) are right at the threshold for tropical storm formation--26°C. There is only a small amount of dry air that is interfering with the storm, but the combination of cool SSTs and moderate wind shear will make TD 8 slow to organize. By Monday, shear is expected to reach a very high 25 - 30 knots, and this should tear the storm apart.

None of the computer models are forecasting tropical storm formation elsewhere in the Atlantic over the next seven days.


Figure 1. Current satellite image of Tropical Depression Eight.

Jeff Masters

Hurricane

New tropical depression could form off the coast of Africa

By: JeffMasters, 1:12 PM GMT on September 25, 2009

A tropical wave (99L) is located near 15N, 30W, about 300 miles west of the Cape Verdes Islands. This wave has seen an increase in heavy thunderstorm activity this morning, and low-level spiral bands have formed. The system can already be classified as a tropical depression using the satellite-based Dvorak technique. This morning's QuickSCAT pass showed a loose but closed circulation, with top winds of 30 mph in the heaviest thunderstorms. Wind shear is moderate, about 10 - 20 knots. There is a modest amount of dry air to 99L's west that does not appear to be interfering with the storm's organization.


Figure 1. Morning visible satellite image of Invest 99L (left side of image) and a new tropical wave moving off the coast of Africa.

As 99L moves west-northwest over the next two days, sea surface temperatures will cool by 1°C and winds shear will remain in the moderate range. Some dry air may also affect the storm. These conditions give 99L a good chance of forming into a tropical depression, and NHC has given the system a moderate (30 - 50%) chance of developing into a tropical depression by Sunday. By Monday, wind shear will increase to the high range, 20 - 30 knots, and 99L will probably weaken or be torn apart. None of the computer models forecast development of 99L or any other system in the Atlantic over the next seven days.

A new tropical wave with plenty of heavy thunderstorm activity and some spin is moving off the coast of Africa today. This wave is under a moderate amount of wind shear, 10 - 20 knots, and has some potential for development this week as it moves west or west-northwest past the Cape Verdes Islands.

The latest wind shear forecasts from our major computer models show high values of wind shear affecting most of the tropical Atlantic for the next ten days. This is typical for an El Niño year, and it will be difficult for any storms to get to hurricane strength over the next ten days because of the high shear. The latest 16-day GFS forecast predicts wind shear will decline some by the 2nd week of October, though.


Figure 2. Wind shear forecast for Thursday, October 2 at 00 UTC made by last night's 00Z run of the GFS model. Wind shear is expected to be high over most of the tropical Atlantic for the next ten days, including the Caribbean. Wind shear values below 8 m/s (about 15 knots, red colors), are typically needed to support tropical storm formation.

Jeff Masters

Hurricane

The Age of Stupid--a movie review

By: JeffMasters, 1:45 PM GMT on September 24, 2009

I attended an interesting film premier Tuesday night--the international release of the anti-global warming pseudo-documentary The Age of Stupid. The movie opened at 440 theaters in the U.S., plus hundreds of theaters in 63 other countries, for a total viewing audience organizers estimated at one million people. This was a Guinness World Record for largest simultaneous movie premiere, according to the organizers. The evening began with a live satellite simulcast beamed from New York City, hosted by Gideon Yago of MTV/CNN fame. We were treated to live interviews with British director Franny Armstrong, producer Lizzie Gillett, as well as movies stars like Gillian Anderson (X-files) and Heather Graham ("we need to stop climate change, or else we're screwed"). Some humorous moments were provided by several protesters pretending to be corporate CEOs, who wore Model X7 Survivaballs as they rolled down the recycled pop-bottle green carpet (survivaballs' motto: "while others look to Senate bills or U.N. accords for a climate solution, we look to our best engineers"). We also heard rock star Moby perform on a sound stage powered by four bicyclists peddling on an specially-designed stationary bike rack. Very cute.

After about twenty minutes of these preliminaries, the 92-minute long Age of Stupid movie began. It opens with some beautiful computer animation of the Big Bang and four billion years of evolution, terminating in the year 2055. As the animation screeches to a halt, we are shown jarring scenes of London drowned by rising seas, Las Vegas drifted over by sand dunes, Sydney burning (eerily appropriate after yesterday's fiery red-orange skies spawned by Sydney's record dust storm), and a ruined Taj Mahal in a scorched landscape. I thought this was a bit overdone, since it is highly unlikely that climate change will be able to cause any of these effects by 2055. The scene then shifts to a futuristic building in the ice-free Arctic, where actor Pete Postlethwaite stars as the curator of an archive of human knowledge. He begins looking at old documentary footage from 2008 and asks the question, why didn't we stop climate change when we had the chance?


Figure 1. A flooded London in the year 2055 in The Age of Stupid.

The rest of the movie is a documentary, shot over the past four years in the UK, Nigeria, New Orleans, Iraq, Jordan, The Alps, and India. Six separate stories are followed:

Alvin DuVernay, a Shell Oil scientist who rescued 100 people after Hurricane Katrina
Layefa Malemi, a woman living in Shell's most profitable oil region in Nigeria
Jamila and Adnan Bayyoud, two Iraqi refugee kids trying to find their brother
Piers Guy, a wind farm developer fighting the anti-windfarm lobby in England
Fernand Pareau, 82-year old French mountain guide
Jeh Wadia, a businessman starting a low-cost airline in India

The six stories are interwoven and told in multiple sections, with jumps back and forth to curator Pete Postlethwaite in the future, who is viewing these documentary clips on his futuristic video screen. I found this creative approach to story telling a bit disorienting, but give the film maker credit for trying something innovative. Interspersed with the documentary footage are some fairly compelling animations. My favorite was an illustration of how America's excessive consumption is responsible for at least 1/4 of China's greenhouse gas emissions, since we buy so much cheap junk from China (which often ends up back in a China landfill). A lot of preaching goes on in the movie, with the film maker criticizing our excessive consumerism and our willingness to fight wars over oil. I thought the most compelling story of the six documentary pieces was the tale of the Nigerian woman living in the toxic mess that the oil industry has made in Nigeria. Cheap oil at the pumps in America has huge hidden costs that we don't appreciate.

While the movie did have some interesting sections with messages Americans need to hear, I thought overall the movie was too long and too dull to be worth spending a full-price movie admission ticket for. At least one of the six documentary sections should have been cut--92 minutes is too long for a documentary. It's pretty hard to make a gripping documentary movie about global warming, and The Age of Stupid and Al Gore's An Inconvenient Truth are not gripping. You're better off viewing these at home on DVD. Rating: two stars (out of four).

After the movie, the live simulcast from New York City resumed, and we heard speeches from Kofi Annan, former U.N. Secretary General, who called climate change "Perhaps the biggest challenge we face today". Also speaking was the President of the Maldives, an island nation mostly situated less than two meters above sea level. Sea level rise from climate change is a huge threat to his nation, and the president made a pledge to make his nation the first country to be carbon-neutral, by 2020. We also heard from the scientist who heads the U.N. Intergovernmental Panel on Climate Change, Rajendra K. Pachauri, who affirmed the movie's contention that we need to have global emissions of CO2 stop increasing by 2015 in order to avoid dangerous climate change.

The Age of Stupid as part of a media blitz
The release of The Age of Stupid this week was timed to bring visibility to the climate change issue and help mobilize public opinion in advance of the crucial U.N. Climate Change Conference, which will be held December 7 - 18 in Copenhagen, Denmark. At that meeting, the leaders of the world will gather to negotiate an agreement to replace the 1997 Kyoto Protocol. The new agreement will be the world's roadmap for dealing with climate change, and the stakes are huge. The Age of Stupid is key part of a major push green lobby push this week to publicize their key goals:

1) Reducing the 3% per year increase in CO2 emissions we've seen this decade to 0% by 2015.
2) An 80% reduction in CO2 emissions by 2050.
3) An eventual return to CO2 levels of 350 ppm--well below the current level of 388 ppm.

Activists are targeting the G-20 meeting in Pittsburgh this week as part of their effort; four Greenpeace protesters hung a "Danger: Climate Destruction Ahead, Reduce CO2 Emission Now" banner from a Pittsburgh bridge and dangled beneath the bridge for two hours yesterday. Greenpeace activists were also present as I walked out of the Age of Stupid premiere Tuesday, gathering signatures in support of a petition to urge CO2 controls be agreed upon at the December Copenhagen conference.

A return salvo from the fossil fuel industry and its allies is coming in the next few weeks. They have their own British film maker, Ann McElhinney, who has created a documentary titled, Not Evil Just Wrong, which premiers October 18. They've stated their goal of beating the record for simultaneous theaters airing a movie premiere set by The Age of Stupid. I'll be sure to write a review on Not Evil Just Wrong when it comes out.

Tropical update
There is a new tropical wave that moved off the coast of Africa yesterday that is generating some disorganized thunderstorm activity over the Cape Verdes Islands. This morning's QuikSCAT pass showed an elongated circulation two hundred miles southwest of the Cape Verdes Islands. Wind shear is a moderate 10 - 20 knots over the disturbance, and some slow development is possible over the next few days. The disturbance will have to overcome some dry air to its west, though. None of our reliable computer models are forecasting tropical storm development over the next seven days.

Jeff Masters

Climate Change

Massive duststorm chokes eastern Australia; Atlanta floods ease

By: JeffMasters, 2:22 PM GMT on September 23, 2009

A massive dust storm swept through eastern Australia today, turning the skies in Sydney a eerie shade of red-orange. The dust storm was reportedly the worst since the 1940s, and Sydney recorded its highest levels of particulate air pollution ever. The dust storm resulted from strong winds associated with a powerful low pressure system that swept through eastern Australia this morning. Winds today at the Sydney airport were sustained at 36 mph, gusting to 51 mph. Wind gusts as high as 64 mph were recorded in the Sydney area as the storm's strong cold front passed through. Particulate pollution levels are still in the hazardous range this evening in Sydney, but are expected to improve to the "good" range on Thursday as the winds die down and the dust storm dissipates.


Figure 1.. Strong northwesterly winds carry dust over Sydney, Australia, at 00 UTC 9/23/2009. Image credit: NASA.


Figure 2.. A strong cold front passing through eastern Australia this morning generated a sustained winds in excess of 20 mph over a large portion of the region.

Severe drought has affected large regions of Southeast Australia over the past three years (Figure 3). In isolated areas near Melbourne, the drought is the worst on record. The resulting loss of vegetation has created large regions of loose dust, which the strong winds from this week's storm was able to loft in the air and transport long distances.


Figure 3.. Rainfall deficiencies for Australia for the past three years. Image credit: Australian Bureau of Meteorology.

Atlanta floods ease
Very heavy rains exceeding fifteen inches soaked the Atlanta, Georgia region early this week, triggering widespread major flooding that continues today. Rainfall eased yesterday, and all of the rivers in the Atlanta area have crested and are now falling. Record flood levels were observed on at least seven rivers and creeks in the Atlanta area yesterday, breaking records that had been set as long ago as 1919. Utoy Creek near Atlanta broke its previous flood record by nearly 11 feet on Tuesday. The floods have killed at least nine people and did $250 million in damage. Portlight.org is experimenting with a new disaster relief strategy for this flood--they have decided to adopt a single family to help, the Baxter family of Lithia Springs, Georgia. The Baxters lost their home, car, furniture, clothes, and everything else in their house, and need assistance to defray the short-term expenses of lodging, food, and clothing, so help out if you can.


Figure 4. Radar estimated rainfall for the Atlanta, Georgia region ending on September 22. More than 15 inches (white colors) had fallen in and around Atlanta.

There are no threat areas in the Atlantic to discuss today, and none of our reliable computer models are forecasting tropical storm development over the next seven days.

Jeff Masters

Drought

Heavy rains kill seven in Georgia

By: JeffMasters, 1:27 PM GMT on September 22, 2009

Very heavy rains exceeding fifteen inches have soaked the Atlanta, Georgia region over the past two days, triggering widespread major flooding. Record flood levels have been observed on seven rivers and creeks in the Atlanta area, breaking records that had been set as long ago as 1919. In one case, the new flood record (for Utoy Creek near Atlanta), was more that ten feet above the previous record, with the creek still rising. The Chattahoochee River was one of the rivers that rose to record levels, and flood waters from the Chattahoochee crested over the I-285 bridge in western Atlanta, forcing closure of the expressway. At least seven people have been killed, according to ajc.com, with at least six people still missing.


Figure 1. Radar estimated rainfall for the Atlanta, Georgia region ending on September 22. More than 15 inches (white colors) had fallen in and around Atlanta.

A list of the records set so far:

Noonday Creek near Woodstock 19.66 ft 21/530 PM, old record 16.30 ft (07/11/2005)

Nickajack Creek at Mableton 19.30 ft 22/215 am, old record 16.60 ft (07/11/2005)

North Fork Peachtree Creek at Atlanta 18.07 ft 21/715 PM, old record 17.70 ft (09/16/2004)

Utoy Creek near Atlanta 27.04 ft 22/715 am, old record 16.86 ft (05/06/2003)...still rising

Chattahoochee River at Whitesburg 29.58 ft 21/1015 PM, old record 29.11 ft (12/11/1919)

Suwanee Creek at Suwanee 14.30 ft 21/645 PM, old record 12.04 ft (10/05/1996)

Yellow River at Lithonia 25.50 ft 22/515 am, old record 17.53 ft (05/07/2003)... nearly steady

Yellow River near Conyers 20.80 ft 22/730 am, old record 16.36 ft (07/08/2005) below Milstead...still rising

Chattahoochee River at Franklin 28.71 ft 22/715 am, old record 28.40 ft (12/15/1919)...still rising

The strong flow of moist air from the southeast that fueled the heavy rains has diminished today, and no widespread heavy rains will affect northern Georgia over the next few days. However, there will be some scattered thunderstorms in the region the next two days that will dump heavy downpours over local areas, and these thunderstorms will keep flood waters from receding much along some flooded rivers and creeks. It is possible that some additional moisture from the remains of Hurricane Fred will affect northern Georgia and South Carolina Wednesday and Thursday, boosting rainfall totals from these scattered thunderstorms.


Figure 2. AVHRR visible satellite image of Hurricane Hugo taken on September 22, 1989. Hugo was over Ohio at this time, and had finally been declared extratropical.

Twenty years ago today
Hurricane Hugo plowed through the center of South Carolina on September 22, 1989, reaching the North Carolina border 140 miles inland by 8am EDT. Amazingly, Hugo remained at hurricane strength for its entire passage through South Carolina--a full eight hours. The hurricane caused massive damage to forests, buildings, and power lines along the way, killing thirteen South Carolinans in total. Charlotte, North Carolina, over 200 miles inland, and a place of refuge for many South Carolinans that fled the storm, received sustained winds of 69 mph from Hugo--just below the 74-mph threshold of hurricane strength. Hugo turned northwards and roared through Virginia, where it killed six people, then into West Virginia and Ohio, where it was finally declared extratropical at 2pm EDT on the 22nd. The hurricane claimed its final victim near Buffalo, New York, when winds from Hugo toppled a tree onto a motorist.

In all, Hugo did $7 billion in damage to the continental U.S., and $10 billion over its entire path ($17.6 billion in 2009 dollars), making it the most costly hurricane ever at that time. The final death toll was 56.


Figure 3. Maximum wind gusts recorded from Hurricane Hugo of 1989. Wind gusts in excess of 80 mph (green hatched areas) were recorded all the way to the North Carolina border, 140 miles inland. Image credit: National Hurricane Center.

There are no threat areas in the Atlantic to discuss today, and none of our reliable computer models are forecasting tropical storm development over the next seven days.

Jeff Masters

Flood

Quiet in the Atlantic; lessons learned from Hurricane Hugo's storm surge

By: JeffMasters, 12:35 PM GMT on September 21, 2009

The tropical disturbance (98L), midway between Africa and the Lesser Antilles Islands, has grown weak and disorganized. No development of this disturbance is likely to occur.

The remains of Hurricane Fred are still kicking up heavy thunderstorms about 400 miles east of the Georgia-Florida border. Fred-ex's circulation has become ill-defined, as seen in last night's QuikSCAT pass. Fred-ex is under about 20 knots of wind shear, and this shear is expected to remain about the same over the next two days. Fred-ex will be moving ashore Tuesday night or Wednesday along a stretch of coast from Florida to North Carolina, bringing heavy rains to some areas. There is too much wind shear and dry air, and not enough time, for Fred-ex to develop into a tropical depression. I don't expect it to cause any flooding problems when it moves ashore.


Figure 1. Morning visible satellite image of Fred-ex, 400 miles east of Florida.

Twenty years ago today
On September 21, 1989, Hurricane Hugo began the day as a minimum-strength Category 3 hurricane with 115 mph winds. But as a strong trough of low pressure turned the hurricane to the north and accelerated Hugo to a forward speed of 25 mph, the storm took advantage of low wind shear and warm ocean waters to begin a period of rapid intensification. As darkness fell on the 21st, Hugo had grown to huge Category 4 hurricane with 135 mph winds. Its target: the South Carolina coast near Charleston, at Sullivan's Island. At 11:57 pm on the 21st, Hugo made landfall on Sullivan's Island. It was the strongest hurricane on record to hit South Carolina, and the second strongest hurricane (since reliable records began in 1851) to hit the U.S. East Coast north of Florida. Only Hurricane Hazel of 1954 (Category 4, 140 mph winds) was stronger.


Figure 2. AVHRR visible satellite image of Hurricane Hugo taken on September 21, 1989. Hugo had intensified to a formidable Category 4 hurricane with 135 mph winds.

On Isle of Palms, a barrier island adjacent to Sullivan's Island, the mayor and several police officers were sheltering in a 2-story building which lay at an elevation of ten feet. As related in a story published in the St. Petersburg Times, they heard the following bulletin on the radio at 10:30pm the night Hugo made landfall:

"The National Weather Service has issued a storm surge update. It appears that the storm surge will be greater than anticipated. It is now expected to reach a height of 17 to 21 feet."

"Mom didn't raise an idiot," said the one cop with the most sense, and he convinced the others to get off the island. They left the island by driving at 5 mph through horizontal sheets of rain and hurricane-force wind gusts over the Ben Sawyer Bridge, which connected Sullivan's Island to the mainland. As they crossed onto the bridge, they passed over a large bump--the bridge and road bed were at different levels. Not good. While crossing the bridge, they could feel it swaying and straining, and heard the sound of metal, twisting and grinding and breaking. They made it, but only barely--minutes later, the hurricane tore the center span of the bridge from its connection on both ends, leaving it a twisted ruin in the bay.


Figure 3. The Ben Sawyer Bridge connecting Sullivan's Island to Charleston, South Carolina, after Hurricane Hugo. Image credit: NOAA Photo Library.

Hugo's storm surge
In McClellanville, on the coast thirty miles northeast of Charleston, between 500 - 1100 people took refuge at the designated shelter for the region, Lincoln High School. Lincoln High is a one-story school, mostly constructed of cinder block, located on the east side of Highway 17, and was believed to be at an altitude of twenty feet. McClellanville is about 4 - 5 miles inland from the open ocean, but lies on the Intracoastal Waterway, so is vulnerable to high storm surges. Near midnight on the 21st, a storm surge of twenty feet poured into Bulls Bay just south of McClellanville, and funneled into the narrow Intracoastal Waterway. Water started pouring into the high school and rose fairly rapidly. Within minutes, people were wading around up to their waists, the water still rising. In the school cafeteria, many refugees gathered on a stage at one end, putting children up on tables. The elevated stage kept them above water; others floated in the water. Another group was in the band room, which had a much lower ceiling than the cafeteria. They had to stand on desks and push out the ceiling tiles for more breathing room, as the water rose within 1 - 2 feet of the ceiling. Fortunately, Hugo's storm surge peaked at that time, at about 16 - 17 feet (Figure 4), and the people sheltering at Lincoln High were spared.


Figure 4. Estimated storm surge (height above ground) as estimated by NOAA's storm surge model, SLOSH. McClellanville (upper right) received a storm surge estimated at 16 - 17 feet.

According to Dr. Stephen Baig, the retired head of the NHC storm surge unit, the back-story is this: To build Lincoln High School, which lies at an altitude of ten feet, the local school board used the same plans that were drawn up for another school that is west of Highway 17, and that IS at 20 feet elevation. Not only the same plans, the same set of working drawings. Those working drawings showed a surveyed elevation of 20 feet above datum (probably NGVD29). Apparently Lincoln High was constructed either without benefit of elevation survey or the plans were not annotated with its site elevation. When the Red Cross inquired as to its utility as an evacuation site, whoever looked at the plans saw the surveyed elevation at 20 feet. That is what the Red Cross published. That is why the school was a designated shelter. Since that near-tragedy, the Red Cross requires a new elevation survey for every potential storm shelter. I think that at the time this was discovered all the designated shelters also were re-surveyed, just to be sure that no similar Lincoln High problems were waiting to happen.

Only one person died from Hugo's storm surge, a woman who sheltered in her mobile home that got struck by the surge. Her death was one of only ten deaths that have occurred due to storm surge in the U.S. in the 35 years between 1969 - 2005 (after the 100+ storm surge deaths due to Hurricane Camille of 1969, and before the 1000+ storm surge deaths due to Hurricane Katrina). This amazingly low death toll can be attributed to four factors:

1) Greater understanding of the storm surge and better storm surge forecasts issued by the National Hurricane Center, thanks to such tools as the SLOSH storm surge model.
2) The excellent job NWS/NHC/FEMA and state and local Emergency Managers have done educating the public on the potential surge they can expect.
3) The success local government has had making evacuations of low-lying areas work.
4) Luck. The 20+ storm surge deaths on the Bolivar Peninsula in 2008 from Hurricane Ike show that there are still plenty of stubborn, unlucky, or uneducated people who will die when a significant storm surge hits a low-lying populated coast. The storm surge from the next major hurricane that sweeps through the Florida Keys is likely to cause a lot of storm surge deaths, since many residents there are pretty stubborn about not evacuating.

Kudos and links
I thank Ken Bass for providing the details on the Lincoln High storm surge near-disaster. Ken is working on a book on Hurricane Hugo, and has written a very readable book I plan to review later this year, about a fictional Category 4 hurricane hitting New York City.

Hurricanes-blizzards-noreasters.com has a web page with links to tons of Hurricane Hugo stories. Included are links to YouTube videos of a "Rescue 911" episode that interviewed survivors of the Lincoln High storm surge scare. The show also did a re-creation of the event.

Our Historical storm surge page has SLOSH model storm surge animations of Hurricane Hugo's landafall, as well as of 39 other famous hurricanes.

Tomorrow: I'll wrap up my series on Hurricane Hugo.

Jeff Masters

Hurricane

98L and Fred-ex pose little threat

By: JeffMasters, 3:21 PM GMT on September 20, 2009

A tropical disturbance (98L), is located midway between Africa and the Lesser Antilles Islands. This disturbance has lost most of its heavy thunderstorm activity over the past day. Last night's QuikSCAT pass showed an elongated circulation, with top winds around 30 mph. Wind shear is moderate, 10 - 15 knots, and Sea Surface Temperatures are 28°C, which is about 2°C above the 26°C threshold needed to support a tropical cyclone. There is a large amount of dry air to the north and west of 98L, and this dry air has been instrumental in disrupting development of 98L over the weekend.

Wind shear over 98L is expected to remain in the moderate range, 10 - 15 knots, through Tuesday evening, according to the SHIPS model. This may allow the storm to organize into a tropical depression, assuming it can fight off the dry air that surrounds it. Tuesday through Thursday, the SHIPS model predicts shear will increase to the high range, 20 - 25 knots, so it is unlikely 98L will become anything stronger than a weak tropical storm over the coming 5-day period. The models predict that a strong trough of low pressure will turn 98L to the northwest and then north beginning on Monday, with the result that 98L misses the Lesser Antilles Islands by at least 500 miles. NHC is giving 98L a medium (30 - 50%) chance of developing into a tropical depression by Tuesday. It does not appear that 98L will ever threaten any land areas. The GFDL and NOGAPS models develop 98L into a tropical storm; the other models do not.


Figure 1. Morning visible satellite image of Fred-ex (located at the tail end of a cold front draped over the Atlantic), and 98L.

Fred-ex
The remains of Hurricane Fred are still spinning away about 600 miles east of the Georgia-Florida border. Fred-ex's circulation has become ill-defined over the past day, and there has been no increase in heavy thunderstorm activity. High wind shear of 20 - 30 knots is affecting the storm, and there is also quite a bit of dry air interfering with development. The high wind shear and dry air will continue to affect Fred-ex over the next three days, as the storm moves west-northwest at 10 mph. Most of the models show the moisture from Fred-ex moving ashore between northern Florida and North Carolina Tuesday or Wednesday. None of the models develop Fred-ex, and I'm not expecting it to cause any flooding problems when it moves ashore.

Twenty years ago today
On September 20, 1989, Hurricane Hugo continued its steady northwest march at 15 mph towards the Southeast U.S., brushing the Bahama Islands along the way. Wind shear diminished, allowing the hurricane to intensify back to a major Category 3 hurricane with 115 mph winds. Hurricane watches and warnings had not yet been posted for the U.S. coast, but at noon on September 20, Mayor Riley of Charleston went on the air, telling residents of the city that Hugo was a killer. There was a very good chance that Hugo would be South Carolina's worst disaster this century, he said, with a storm surge up to fifteen feet high. Now, while the weather was good and the storm still far away, was the time to board up and get out.


Figure 2. AVHRR visible satellite image of Hurricane Hugo taken on September 20, 1989. Wind shear had diminished, allowing Hugo to intensify to a Category 3 storm with 115 mph winds. Image credit: Google Earth rendition of the NOAA HURSAT data base.

South Carolinans paid attention. Within an hour, residents jammed hardware stores and supermarkets. Traffic on roads away from the coast swelled as people scrambled to flee the arrival of the first major hurricane to strike South Carolina in thirty years--since Category 3 Hurricane Gracie of 1959 slammed into the coast south of Charleston.

At 6 pm, it became official: the Southeast U.S. coast from St. Augustine to Cape Hatteras had been placed under a hurricane watch, meaning that hurricane conditions could be expected within 36 hours. The torrent of evacuees leaving the coast swelled, reaching a million people in all.

In the U.S. Virgin Islands, the aftermath of Hugo became desperate as widespread looting erupted on St. Croix, forcing President Bush to send 1,100 troops. Wunderground member Mike Steers was there, and relates this story: "Surviving the aftermath was the real challenge. The lack of power, water, communications of any kind, and the crime and looting was the real test. After about a week of digging out of the remains of the house and neighborhood I was able to venture out on my motorcycle to see what had become of my job. On the way, I personally witnessed the looting and lawlessness. I even saw a National Guard truck backed up to what was a appliance store and the guardsmen were helping themselves to washers and dryers. Never mind that there was no power to run them. When I got to the seaplane ramp, I saw the total destruction that is depicted in one of the photos I sent. On my way home, there was a small local grocery store I had usually gone to, and I was going to stop in and see how the owners were doing. There was a band of youths in the process of carrying out everything that was not nailed down. From the back, out ran a rastaman with a machete saying he wanted my motorcycle. Needless to say, I gunned it and got back to my house as soon as possible. My neighbors and I set up our own armed 24-hour security checkpoint to protect ourselves. It was about a week later that the first of the giant C-5s flew over, sent by President Bush to start to restore order..."


Figure 3. Newspaper headline from the Virgin Islands Daily News after Hurricane Hugo, detailing the looting problems on St. Croix. Image scanned in by Mike Steers.

Jeff Masters

Hurricane

Hurricane Hunters to check out remains of Fred; 98L more organized

By: JeffMasters, 1:06 PM GMT on September 19, 2009

A tropical disturbance (98L), is located midway between Africa and the Lesser Antilles Islands. This disturbance has shown a modest increase in heavy thunderstorm activity over the past day. This morning's QuikSCAT pass showed an elongated circulation, with top winds around 30 mph. Wind shear is low, 5 - 10 knots, and Sea Surface Temperatures are 28°C, which is about 2°C above the 26°C threshold needed to support a tropical cyclone. There is a large amount of dry air to the north and west of 98L, and this dry air is interfering with development.

Wind shear over 98L is expected to remain in the low range, 5 - 10 knots, through Sunday evening, according to the SHIPS model. This may allow the storm to organize into a tropical depression, assuming it can fight off the dry air that surrounds it. By Monday, the SHIPS model predicts shear will increase to the high range, 15 - 30 knots, so in is unlikely 98L will become anything stronger thatn a weak tropical storm over the coming 5-day period. The models predict that a strong trough of low pressure will turn 98L to the northwest and then north beginning on Monday, with the result that 98L misses the Lesser Antilles Islands by at least 500 miles. NHC is giving 98L a high (greater than 50%) chance of developing into a tropical depression by Monday. At this time, it does not appear that 98L will ever threaten any land areas.

Fred-ex
The remains of Hurricane Fred are still spinning away about 700 miles east of Florida. There has been a modest increase in heavy thunderstorm activity on the south side of Fred's circulation over the past day, but high wind shear and dry air have kept the thunderstorms from building over Fred's center. Wind shear is moderate, 15 - 20 knots, and there is substantial dry air surrounding ex-Fred on all sides. This morning's QuikSCAT pass showed top winds of 30 mph.

None of the computer models develop ex-Fred, and conditions for development are expected to remain marginal over the next three days, with wind shear of 15 - 20 knots and plenty of dry air around. Most of the models predict ex-Fred should move over Florida on Tuesday, but steering currents may weaken early next week, and ex-Fred could end up slowing down and turning northwest towards South Carolina. A hurricane hunter aircraft this afternoon was cancelled.


Figure 1. Morning visible satellite image of 98L and the remains of Hurricane Fred.

Twenty years ago today
On September 19, 1989, Hurricane Hugo moved away from Puerto Rico, and headed northwest at 15 mph. An upper-level low over Georgia, in combination with the steering currents imparted by the Azores-Bermuda High, were responsible for the northwesterly motion of the storm. Wind shear from strong upper-level winds continued to weaken the hurricane, and Hugo diminished to a Category 2 hurricane with 105 mph winds.


Figure 2. GOES visible satellite image of Hurricane Hugo taken on September 19, 1989. Wind shear had weakened Hugo to a Category 2 storm with 105 mph winds. Image credit: Google Earth rendition of the NOAA HURSAT data base.

I'll have an update this afternoon if there's any major developments to report.

Jeff Masters

Hurricane

Disturbance 98L probably no threat to land

By: JeffMasters, 1:46 PM GMT on September 18, 2009

A tropical disturbance (98L), is located midway between Africa and the Lesser Antilles Islands. This disturbance has a well-defined surface circulation, and has developed a modest amount of heavy thunderstorm activity overnight. This morning's QuikSCAT pass (Figure 1) shows a complete, circular wind pattern around the low pressure center of 98L, but top winds were only 25 mph. Wind shear is moderate, about 15 knots, and Sea Surface Temperatures are 28°C, which is about 2°C above the 26°C threshold needed to support a tropical cyclone. There is a large amount of dry air to the north and west of 98L, and this dry air is interfering with development.

The global computer models predict differing amounts of wind shear in the path of 98L as it moves west-northwest at 10 mph over the next three days. The ECMWF, GFS, and UKMET models do not develop 98L, while the NOGAPS, GFDL, and HWRF do. The models that do develop 98L predict that a strong trough of low pressure will turn 98L to the northwest and then north beginning on Monday, with the result that 98L misses the Lesser Antilles Islands by at least 500 miles. Given the moderate or higher wind shear in 98L's path, and dry air to the northwest, the system should develop only slowly. NHC is giving 98L a medium (30 - 50%) chance of developing into a tropical depression by Sunday. At this time, it does not appear that 98L will ever threaten any land areas.

The remains of Hurricane Fred are still spinning away, near 25N 66W, about 900 miles east of Florida. Wind shear is 20 knots, which is marginal for development, and there is very dry air surrounding ex-Fred on all sides. None of the computer models develop ex-Fred, and it will have a tough time regenerating with so much dry air and wind shear. The remains of Fred should move over Florida Monday night or Tuesday morning.


Figure 1. Morning QuickSCAT image of the Atlantic, showing the well-defined surface circulation of disturbance 98L. Image credit: NOAA/NESDIS.

One year anniversary of Hurricane Ike
I've been focusing this week on the 20th anniversary of Hurricane Hugo, but we also passed the one year anniversary of Hurricane Ike. Many areas along the Texas and Louisiana coast affected by Ike have fully recovered, but recovery efforts will still take many more years in other areas. In Galveston, which suffered $3.2 billion in damage, 75% of the businesses have reopened, and 95% of the population has returned. Boston.com has posted a very nice series of clickable images that show before and after scenes of some of the areas that have recovered from Hurricane Ike.

Ike washed away huge sections of beach and dunes that helped protect the Texas coast from more serious damage, and this week the state legislature approved $135 million in funds to help replace these critical natural protection systems. The restored beaches will probably last ten years, barring another strike by a hurricane of Ike's stature. Texas considers two-thirds of its 367-mile shoreline to be critically eroding, which it defines as a historical rate of more than 2 feet a year. Much of this erosion can be blamed on sea level rise. Global sea level rose seven inches over the past century, and is expected to rise at least that much over the coming century.


Figure 2. Villagers in Haiti plant one of their "Million Tree Campaign" trees. Image credit: Lambi Fund of Haiti.

Hurricane relief donations
There hasn't been a need for new hurricane-related disaster relief efforts this year, in stark contrast to 2008. However, the charities we rely on to provide disaster relief still require funds to operate in quiet years, and I encourage you to consider a donation at this time to one of my two favorite disaster relief charities. Portlight.org, which was very effective at helping out isolated, under-served communities in the wake of Hurricane Ike, is committed to raising $12,000 to purchase and outfit a mobile kitchen. This kitchen will be capable of feeding up to 2,000 people two hot meals per day in post-disaster situations. The Lambi Fund of Haiti has launched its "Million Tree Campaign", which aims to use local labor to plant a million trees over the next three years along severely deforested slopes in Haiti. Both of these charities wrote to me several times last year about the stunning generosity readers of this blog showed with their donations. Thanks!

Twenty years ago today
As Hurricane Hugo approached the U.S. Virgin Islands in the early morning hours of September 18, 1989, the storm slowed down to 10 mph. The slower speed allowed Hugo to punish the island of St. Croix with the worst beating of any location along the hurricane's destructive path. At 2am local time on September 18, 1989, Hurricane Hugo's eyewall struck St. Croix, bringing incredibly ferocious Category 4 winds, sustained at 140 mph. The hurricane's gusts were remarkably violent, and many residents witnessed tornado-like vorticies barreling across the island as the hurricane raged about them. A storm surge of 2 - 3 feet, topped by battering waves 20 - 23 feet high, assaulted the coast, adding to the destruction. Wunderground member Mike Steers wrote me to describe his experience on St. Croix: "Hugo was incredible. Many vortexes came in that night. The roar and intensity of the winds that night were incredible. When the eyewall came over, we were forced to take refuge in the bathroom as the rest of the house came apart. The pressure was so low outside the house that all of the water was sucked out of the toilet and an air draft was created through the toilet. Just when I thought it was as bad as it would get, the intensity of it all dialed up even higher. Dozens and dozens of times, my ears would violently pop due to rapid pressure changes. The next morning, of course, the devastation was unbelievable. In my front yard was a 18-foot boat with an outboard on it, that had been picked up from a marina two miles away. I had lost my house, and job, the Seaplane company I was a pilot for. After a couple months, I had to leave everything behind. In some respects, after 20 years, there an many aspects of the society that have yet to recover". Two people were killed on St. Croix, 80 injured, and 90% of the buildings were damaged or destroyed. Damage estimates for St. Croix were astronomical, over $1 billion, and the island's entire infrastructure was virtually wiped out. Six weeks after the hurricane, only 25% of the public roads had been cleared, and only 25% of the island had power.


Figure 3. GOES visible satellite image of Hurricane Hugo taken on September 18, 1989. Note the lack of cloud cover on the hurricane's southwest side, indicating that strong upper-level winds from the southwest were likely creating wind shear, weakening the storm. Image credit: Google Earth rendition of the NOAA HURSAT data base.

As Hugo departed St. Croix, strong upper-level winds from the southwest created wind shear that weakened the storm to a Category 3 hurricane with 130 mph winds. The upper level winds also caused Hugo to accelerate to 15 mph and turn more northwest. The eye passed over Puerto Rico's Vieques Island at 8am and over Fajardo on the extreme northeastern tip of Puerto Rico at 9am. On Culebra Island, an island twelve miles east of Fajardo, a gust to 170 mph was recorded by the ship Night Cap in the main harbor. The south-facing harbor received sustained southerly winds in excess of 120 mph for several hours as Hugo roared by to the south. The resulting wave "set-up" created a storm surge in excess of 13 feet in the supposedly hurricane-proof harbor. A large portion of the Caribbean's charter boat fleet, some 200 boats, was sheltering in Culebra's harbor, and 136 of these boats were badly damaged or sunk. Over 80% of the wooden structures on both Culebra and Vieques were destroyed.


Figure 4. Damage on St. Croix (two top photos), Culebra Island (bottom right), and Puerto Rico's Roosevelt Roads Navy Base (bottom left), after Hurricane Hugo. Image credit: NOAA Photo Library.

Along the northeastern coast of Puerto Rico, waves up to ten feet high riding on top of a 3 - 4 foot storm surge caused severe coastal flooding of low-lying areas. Hugo's winds tore into Puerto Rico's El Yunque rainforest, downing thousands of trees. The agricultural sector was devastated, with nearly all of the island's banana and coffee crops wiped out. Twelve deaths in Puerto Rico were attributed to Hugo, six of which occurred in the southern city of Guayama where some residents were electrocuted by downed power lines. Nearly 28,000 people were left homeless by the storm, and damage to the island exceeded $1 billion.

Storm chaser Michael Laca was at Luquillo Beach on the northeast shore of Puerto Rico, and has posted a remarkable 28-minute video on YouTube of Hurricane Hugo footage.

Jeff Masters

Hurricane

Global ocean temperatures at record highs for 3rd consecutive month

By: JeffMasters, 2:04 PM GMT on September 17, 2009

For the third consecutive month, global Sea Surface Temperatures (SSTs) were the warmest on record, according to statistics released yesterday by the National Climatic Data Center. August SSTs were 0.57°C (1.03°F) above the 20th century average, breaking the previous August record set in 1998. The record August SSTs were due in part to the continuation of El Niño conditions in the Eastern Pacific, which have substantially warmed a large stretch of the tropical Eastern Pacific Ocean. El Niño conditions are expected to amplify during the coming months, and record or near-record global ocean temperatures will probably continue.

August global surface temperatures 2nd to 6th warmest on record
The globe recorded its second warmest August since record keeping began in 1880, according to NOAA's National Climatic Data Center. NOAA rated the period June - August (summer in the Northern Hemisphere, winter in the Southern Hemisphere) as the third warmest on record, and the year-to-date period, January - August 2009, as the fifth warmest such period on record. NASA's Goddard Institute for Space Studies rated August 2009 as the 6th warmest August on record, and the period June-July-August as the 2nd warmest on record. The August satellite-measured temperatures for the lowest five miles of the atmosphere were between 7th and 9th warmest on record, according to the University of Alabama in Huntsville and Remote Sensing Systems.

Warmest August on record in Australia and New Zealand
Australia had its warmest August on record in 2009, according to the Australian Bureau of Meteorology. Temperatures averaged a remarkable 3.2°C (5.8°F) above average, making August 2009 the most anomalous month ever recorded in Australia. The previous record was set in April 2005, which was 3.1°C (5.6°C) above average. The month's highest temperature, 39.7°C (103°F) at Wyndham Airport on the 31st, fell only 0.3°C short of the Australian record for August. The Australian winter (June-July-August) was the 2nd warmest on record, next to the winter of 1996. New Zealand also experienced its warmest August on record (records go back 155 years).

A cool August and cool summer for the U.S.
For the contiguous U.S., the average August temperature was 0.6°F below average, making it the 30th coolest August in the 115-year record, according to the National Climatic Data Center. The U.S. as a whole was below normal for the summer period (June - August). A recurring upper level trough held the June - August temperatures down in the central states, where Michigan experienced its fifth coolest summer, Wisconsin, Minnesota, and South Dakota their seventh coolest each, Nebraska its eighth, and Iowa its ninth. In contrast, the temperatures in Florida averaged out to be fourth warmest, while Washington and Texas experienced their eighth and ninth warmest summers, respectively.

U.S. precipitation in August was below average, as the month ranked 28th driest in the 115-year record. Arizona had its fourth driest August, New Mexico its fifth, and it was the eighth driest August for Colorado, Utah and Texas. Arizona observed its third driest summer, while both South Carolina and Georgia had their sixth driest. It was the 8th wettest summer on record in the Northeast.

At the end of August, 13% of the contiguous United States was in moderate-to-exceptional drought. This is a drop from the 19% figure observed at the beginning of the year. These extreme drought regions were exclusively in South to Central Texas. However, significant drought relief occurred in this region the second week of September, when a large area of tropical moisture settled in over the region, bringing heavy rains. About 19 percent of the contiguous U.S. fell in the severely to extremely wet categories in August.

Weak El Niño conditions continue
El Niño conditions continue over the tropical Eastern Pacific. Ocean temperatures in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", were 0.4°C above the threshold for a weak El Niño, according to the Australian Bureau of Meteorology. NOAA's Climate Prediction Center is maintaining an El Niño Advisory. Current conditions and model forecasts favor the continued development of a weak-to-moderate strength El Niño into the Northern Hemisphere Fall 2009, with the likelihood of at least a moderate strength El Niño (3-month Niño-3.4 SST index of +1.0°C or greater) during the Northern Hemisphere Winter 2009-10.

Sea ice extent in the Arctic 3rd lowest on record
August 2009 Northern Hemisphere sea ice extent was the 3rd lowest since 1979, according to the National Snow and Ice Data Center, behind 2006 and 2007. Sea ice extent has increased slightly over the past week, and we have probably reached the minimum for the year. If so, this year's minimum ranks as the 3rd lowest, behind 2007 and 2008. The fabled Northwest Passage appeared to melt free for brief period in August, according to the National Snow and Ice Data Center. This marks the third consecutive year--and third time in recorded history--the Northwest Passage has opened. The Northeast Passage along the north coast of Russia also opened up this year. This is the fourth time in the past five years the Northeast Passage has opened, and the fourth time in recorded history.

Quiet in the Atlantic
The remains of Hurricane Fred are generating a very small amount of heavy thunderstorm activity near 23N, 61W. These thunderstorms were generating winds up to 35 mph, according to this morning's QuikSCAT pass. However, QuikSCAT also showed that the remains do not have a surface circulation, and the organization of ex-Fred has degraded to point where NHC is no longer mentioning the system on their Tropical Weather Outlook. Water vapor satellite loops show that ex-Fred continues to suffer from dry air thanks to an upper-level low pressure system, and it is unlikely that Fred will ever regenerate. None of the computer models call for any tropical cyclones to develop anywhere in the Atlantic over the next seven days.


Figure 1. Two views of the eye of Super Typhoon Choi-wan. Left: the eye at 01:25 UTC 9/16/09, when Choi-wan was a Category 5 storm with 160 mph winds. Right: the eye at 03:40 UTC 9/17/09, when Choi-was was a Category 4 storm with 150 mph winds. Image credit: MODIS Rapid Response System.

Typhoon Choi-Wan no longer a Category 5 storm
This year's first Category 5 tropical cycloneTyphoon Choi-Wan, has fallen to Category 4 strength after spending 42 hours as a 160 mph Category 5 storm. Choi-Wan--in Cantonese, a type of cloud--is over the open ocean south of Japan, and is not expected to impact any land areas. Choi-wan passed over tiny Alamagan Island, population 15, yesterday. All residents on the island were reported safe.

On this day twenty years ago
At 1 am AST on September 17, 1989, Hurricane Hugo made a direct hit Guadeloupe, pounding the island with Category 4 sustained winds of 140 mph. A storm surge of up to 2.5 meters (8 feet) topped by high battering waves smashed ashore. Hugo wreaked massive devastation on Guadeloupe, destroying 10,000 homes, leaving 35,000 of the island's 340,000 people homeless. Four people died and 107 were injured. An additional seven people were killed three days after the storm when a medical helicopter crashed while evacuating victims. Hugo's winds knocked the airport control tower out of commission, and almost completely destroyed the town of St. Francious, on the island's eastern end. Debris blocked at least 30% of the island's roads. Agriculture suffered massive losses that took years to recover from, as Hugo flattened 100% of the banana crop, 60% of the sugar cane crop, and ruined nearly all of the island's coconut palms. Most of the island's fishing fleet was wiped out, and total damage to the island from Hugo amounted to $880 million. Hugo was the strongest hurricane to hit the island since the legendary 1899 San Ciriaco Hurricane--the longest-lived Atlantic hurricane of all time--which brought 150 mph winds to Guadeloupe.


Figure 2. AVHRR visible satellite image of Hurricane Hugo taken on September 17, 1989. Image credit: Google Earth rendition of the NOAA HURSAT data base.

Hugo continued northwest and pulverized its next target, the island of Montserrat, several hours later. Though the eye missed Monserrat, the severe right front quadrant of Hugo's eyewall, still packing sustained winds of 140 mph, pounded the island. Nearly every home on Monserrat was destroyed or heavily damaged, leaving 11,000 of the island's 12,000 people homeless. Numerous schools, hospitals, and churches were destroyed, along with the police department, the government headquarters, and the main power station. Twenty foot waves in the harbor of the main town, Plymouth, destroyed the 180-foot stone jetty, and heavy rains of up to seven inches created mudslides that at the foot of Chances Peak that destroyed 21 homes. Ten people were killed on Montserrat, 89 injured, and damage topped $260 million, making it the most expensive hurricane in the island's history. Elecrtic, water, and telephone service were disrupted for weeks, necessitating a massive U.S. and British relief effort.


Figure 3. Hugo's storm surge inundates the coast of Montserrat Island. Image credit: NOAA photo library.

The nearby islands of St. Kitts, Antigua, St. Martin, Anguilla, and Dominica did not receive a blow from Hugo's eyewall, but damage was heavy nonetheless. One person was killed on Antigua, and 30% of the homes damaged. Dominica suffered the loss of 80% of its banana crop, and landslides cut off many towns for days. Shoreline erosion damage and crop losses totaled $43 million on St. Kitts, where one person was killed.

Jeff Masters

Climate Summaries

First Category 5 storm of the year is Choi-Wan

By: JeffMasters, 1:38 PM GMT on September 16, 2009

The remains of Hurricane Fred continue to generate sporadic bursts of heavy thunderstorm activity over the middle Atlantic Ocean. These thunderstorms were generating winds up to 30 mph, according to this morning's QuikSCAT pass. However, QuikSCAT also showed that the remains no longer have a surface circulation. Water vapor satellite loops show that ex-Fred has moved beneath an upper-level low pressure system. This low features dry air on all sides, and this dry air will interfere with any redevelopment of Fred. While wind shear is now moderate, 10 - 15 knots, and is expected to remain in the moderate range for the next five days, the presence of so much dry air will require at least three days for the remains of Fred to overcome and regenerate a surface circulation. Only the HWRF model redevelops Fred, predicting it will develop on Sunday as it approaches the Bahama Islands. NHC is giving ex-Fred a low (less than 30% chance) of developing into a tropical depression by Friday. Fred's remains will be near the Bahamas on Sunday, and near Florida on Monday night. It is possible that a strong trough of low pressure expected to develop over the eastern U.S. early next week will turn Fred's remains northwards into South Carolina/North Carolina on Monday/Tuesday.

This morning's QuikSCAT pass shows a surface circulation near 13N 32, with a small region of heavy thunderstorms to the north. This region is about 450 miles west of the Cape Verdes Islands, and is headed west at about 10 mph. Satellite imagery shows a decrease in the amount of heavy thunderstorm activity this morning, and high wind shear of 20 knots is interfering with development. A band of high wind shear lies just to the north of the disturbance, and will continue to interfere with the system's development over the next three days. NHC is giving the system a low (less than 30% chance) of developing into a tropical depression by Friday.

The GFS model is predicting development of a new tropical wave coming off the coast of Africa early next week.


Figure 1. The remains of Hurricane Fred (left) keep on chugging across the Atlantic. A tropical wave is 450 miles west of the Cape Verdes Islands (right). The thunderstorms of the Inter-Tropical Convergence Zone (ITCZ) are far to the south, off the coast of Africa.

Super Typhoon Choi-Wan hits Category 5 strength
This year's first Category 5 tropical cyclone is Super Typhoon Choi-Wan, which intensified into a Category 5 storm with 160 mph sustained winds yesterday afternoon. Choi-Wan is over the open ocean south of Japan, and is not expected to impact any land areas. It is unusual to have to the globe's first Category 5 storm form this late in the year. Indeed, global tropical cyclone activity as measured by the ACE index, which measures destructive potential, has been near historic lows over the past two years. Only one Category 5 storm was recorded in 2008--Super Typhoon Jangmi, which attained winds of 165 mph at 06 GMT on September 27, as it approached the north coast of Taiwan. The last time so few Category 5 storms were recorded globally was in 1974, when there were none.

We got a rare treat yesterday when the Cloudsat satellite caught a perfect cross section through Choi-Wan when it was a Category 4 super-typhoon with 150 mph winds (Figure 2). The CloudSat satellite, launched in 2006, carries the first satellite-based millimeter wavelength cloud radar. It is the world's most sensitive cloud-profiling radar, more than 1000 times more sensitive than current weather radars. It collects data about the vertical structure of clouds, including the quantities of liquid water and ice, and how clouds affect the amount of sunlight and terrestrial radiation that passes through the atmosphere. The satellite has a narrow field of view, so can image only a small portion of the planet each day. About once per year, CloudSat happens to slice through the eye of an Atlantic hurricane. This happened last month, when Cloudsat caught a remarkable view of Hurricane Bill.


Figure 2. Top: conventional visible satellite image of Super Typhoon Choi-Wan at 3:57 UTC Tuesday, 9/15/09 from Japan's MTSAT. Bottom: cross section through Choi-Wan's eye taken at the same time, from the CloudSat cloud radar instrument. The CloudSat pass occurs along the red line in the top image. The CloudSat pass runs from south (left side of CloudSat image) to north (right side of CloudSat image). At the time of the image, Choi-Wan was strengthening into a Category 4 Super Typhoon (150 mph winds, 928 mb pressure), and reached Category 5 strength fourteen hours after this image was taken. In the CloudSat image, one can see 6+ isolated towers, marking the positions of spiral bands on the south side of the center. The eye is remarkably well-defined, with symmetric "hot towers" extending up to 55,000 feet, sloping outward with height. The thin solid grey line at 5 km marks the 0°C temperature line. Ice particles falling inside the hurricane melt at an altitude just below the 0°C line, creating a "bright band" of orange echoes throughout most of the hurricane. This is one a few inner eye images CloudSat has captured of an Category 4/5 tropical cyclone. Image credit: NASA/Colorado State University/Navy Research Lab, Monterey.

Twenty years ago today
On September 16, 1989, Hurricane Hugo weakened slightly as it underwent an eyewall replacement cycle. The tight inner eyewall that we had flown through the previous day had contracted to the point where it became unstable and collapsed. A new eyewall formed out of an outer spiral band, and Hugo's highest winds dropped to 140 mph--Category 4 strength. As this was occurring, the storm began a more northwesterly path and slowed down, in response to a region of low pressure north of Puerto Rico. By midnight, Hugo was only an hour away from its first encounter with land--the Lesser Antilles island of Guadeloupe.

Back on Barbados, our one undamaged P-3 Orion Hurricane Hunter aircraft flew a mission into Hugo, while the crew of the damaged aircraft remained on the ground. Our plane was grounded until a team of experts from the mainland could fly out and perform a detailed x-ray analysis of the wings to determine if the high g-forces we endured had caused structural damage. This might take a week, so the plan was to fly us back to Miami on a commercial jet. However, Hugo had forced the cancellation of virtually every commercial flight in the eastern Caribbean that day, so we were stuck on the island. Most of us spent a frustrated day touring the island on rented mopeds, getting a look at Hugo from the ground. We got thoroughly drenched by one of Hugo's outermost spiral bands, but the hurricane was too far away to bring any winds more than 20 mph to the island.

That night, our already jangled nerves got a new jolt--a tropical depression had formed due east of Barbados, and was headed right for us. In two days time, it seemed likely that Tropical Storm Iris would be paying us a visit.


Figure 3. AVHRR visible satellite image of Hurricane Hugo taken on September 16, 1989. Image credit: Google Earth rendition of the NOAA HURSAT data base.

Jeff Masters

Hurricane

A flight through Hurricane Hugo, remembered 20 years later

By: JeffMasters, 1:21 PM GMT on September 15, 2009

The remains of Hurricane Fred continue to generate sporadic bursts of heavy thunderstorm activity over the middle Atlantic Ocean. These thunderstorms were generating winds up to 35 mph, according to this morning's QuikSCAT pass. Dry air and high wind shear of 20 - 25 knots today and Wednesday will continue to prevent regeneration of Fred. By Thursday, the chances for regeneration of Fred increase, since wind shear near Fred's remains will fall below 20 knots. However, continued high wind shear and dry air over the next two days will further disrupt the remains of Fred, and there may not be enough left of the storm to regenerate from by the time the wind shear drops. The NOGAPS model forecasts that Fred could regenerate by Sunday, when the remains of the storm will be approaching the Bahama Islands.

Satellite imagery shows a small circulation associated with a tropical wave about 200 miles west of the Cape Verdes Islands. Heavy thunderstorms activity has increased in this region over the past day. However, wind shear is near 20 knots, which is marginal for development, and shear will increase to near 30 knots as the wave progresses west-northwest into a band of high wind shear that lies to its north. It is unlikely that this wave can develop into a tropical depression this week, and NHC is giving it a low (less than 30% chance) of developing into a tropical depression by Thursday.

Tropical storm development is possible this week along a frontal zone stretching from the Bahamas northeastward. Anything that develops may end up being extratropical in nature, and would likely move northeastward out to sea.

The GFS model is predicting development of a new tropical wave coming off the coast of Africa early next week.


Figure 1. The remains of Hurricane Fred (left) appears as a swirl of low-level clouds with a clump of heavy thunderstorm activity on the northwest side. A tropical wave is 200 miles west of the Cape Verdes Islands (right), off the coast of Africa. This wave is probably under too much wind shear to develop.

A flight through Hurricane Hugo, remembered 20 years later
The events of September 15, 1989, have affected me more deeply than those of any other day in my life. The fifteen members of our crew very nearly became the first of Hurricane Hugo's many victims, and I am still grappling twenty years later with the emotional fallout from the experience. (If you are troubled by a traumatic experience, you may want to consider EMDR therapy, which I found to be helpful). The process of writing the story of that flight was also very therapeutic, and I worked intermittently for six years on the story while I was working towards my Ph.D. For those of you who haven't read it, do so! I worked very hard on it, and it is a remarkable story.


Figure 2. GOES visible satellite image of Hurricane Hugo taken on September 15, 1989. Image credit: Google Earth rendition of the NOAA HURSAT data base.

The Hurricane Hunters often carry reporters and camera crews on their flights, and the unlucky soul on our flight through Hurricane Hugo was young Janice Griffith of the Barbados Sun newspaper. Her account:

Horror of Hugo's Eye
TO a young reporter, with perhaps more journalistic curiosity than is good for her, it seemed a chance for a good story. To others, who were quick to tell me so, a flight into the centre of a powerful and dangerous hurricane was "sheer madness".

In the end, my journey Friday on a "Hurricane Hunter" aircraft with a hardened, professional crew was nerve-shattering, awesome, and unforgettable. When we limped back into Grantley Adams International after a beating from nature's fury in the form of Hurricane Hugo, I had my story. But I also had to agree that I must have been crazy to have gone in the first place.

Not that I wasn't forewarned.

You sure you want to go?" Dr. James McFadden, manager of the airborne science programmes of the United States Department of Commerce and head of the team asked when I raised the subject following their arrival from their Miami base on Thursday night. "It can be a very dangerous trip".

I wasn't fazed. After all, I'd flown a lot on commercial aircraft, from LIAT to large jumbo jets, and these hurricane hunter were experts who, I was assured, had been in the business of tracking storms in the Atlantic and Caribbean for a dozen years or more. Some had even been at it for 18.

They'd all been through and gone into the eyes of dozens of hurricanes and come back to tell the tale. Not even apprehensive as I, the only woman along with 10 men, boarded just before noon Friday and was shown to one of the four seats in the cockpit, just behind pilot Gerry McKim.

No hostess coming through with complimentary drinks here--or clicking on a seat belt. I was harnessed in like an infant in the rear seat of a car, waist and shoulders securely strapped. "Just in case", I was told.

While I observed, wide-eyed, everyone went about his business with the facility of someone who has done it all before a hundred times over--the pilot and co-pilot, Lowell Genzlinger, the flight engineer, the navigator, the weather experts. Everyone.

Calming effect
Their efficiency had a calming effect and the first half-hour or so, as we headed northeast to investigate and report on the details of Hugo's size and power, was no rougher than any commercial flight I've been on.

But then the sky began to close in with heavy, dark clouds and the 14-year old turboprop plane began to take the kind of buffeting it must have done several times during similar sorties.

The crew treated it all as a matter of course, getting on with their duties, checking radar and charts, communicating their information to headquarters in Miami, doing the other chores that seemed to keep everyone busy.

My notebook tells me we caught up with Hugo at 1:28 pm. For the next hour or so, I wondered why we ever tried--and I got the distinct impression almost everyone aboard wondered that too.

We were surrounded by clouds a dark gray, almost blue, color. The rain pelted down on the fuselage with an intensity that was deafening, like torrential rain on a galvanized roof and with a force that, it was later discovered, burst a small hole in the roof of the fuselage. When it was visible, the sea was almost black, like bubbling tar.

The computer print-out that had registered the wind speed from the time we took off peaked at 185 mph around this time.

We entered the eye--the area of low pressure that is completely calm and marks the centre of the hurricane--at an altitude of about 5,000 feet. Suddenly, my stomach seemed to become detached from my body as as the place dropped, I was told later, to 1,500 feet.

All hell seemed to break loose around and back of me. Briefcases, cups, soda-cans, books, anything unsecured came clattering down. The air conditioning shut down as did the radar and the weather computer. I just gripped the nearest arm and held on for dear life, realizing now why we had all been strapped in so tightly.

"That's unusual", flight engineer Steve Wade said when McKim and Genzlinger got back control of their plane. His attempt at sounding cool was father futile.

Dr. McFadden, a stocky man with gray beard and spectacles, came through, checking on us. He was visibly shaken.

"Everyone alright?" he inquired. We were but his face mirrored his concern when he told me: "This is the worst experience in all of our years going into a hurricane".

Soon there was to be even more. It was discovered that engine No. 3--the near right-side--had conked out. The pilots reported it was on fire and they had to shut it down. Another one was working but not at full capacity.

My life, I knew, rested in the skilled and experienced hands, and heads, of those in control of this wonderful piece of machinery. But, to tell the truth, I was never overcome by fear or panic. Somehow, I sensed all would be well.

Perhaps if I'd known more it would have been different, for we still had to find our way back out of the eye, to penetrate the wall again, and to gain elevation. To do that, on reduced power, meant jettisoning 7,000 of our 10,000 pounds of fuel to lighten the load and circling for an eternal hour while this was done.

Finally, a "weak spot" was found in the cloud formation and we could make an exit from the prison of the eye where we had been trapped for a frightening hour. Around us, winds were now registering 155 knots, and the plane was still being hammered by the weather.

But we were out of the eye and Dr. McFadden, in jubilant relief, exclaimed: "Let's get out of here". He echoed the feeling of everyone aboard.

The system engineer, Schricker ("that's it, don't worry about the first name", he said when I pressed) was more explicit. "I've been flying for 18 years and I don't think I want to fly again," he said.

As we got out of Hugo's clutches and left him to make his way towards the eastern Caribbean, Dr. McFadden put the experience in perspective for me. "You didn't really know what you went through," he said as we headed back to Grantley Adams, itching to back on Terra Firma. "We almost didn't get out of the eye. We almost didn't make it. It was a serious situation".

I believed him--and couldn't help wonder at the bravery of these men who so frequently risk their lives so that others may be saved from the destruction of the storms that head across the Atlantic annually between June and November.

They were working at Grantley Adams yesterday on getting that engine back into shape so that they could be ready the next time another one comes along.

They must be crazy!


Figure 3. An account of the September 15, 1989 flight through Hurricane Hugo posted by reporter Janice Griffith in the Barbados Sun newspaper.

Comments on Janice's story
The rain didn't really punch a hole the fuselage of our airplane as Janice reported. Also, we penetrated the eyewall at 1,500 feet, and dropped to 880 feet during the extreme turbulence in the eyewall. Other than that, Janice has the facts pretty well in hand, particularly the "They must be crazy!" part. Three of us--myself, radio operator Tom Nunn, and electronic engineer Terry Schricker--never flew again on a hurricane hunter mission. However, four members of that flight--Hurricane Field Program Manager Dr. Jim McFadden, Chief Systems Engineer Alan Goldstein, Navigator (now flight meteorologist) Sean White, and the director of NOAA's Hurricane Research Division, Frank Marks--continue to fly into hurricanes to this day.

I caught up with Janice Griffith via email last year, when I invited her to a "Hurricane Hugo survivors luncheon" for the twelve people from that flight who are still alive (alas, radio operator Tom Nunn, electronic engineer Neil Rain, and chief scientist Dr. Bob Burpee have passed on). Six of us got together at a hurricane conference in Orlando. Janice is still working as a reporter in Barbados, and couldn't make it. Her email to me:

"Nice Hearing from you.
Well after that trip into the eye of Hurricane Hugo,
I certainly will not be going on another.
We almost lost our lives.
And whenever I think about it...I just get some shivers".

Jeff Masters

Hurricane

The Atlantic is quiet; remembering Hurricane Hugo 20 years later

By: JeffMasters, 2:30 PM GMT on September 14, 2009

Considering that the third week of September is usually one of the busiest weeks for Atlantic hurricanes, the tropical Atlantic is very quiet today. The remains of Hurricane Fred continue to generate sporadic bursts of heavy thunderstorm activity over the middle Atlantic Ocean. Dry air and prohibitively high wind shear of 40 knots today will continue to prevent regeneration, and none of our reliable models are calling for Fred to regenerate this week.

Satellite imagery and this morning's QuikSCAT pass show a small circulation associated with a tropical wave about 100 miles south of the Cape Verdes Islands, just off the coast of Africa. The wave has only a small amount of heavy thunderstorms, on the west side of the circulation, and QuikSCAT showed only 20 mph winds in the region. None of the models develop this wave, and it is probably too small to develop into a tropical depression. Still, it is worth keeping an eye on.

Tropical storm development is possible this week along a frontal zone stretching from Florida to the waters between the Bahamas and North Carolina. However, wind shear will be relatively high in this region, and anything that develops may end up being extratropical in nature, and would likely move northeastward out to sea.

The GFS model is predicting development of a new tropical wave coming off the coast of Africa late this week.


Figure 1. The remains of Hurricane Fred (left) appears as a swirl of low-level clouds with a clump of heavy thunderstorm activity on the north side. A small tropical wave is near the Cape Verdes Islands, off the coast of Africa. This wave is probably too small to develop.

Twenty years ago on this date
On September 14, 1989, I arose at dawn to prepare for my flight to Barbados to meet Hurricane Hugo. First order of business was to flick on my weather radio and check out the latest advisory for the hurricane. Category 1, 90 mph winds, headed west-northwest at 15 mph. As expected. Next order of business, call in to the hurricane hunter hotline and listen to the mission plan. "We are planning a two-plane deployment to Barbados today, departing at twelve hundred hours. Crew assignments are as follows..." On schedule, and no crew changes. I finished packing my bag and headed to Miami International Airport to fly out to meet Hurricane Hugo.


Figure 2. GOES visible satellite image of Hurricane Hugo taken on September 14, 1989. Image credit: Google Earth rendition of the NOAA HURSAT data base.

As our big P-3 Orion hurricane hunter plane droned over the Caribbean towards Barbados, we didn't have any means to check on what the hurricane was doing. I could only guess how strong a hurricane might greet us when we landed. We landed uneventfully at Barbados' Grantley Adams International Airport shortly after dark, and disembarked from the aircraft. As we walked across the tarmac towards the terminal, we were suddenly confronted by the flashes of cameras as a group of reporters documented the arrival of the "daredevil" Hurricane Hunters. We'd never had a welcoming committee at one of our landings before, and all smiled and laughed at our sudden fame. It seems Hurricane Hugo was big news in the Caribbean. I quickly found out why, when I got to the weather briefing room at the terminal. Hugo had rapidly intensified during the day, and was now a major Category 3 hurricane with 115 mph winds. With Hugo still over a day from the islands, the hurricane had plenty of time to intensify further. Barbados was well south of the expected path of the hurricane, and was thus a safe base of operations, but the mood on the island was frightened and electric. It had been nine years since the last major hurricane smashed through the Lesser Antilles Islands--Hurricane Allen of 1980. The roll call of the most notorious hurricanes to devastate the islands of the Lesser Antilles--Allen of 1980, David of 1979, Inez of 1966, Cleo of 1964, Flora of 1963, and Donna of 1960--would soon be adding a new name.


Figure 3. The front page story of the September 15, 1989 issue of the Barbados Weekend Nation newspaper featured our arrival the night of September 14, 1989, at Barbados' Grantley Adams International Airport. From left to right: Alan Goldstein (electronic engineer), Dave Turner (pilot), Gerry McKim (pilot, partially hidden), Jim Roles (electronic engineer), Neal Rain (electronic engineer), Jeff Masters (flight meteorologist), Terry Schricker (electronic engineer), Sean White (Navigator), Lowell Genzlinger (pilot), Jack Parrish (flight meteorologist).

The entire Caribbean was in an uproar. Thousands of boats across the Caribbean set sail to seek safe harbor. Tourists besieged besieged airports, seeking to escape the hurricane. Stores throughout the Caribbean islands along Hugo's projected path reported shelves stripped of provisions as residents prepared for the Caribbean's most deadly fury--a fully mature Cape Verdes hurricane. And tomorrow, my plane with fourteen Hurricane Hunters and one reporter would be the first humans to encounter Hugo.

Tomorrow's post
By now, many of you have read my story of my flight into Hurricane Hugo on September 15, 1989. Tomorrow, I'll present the story of the flight as seen through the eyes of reporter Janice Griffith of the Barbados Sun.

Jeff Masters

Hurricane

Fred is dead; the Atlantic is quiet

By: JeffMasters, 1:16 PM GMT on September 13, 2009

Hurricane Fred is dead, thanks to strong wind shear that finished tearing the storm apart yesterday. While the remains of Fred have generated a burst of heavy thunderstorms this morning, prohibitively high wind shear of 40 - 50 knots today through Monday will prevent regeneration, and should be able to completely disrupt the remnant circulation of Fred.

A tropical wave about 200 miles southeast of the Cape Verdes Islands, just off the coast of Africa, remains disorganized. This morning's QuikSCAT pass showed an elongated circulation, and one spot of 45 mph winds in the small clump of heavy thunderstorms on the south side of the circulation. The wave is under about 20 knots of wind shear, and may show some slow development beginning Monday, when the shear should drop below 20 knots. NHC is giving this system a low (less than 30% chance) or developing into a tropical depression by Tuesday.

A low pressure system that was over the Texas Gulf of Mexico coast has moved inland, and is not a threat to develop into a tropical cyclone. Tropical storm development is possible this week along a frontal zone stretching from Florida to the waters between the Bahamas and North Carolina. However, wind shear will be relatively high in this region, and anything that develops may end up being extratropical in nature.


Figure 1. The remains of Tropical Storm Fred (left) appear as a swirl of low-level clouds with a clump of heavy thunderstorm activity on the north side. A new tropical disturbance near the coast of Africa is disorganized, due to 20 knots of wind shear.

Twenty years ago on this date
On September 13, 1989, Tropical Storm Hugo continued its westward march at 20 mph towards the Lesser Antilles Islands. Shortly after midnight on the 13th, satellite analysts at the National Hurricane Center noted a Central Dense Overcast (CDO) of thick cirrus clouds was forming over the center. The CDO was evidence that Hugo was beginning to build an eyewall. The thunderstorms in the eyewall were now powerful enough to lift large amounts of moisture 45,000 feet high, where the stable air of the stratosphere lay. Unable to penetrate into the stratosphere, the air lifted by Hugo's thunderstorms was forced to spread outward into a thick, circular layer of cirrus clouds--the CDO--that hid the storm's core. The mystery of what was happening beneath the Central Dense Overcast became apparent a few hours later, when a murky eye appeared. At 8 am EDT on the 13th, the National Hurricane Center upgraded Hugo to hurricane status.

At NOAA's Office of Aircraft Operations--the hurricane hunting division of NOAA--we busily prepared for tomorrow's deployment to Barbados of both of our P-3 Orion hurricane hunting aircraft. There were dropsondes and Air-Expendable Bathythermographs to load, computer checks to make, and calibration data to load. We chatted excitedly about the new hurricane that looked like an excellent case study for the hurricane scientists. But there was also an undercurrent of uneasiness to our cheerful preparations. We knew that a Cape Verdes-type hurricane like Hugo that was still 2 - 3 days from the Lesser Antilles would probably kill a lot of people--perhaps even close to home, here in Florida.

In a letter I wrote that night to my soon-to-be-fiancee, Diane, in Michigan, I said: "Well, that dark enveloping death feeling is back again, much stronger than before. I know Hugo the hurricane will kill people and I feel it coming close to here".


Figure 2. GOES visible satellite image of Hurricane Hugo taken on September 13, 1989. Image credit: Google Earth rendition of the NOAA HURSAT data base.

Jeff Masters


Hurricane

Fred dying; no immediate danger areas in the Atlantic

By: JeffMasters, 1:28 PM GMT on September 12, 2009

Tropical Storm Fred has been ripped apart by wind shear, as strong southerly winds of 20 knots have removed all of Fred's heavy thunderstorms, leaving only a naked low-level swirl of clouds. Wind shear of 20 - 40 knots will continue today through Monday, and Fred should dissipate by Sunday night. Due to the continued strong shear expected over Fred the next four days, it is unlikely there will be anything left of the storm to regenerate from once the remains reach an area with moderate wind shear five days from now.


Figure 1. Tropical Storm Fred (upper left) appears as a swirl of low-level clouds with no heavy thunderstorm activity in this morning visible satellite image. A new tropical disturbance (right) near the coast of Africa is disorganized, due to 20 - 30 knots of wind shear.

Elsewhere in the tropics
A large tropical wave that emerged from the coast of Africa Thursday is very disorganized. The wave as yet does not have much in the way of heavy thunderstorm activity associated with it, and wind shear is high, 20 - 30 knots. By Monday, the shear may drop below 20 knots, allowing some slow development. The GFS model has backed off on its prediction that this wave would develop into a tropical depression.

A low pressure system is over eastern Texas and the adjoining waters along the Texas Gulf of Mexico coast. This low is under high shear, about 25 knots, and is not tropical. Shear is expected to remain high, 20 - 30 knots, over the next five days. The low should remain non-tropical during this time, but will bring much-needed heavy rains to drought-stricken south Texas. Heavy rains in excess of five inches have occurred over portions of Texas, Oklahoma, and Louisiana from this low, and flash flood watches have been posted for a large sections of these states.

Over the next few days, we should also be alert for tropical storm development along a frontal zone stretching from the Gulf of Mexico waters offshore the western Florida coast, across the Florida Peninsula, to the waters between the Bahamas and North Carolina. However, wind shear will be relatively high in this region, and anything that develops may end up being extratropical in nature.


Figure 2. Total rainfall from the Austin, TX radar from the low pressure system over coastal Texas.

Twenty years ago on this date
On September 12, 1989, Tropical Storm Hugo, still far out at sea in the middle Atlantic, continued to grow more organized. Heavy thunderstorms thickened near the storm's center and in four prominent spiral bands. Updrafts from the intense thunderstorms near the storm's core began reaching the base of the stratosphere, creating high cirrus clouds that an upper-level anticyclone over the storm carried away. By nightfall, Hugo had intensified to a strong tropical storm with 65 mph winds. Now three days from the Lesser Antilles Islands, the storm continued to churn westward across the open Atlantic at 20 mph.

At NOAA's Miami-based Office of Aircraft Operations--the hurricane hunting division of NOAA--my boss, Jim McFadden, called me into his office. My fellow flight meteorologist, Jack Parrish, was also there. "We've got a planned two-plane deployment to Barbados on the 14th", Jim told us. "Frankly, if this storm wasn't named after the director of AOML, we wouldn't be going. It doesn't look too impressive right now." (AOML was NOAA's Atlantic Oceanographic and Marine Laboratory, which supervised research flights by NOAA's hurricane hunter aircraft, and Hugo Bezdek was the director). We discussed the possible missions, and agreed that regardless of Hugo's strength, we should be flying it, since we had used up very few of our allotted flight hours for the year. Jack and I would be in charge of coordinating the missions on the two aircraft. It would be my first hurricane flight of what had been a very slow season so far. I was excited to be going to Barbados, an island I had never been to. The as-yet unimpressive Tropical Storm Hugo did not give me any concerns about a possible rough ride.


Figure 3. AVHRR visible satellite image of Tropical Storm Hugo taken on September 12, 1989. Well-developed low-level spiral bands are apparent, and high cirrus clouds denoting upper-level outflow are visible on three sides. Image credit: Google Earth rendition of the NOAA HURSAT data base.

Jeff Masters

Hurricane

Outlook for the remainder of hurricane season

By: JeffMasters, 1:57 PM GMT on September 11, 2009

Hurricane Fred continues its slow decline, as wind shear of 25 knots tilts and stretches the storm, allowing dry air to penetrate into the hurricane core from the southwest side. With sea surface temperatures down near the threshold needed to support a tropical cyclone and wind shear expected to increase to 30 knots Saturday, Fred should continue to weaken the next few days. The storm's very slow motion will hasten this decay, since the storm will stir up cold waters from the depths that it will not be able to move away from. Fred will likely die by Tuesday.


Figure 1. Hurricane Fred (upper left) and a new tropical disturbance (right), newly emerged from the coast of Africa. At the time, Fred was a Category 1 hurricane with 85 mph winds.

Elsewhere in the tropics
A large tropical wave emerged from the coast of Africa last night and has a well-organized surface circulation, as seen on this morning's QuikSCAT pass. The wave as yet does not have much in the way of heavy thunderstorm activity associated with it, and wind shear is relatively high, about 20 knots. By Sunday, the shear will drop below 20 knots, and the wave may begin to develop. The GFS model predicts this will be a tropical depression by early next week.

A low pressure system is over eastern Texas and the adjoining waters along the Texas Gulf of Mexico coast. This low is under high shear, about 25 knots, and is not tropical. Shear is expected to remain high, 20 - 30 knots, over the next five days. The low should remain non-tropical during this time, but will bring much-needed heavy rains to drought-stricken south Texas. Flooding problems may also occur, and flash flood watches have been posted for six counties in extreme South Texas.

Early next week, we should be alert for tropical storm development along an old frontal zone stretching from the Florida Keys across the Florida Peninsula to the waters between the Bahamas and North Carolina. The NOGAPS model predicts development could occur on the Gulf side of Florida, and the GFS model forecasts that development is more likely on the east side of Florida.


Figure 2. Departure of Sea Surface Temperature (SST) from average for September 10, 2009, shows that SSTs were 0.5 - 1.0°C above average over most of the Main Development Region (MDR) for hurricanes in the Atlantic, from the coast of Africa to Central America, between 10°N and 20°N. Image credit: NOAA/NESDIS.

Outlook for the remainder of hurricane season
September 10 marks the halfway point of the Atlantic hurricane season, and the season has thus far been average to a bit below average. What, then, can we expect for the remainder of the season? First, let's take a look at Sea Surface Temperatures (Figure 2). SSTs are 0.5 - 1.0°C above average over most of the Main Development Region (MDR) for hurricanes in the Atlantic, from the coast of Africa to Central America, between 10°N and 20°N. This means that the ocean will be capable of supporting the development of major hurricanes well into the middle of October. Approximately 85% of all major hurricanes form in the Main Development Region.

Wind shear and El Niño
The current weak El Niño conditions in the tropical Eastern Pacific show no signs of weakening, and these El Niño conditions are likely contributing to the enhanced levels of wind shear observed over the Caribbean over the past month (Figure 3). However, wind shear has been near average over the remainder of the Main Development Region, which allowed two major hurricanes (Bill and Fred) to form in the region between Africa and the Lesser Antilles Islands. The latest 16-day forecast from the GFS model projects near-average wind shear levels across the Main Development Region for the remainder of September. The latest long range wind shear forecast from NOAA's CFS model predicts high levels of wind shear for the entire tropical Atlantic for the remainder of hurricane season--the typical pattern for an El Niño year. This model's September wind shear forecast doesn't look very accurate, so I mistrust the model's call for high wind shear for the remainder of hurricane season. It does not appear that this year's El Niño conditions are resulting in as much wind shear as a typical El Niño event generates over the tropical Atlantic. This may be because this year's El Niño conditions have some characteristics of a modiki El Niño. These "modiki" El Niños tend to have warming concentrated in the Central Pacific, instead of the Eastern Pacific. This year, the warming is greatest in the Eastern Pacific (see Figure 2), but there is also quite a bit of warming in the Central Pacific.


Figure 3. Departure of wind shear from average for the 31-day period August 9 - September 8, 2009. Wind shear has been above average over the Caribbean and Gulf of Mexico, and much below average over the Eastern Pacific--a typical pattern observed during El Niño years. Image credit: NOAA Climate Prediction Center.

Steering Currents
We've been lucky this year that the steering currents have aligned to keep our two major hurricanes, Bill and Fred, out to sea. This year's hurricane season has featured a very favorable steering current pattern, with an abnormal number of intense troughs of low pressure over the U.S. East Coast. These troughs have brought westerly winds far to the south, which have acted to recurve to the north all the tropical storms that have formed from African tropical waves. The latest 16-day forecast from the GFS model shows no change to this steering current pattern. It will remain difficult for tropical storms spawned from African tropical waves to make the long crossing of the Atlantic and impact the Caribbean, Bahamas, or Florida. The land areas at greatest risk of receiving strikes from hurricanes that develop from African tropical waves will continue to be Bermuda, North Carolina, New England, and the Canadian Maritime provinces.

Only one hurricane has made landfall this season--Category 1 Hurricane Bill, which did minimal damage to Newfoundland, Canada. Although it is an El Niño year, and the steering current pattern will continue to be favorable for keeping most of our storms out to sea, I expect we will get a hurricane strike somewhere in the Atlantic this season that will require a disaster response.

Twenty years ago on this date
On September 11, 1989, Tropical Depression Twelve continued to grow more organized, building a large region of heavy thunderstorms near its center. Two hooking spiral bands formed, prompting the National Hurricane Center to upgrade the depression to a tropical storm in their 11 am advisory. The new storm's name: Hugo. Tropical Storm Hugo continued to trek westward across the open Atlantic at 20 mph, still four days from the Lesser Antilles Islands.

That day at NOAA's Miami-based Office of Aircraft Operations--the hurricane hunting division of NOAA--we joked about the fearsome new storm with the same name as the director of NOAA's Atlantic Oceanographic and Marine Laboratory (AOML), Hugo Bezdek. AOML housed the offices of NOAA's Hurricane Research Division, whose scientists would decide whether or not our hurricane hunting group would intercept the new storm once it got close enough to the Lesser Antilles Islands. Even if Hugo was a dud, we figured we'd be flying the storm for sure, since it shared the same first name as the big boss of the hurricane research scientists.

After work that evening, I celebrated my 29th birthday by biking through the sun-dappled shaded streets of Coconut Grove. As I stopped to watch a perfect tropical fuchsia-red sunset, my thoughts roamed out over the eastern horizon. What kind of birthday present had the weather gods delivered me today? I was first on the list of flight meteorologists that would deploy to meet Hugo, should we fly the storm.


Figure 4. AVHRR visible satellite image of Tropical Storm Hugo taken on September 11, 1989. Image credit: Google Earth rendition of the NOAA HURSAT data base.

Jeff Masters

Hurricane

Fred fading; halfway point of hurricane season reached

By: JeffMasters, 1:40 PM GMT on September 10, 2009

Hurricane Fred peaked in intensity yesterday afternoon, attaining Category 3 strength with 120 mph winds. It is quite unusual to have such a powerful system so far east in the Atlantic, and Fred is only the third major hurricane to exist east of 35W. Fred is also the strongest hurricane so far south and east in the data record. However, this type of system would have been difficult to document before satellite pictures began in the 1960s.

Fred's glory is past, and the storm is on a downslide now, thanks to moderate wind shear of 15 - 20 knots and dry air eating into the hurricane's southwest side. The shear and the dry air will increase over the next few days, with the shear rising above 40 knots by Monday morning. Sea surface temperatures (SSTs) will also cool to near the 26.5°C threshold needed to sustain a tropical cyclone. The combination of high shear, dry air, and cool SSTs will likely kill Fred by Tuesday.


Figure 1. Hurricane Fred at peak strength, 8:55am EDT UTC 9/9/09. At the time, Fred was a Category 3 hurricane with 120 mph winds. Image credit: NASA.

Elsewhere in the tropics
An upper-level low pressure system has moved over Texas and is expected to spawn a surface low pressure system along the Texas Gulf of Mexico coast on Friday. This low will probably have characteristics of both a tropical and extratropical storm. The surface low is likely to move northeastward and move ashore near the Texas/Louisiana border region on Saturday or Sunday. There will be some high wind shear to the west of the low (shear is currently a high 25 knots), so it is uncertain whether this low will be capable of developing into a tropical cyclone. Regardless, this storm will bring heavy rain capable of causing flooding--and help alleviate the exceptional drought conditions over Southeast Texas.

Early next week, we should be alert for tropical storm development over the waters between the Bahamas and North Carolina, along an old frontal zone. None of the reliable models are forecasting tropical storm development in this area or in the Gulf of Mexico, though.


Figure 2. The climatological halfway point of the Atlantic hurricane season is today, September 10.

Halfway point of hurricane season
September 10 marks the halfway point of the Atlantic hurricane season. Despite a late start (Tropical Storm Ana did not form until August 15, the latest start to a hurricane season since 1992), our number of storms has been near average. An average Atlantic hurricane season has 5 named storms, 3 hurricanes, and 1 intense hurricane by the midpoint of the season. So far this year, we've had 6 named storms, 2 hurricanes, and 2 intense hurricanes. A better measure of hurricane activity that takes into account their destructive power is the Accumulated Cyclone Energy (ACE) index. ACE for an individual storm is computed by squaring the maximum sustained winds of the storm at each 6-hourly advisory, and summing up over the entire lifetime of the storm. As of 5am EDT this morning, the seasonal ACE tally was 37.5. This number should rise to around 40 by the end of the day, thanks to the presence of Hurricane Fred. Over the period 1950 - 2005, the average ACE index for a half-season was 51, so 2009 ranks about 20% below average for the halfway point of the season. But when compared to the hurricane seasons we've been having since the current active hurricane period began in 1995, this year has been quite inactive. Between 1995 and 2008, the average ACE index for the halfway point of the season was 72. Thus, 2009 is about 45% less active than what we've been accustomed to over the past 14 years.

We've been lucky this year that the steering currents have aligned to keep our two major hurricanes, Bill and Fred, out to sea. What will the rest of the season have in store for us? I'll present an analysis on Friday.

Twenty years ago on this date
On September 10, 1989, the strong tropical wave that had moved off the coast of Africa the previous day acquired an organized circulation at the surface and began building a concentrated area of heavy thunderstorms near its center. A new tropical depression, the 12th of the season, was born. Moving westward at 20 mph, the depression brought strong, gusty winds and heavy rain showers to the Cape Verdes Islands as it passed to the south. Forecasters at the National Hurricane Center predicted that the steadily organizing tropical depression would strengthen into a tropical storm within the next day or two. The next name on the list of Atlantic tropical storm names for 1989: Hugo.


Figure 3. AVHRR visible satellite image of Tropical Depression Twelve taken on September 10, 1989. Image credit: Google Earth rendition of the NOAA HURSAT data base.

Jeff Masters

Hurricane

Fred rapidly intensifies; new wunderground storm surge section launched

By: JeffMasters, 1:51 PM GMT on September 09, 2009

Hurricane Fred put on an impressive burst of intensification overnight, and is now a major Category 3 hurricane with 120 mph winds. However, Fred is not a threat to any land areas for at least the next week. Satellite imagery of Fred shows the spectacular signature of a classic Cape-Verdes type major hurricane, with a prominent eye, well-developed low-level spiral bands, and high cirrus clouds denoting excellent upper-level outflow on three sides. It is quite unusual to have such a powerful system so far east in the Atlantic, and Fred is only the third major hurricane to exist east of 35W. Fred is also the strongest hurricane so far south and east in our data record. However, this type of system would have been difficult to document before satellite pictures began in the 1960s.


Figure 1. Visible satellite image of Hurricane Fred at 10:30am EDT 9/9/09. Fred was a Category 3 (120 mph winds) at this time.

The forecast for Fred
Wind shear through Thursday morning is expected to stay in the low range, 5 - 10 knots, and ocean temperatures will be about 1 - 2°C above the threshold needed for tropical cyclone formation. Given these conditions, plus such factors as the temperature at 200 mb and the amount of moisture between 700 mb and 500 mb, this morning's run of the SHIPS model computes that the Maximum Potential Intensity (MPI) Fred can reach tonight is 140 mph (121 knots), which would make it a Category 4 hurricane. This is the strongest a hurricane can get in this region of the atmosphere. Very few hurricanes ever reach their MPI, and it will be interesting to see how close Fred gets to this mark.

Shear will rise to the moderate range, 15 - 20 knots, Thursday through Friday, then increase to the high range, 20 - 40 knots, Saturday through Sunday, thanks to a strong trough of low pressure traversing the North Atlantic. This should weaken Fred to a tropical storm five days from now. The trough will also pull Fred to the northwest and then north. Most of the models foresee that this trough will not be strong enough to fully recurve Fred to the northeast and out to sea. However, another strong trough of low pressure is forecast to traverse the central Atlantic about eight days from now, and this trough should be strong enough to recurve the storm northeastward out to sea. The odds of Fred making it all the way across the Atlantic to threaten land areas appear low at this time.

Elsewhere in the tropics
A weak front is expected to move off the Texas coast Friday and linger along the coast for several days. Beginning on Friday, we will need to watch the Western Gulf of Mexico for possible development of a tropical cyclone along this front. Any storm that develops would likely move northeast or north-northeast and impact Louisiana and northern Texas coast. The models are less enthusiastic this morning about developing such a storm than they were in previous runs, and there will be some high wind shear to the west for a potential tropical system to contend with.

New wunderground storm surge section launched
The Weather Underground is pleased to announce the release of the Internet's most comprehensive hurricane storm surge web pages. The new storm surge section provides more than 500 detailed, zoomed-in storm surge maps from the official storm surge model used by the National Hurricane Center--the Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model. I've created SLOSH model worst-case flood maps for Category 1, 2, 3, 4, and 5 hurricanes for the entire U.S. Atlantic coast, plus Hawaii, Puerto Rico, the Virgin Islands, and the Bahamas. Zoom-in maps of fifteen important cities such as Miami, New York City, Boston, Tampa, and Corpus Christi are included. To help coastal residents see how past storms have affected their region, the wunderground storm surge pages also include SLOSH model animations of the surge for more than 40 historic storms--from the Great Colonial Hurricane of 1635 to Hurricane Ike of 2008. You can access the new storm surge web pages.from our Tropical/Hurricane page, on the right side of the page under my blog box. I encourage all coastal residents along the U.S. coast to take the time to familiarize themselves with the storm surge risk where they live.


Figure 2. Sample water depth inundation image (left) and storm tide image (right), created using NOAA's SLOSH model. These Maximum of the "Maximum Envelope of Waters" (MOM) plots are for Tampa Bay, Florida, for a mid-strength Category 4 hurricane (sustained winds of 143 mph) hitting at high tide.

How to interpret the storm surge images
There are two sets of images available. The first set, titled "Maximum Water Depth", shows the water depth at each grid cell of the SLOSH domain. Thus, if you are inland at an elevation of ten feet above mean sea level, and the combined storm surge and tide (the "storm tide") is fifteen feet at your location, the water depth image will show five feet of inundation. The second set of images, titled "Maximum Storm Tide", shows how high above mean sea level the sum of the storm surge plus the tide reaches. Over the ocean, the storm tide and water depth images will show the same values. The storm tide images contain no information about how deep the water will be inland, and are generally less useful than the water depth images. All of these Maximum of the "Maximum Envelope of Waters" (MOM) images were generated for high tide, and thus show worst-case inundation scenarios for mid-strength hurricanes of each Saffir-Simpson Category (Category 1, 2, 3, 4, and 5). Category 5 hurricanes have never occurred in the Mid-Atlantic or New England regions, so there are no Category 5 images shown there. No single storm will be able to cause the level of flooding depicted in the SLOSH storm surge images along the entire coast. A sample set of storm surge images for a Category 4 hurricane hitting Tampa Bay is shown in Figure 2. Black lines mark the coastline, and also delineate the grid the SLOSH model used. There may be storm surge present outside the boundaries of the grid, so pay attention to where the grid boundaries are. Also, if you see a high surge modeled for a narrow waterway that goes right up to the edge of the grid boundary, don't believe it. The model puts an artificial barrier at the grid boundary, and the surge is piling up against this non-existent barrier. Empty brownish grid cells with no coloration show where no inundation is computed to occur. St. Petersburg becomes two islands in a worst-case scenario Category 4 hurricane, as shown by the brown areas surrounded by colored areas of storm tide (this did occur during the Great Gale of 1848, a Category 4 hurricane that hit the city). The tide level is marked at the bottom of the color legend, and is 1 foot in this example. The left "maximum water depth" image shows how high above each grid cell the storm tide reaches. The storm tide--the combination of the storm surge plus the 1 foot high tide--reaches as much as 27 feet above mean sea level (pink colors) near downtown Tampa (right-hand "maximum storm tide" image). The amount of inundation inland is controlled by the elevation of the land. Some of the inland regions near downtown Tampa being inundated by the 27-foot storm tide are at an elevation of 19 feet, so as much as 8 feet of inundation will occur at those locations (dark blue colors in the left-hand "maximum water depth" image). Interstate highways are the thick grey-green lines, and smaller highways are shown as dark green and light green lines. If a road is inundated by storm surge, it will not appear. County boundaries are shown in red.

Twenty years ago on this date
On September 9, 1989, satellite imagery detected a strong tropical wave with plenty of spin and heavy thunderstorm activity moving off the coast of Africa, just south of the Cape Verdes Islands. The satellite analyst at the National Hurricane Center duly noted the tropical wave, the 35th such wave to move off Africa that year, in his tropical weather discussion. No one could suspect that the routine-looking tropical wave would eventually grow to become Hurricane Hugo--the costliest Atlantic hurricane of all time.

Jeff Masters

Hurricane

Fred is born; storm surge survival misconceptions

By: JeffMasters, 1:29 PM GMT on September 08, 2009

Tropical Storm Fred sprang to life yesterday off the coast of Africa, but is not a threat to any land areas for at least the next week. Satellite imagery from the European satellite shows a well-organized circulation with plenty of low-level spiral bands and high cirrus clouds streaming away from the storm at high levels, indicating good upper level outflow. There is dry air of the Saharan Air Layer to the north of Fred, but it is far enough away so as not to be a major impediment to development. Wind shear is moderate, 10 - 15 knots, and ocean temperatures are 1 - 2°C above the threshold needed for tropical cyclone formation.


Figure 1. Morning satellite image of Fred, off the coast of Africa. Note the layer of low stratocumulus clouds to Fred's north, a sign of relatively dry, stable air there.

The forecast for Fred
Wind shear this afternoon is expected to drop to the low range, 5 - 10 knots, and continue to remain low until Thursday morning, when it will rise to the moderate range again. Given Fred's current improving appearance, the storm should be able to attain hurricane status by Thursday. At that time, a strong trough of low pressure traversing the North Atlantic will bring higher shear, weakening the storm. The trough will also pull Fred to the northwest and then north. Most of the models foresee that this trough will not be strong enough to fully recurve Fred to the northeast and out to sea. However, with the steering pattern for this year continuing to feature plenty of deep troughs of low pressure moving off the U.S. East Coast, the odds of Fred making it all the way across the Atlantic to threaten land areas appear low at this time.

Elsewhere in the tropics
An area of concentrated thunderstorms has developed off the North Carolina coast in association with the remains of an old cold front. This system is under about 20 - 30 knots of shear, and is not tropical. However, it will bring heavy rain to eastern North Carolina and Virginia today and Wednesday, as the storm slides north-northeastward along the coast.

A strong low pressure system is expected to move into the central U.S. by this weekend, dragging a cold front into the western Gulf of Mexico. In several of their runs over the past few days, the GFS and ECMWF models have been predicting a tropical system may develop along this front in the western Gulf of Mexico by Sunday or Monday. The latest GFS phase space analysis of the predicted storm confirms that this would be a tropical cyclone, and not extratropical. There is currently not an area of disturbed weather in the Gulf, but we will have to keep an eye out there beginning this weekend, when the front moves offshore.

I'll have an update Wednesday, when I'll also announce the release of wunderground's excellent new series of storm surge pages. The new storm surge section provides more than 500 detailed, zoomed-in storm surge maps from the official storm surge model used by the National Hurricane Center--the Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model. The Weather Underground has created SLOSH model worst-case flood maps for Category 1, 2, 3, 4, and 5 hurricanes for the entire U.S. Atlantic coast, plus Hawaii, Puerto Rico, the Virgin Islands, and the Bahamas. Zoom-in maps of fifteen important cities such as Miami, New York City, Boston, Tampa, and Corpus Christi are included. To help coastal residents see how past storms have affected their region, the wunderground storm surge pages also include SLOSH model animations of the surge for more than 30 historic storms--from the Great Colonial Hurricane of 1635 to Hurricane Ike of 2008. Included here is one section from the new storm surge pages, "Storm Surge Survival Misconceptions".

Storm Surge Survival Misconceptions
The storm surge is usually the most dangerous threat of a hurricane. The ten deadliest U.S. hurricane disasters, including the Galveston Hurricane of 1900 (8000 killed), the Lake Okeechobee Hurricane of 1928 (2500 killed), and Hurricane Katrina of 2005 (1833 killed), were all primarily storm surge disasters. The Biloxi-Gulfport Sun Herald ran a series of stories in 2005 on people who were lucky enough to survive Hurricane Katrina's record storm surge. There were some common misconceptions that were touched on in these stories, and are reproduced here from Margie's Kieper's blog on the Hurricane Katrina storm surge.


Figure 2. A man wearing a tiny life jacket and clutching a neon green noodle and a pet dog floats on the remains of a house in Waveland, MS, during Hurricane Katrina. The photo was taken from the second floor window of a home, and the water is close to the roof line of the first floor. The home was at an elevation of about 17 feet, and the surge is close to ten feet deep here. There are electric lines running down from a pole to a home from left to right. In the distance on the right is a home with water up to the roof line. The eye is probably overhead, as the water is relatively calm and there appears to be little wind or rain, even though the pine trees are bent from the recent force of the eyewall winds. The photo was taken by Judith Bradford. Her husband, Bill Bradford, swam out and rescued the man and his dog, and two other people who floated by. He reported that the water was nothing like white water, but was a gentle, continuous flow. He was lucky. In the nearby Porteaux Bay area, a woman watched her fiance get pulled from a tree by the force of the current. The man was washed out into the Gulf and drowned. The image above is described in more detail on Margie Kieper's Katrina storm surge web page.

Misconception: Call 911 and you can be rescued, while the water is pouring into your home.
How? No one will be able to get to you. Water rises quickly--sometimes six to ten feet within minutes; cars can't drive in it, and it is usually unnavigable by boats when it is coming ashore.

Misconception: Just stuff towels under the door jambs. Then rush around to start picking up things that are close to floor level, so you can save them.
Bad idea. In a minute or so the surge will burst open the door, and instead of standing in a room with four inches of water, you'll be knocked off your feet and into whatever piece of furniture is closest, and will suddenly be in three or four feet of moving water that you can't make any headway into...just before the refrigerator, quickly rushing through the water towards you, knocks you cold.

Misconception: You'll be able to maneuver around in the rushing water.
Probably not. Some people who drowned were not even able to get out of the room they were in, when the water started pouring into the home. The speed of water in surge can be equivalent to a Class III or IV rapids (Class V is hardly navigable by expert kayakers and canoers, and Class VI is not navigable at all).

Misconception: You'll know in time.
The surge is usually not a wall of water as is often assumed, but rather a rapid rise of water of several feet over a period of minutes. It can sneak in unexpectedly, on little cat feet. Most people that were not completely taken by surprise simply happened to look out the window at the right time.

Misconception: You can outrun the storm surge in your car.
Here's an email I got last year from a resident in the Florida Keys who ignored the evacuation order for Hurricane Ike in 2008: I hate to bother you again, but we live on Marathon in the Florida Keys on the Atlantic side, and my husband says that if we see water coming up from storm surge and have an inch of water in our house, that we can outrun the storm surge in our car. Can you please tell me if there is any way this can possibly be true? P.S., I don't know of anyone who lives down here who is planning on evacuating for Ike. Everyone says they are staying. If you wait until the water is an inch high before trying to outrun the surge, the odds are that the surge will rise to over a foot high before you get your car out of the driveway. If the water is a foot high, the typical 10 - 15 mph speed of the storm surge's current has enough force to sweep a car away. In many places along the coast, there is only one road out of a low-lying region prone to storm surges, and the surge will cut off one's only escape route. The Keys have only one road, and the storm surge will likely be moving perpendicular to the road, cutting off the only escape route. One of these days, there are going to be a lot of people who fail to evacuate caught and killed in the Keys by the storm surge from a major hurricane.

How to Survive a Storm Surge
People who survived Katrina's storm surge did one of several things: they floated out an open window, and managed to hang onto debris, a tree, or some other structure above the water, until the surge receded, hours later. Or, they were able to pull themselves into an attic, or make it up to a second floor, where water did not reach, and luckily the home was not swept away. It is common in many flood-prone regions behind levees to keep an axe fastened to the wall of the attic. Then, if water comes in unexpectedly, you can get into the attic and chop a hole through the roof to escape. Don't forget to keep a length of rope there that you can use to tie yourself to a sturdy part of the house (don't tie yourself to the steel beams of the house, as these will sink).

The best way to survive a storm surge is to heed evacuation orders and leave before the surge arrives!

Storm Surge Safety Actions
- Minimize the distance you must travel to reach a safe location; the further you drive the higher the likelihood of encountering traffic congestion and other problems on the roadways.

- Select the nearest possible evacuation destination, preferably within your local area, and map out your route. Do not get on the road without a planned route, or a place to go.

- Choose the home of the closest friend or relative outside a designated evacuation zone and discuss your plan with them before hurricane season.

- You may also choose a hotel/motel outside of the vulnerable area.

- If neither of these options is available, consider the closest possible public shelter, preferably within your local area.

- Use the evacuation routes designated by authorities and, if possible, become familiar with your route by driving it before an evacuation order is issued.

- Contact your local emergency management office to register or get information regarding anyone in your household whom may require special assistance in order to evacuate.

- Prepare a separate pet plan; most public shelters do not accept pets.

- Prepare your home prior to leaving by boarding up doors and windows, securing or moving indoors all yard objects, and turning off all utilities.

- Before leaving, fill your car with gas and withdraw extra money from the ATM.

- Take all prescription medicines and special medical items, such as glasses and diapers.

- If your family evacuation plan includes an RV, boat or trailer, leave early. Do not wait until the evacuation order or exodus is well underway to start your trip.

- If you live in an evacuation zone and are ordered to evacuate by state or local officials, do so as quickly as possible. Do not wait or delay your departure, to do so will only increase your chances of being stuck in traffic, or even worse, not being able to get out at all.

- Expect traffic congestion and delays during evacuations. Expect and plan for significantly longer travel times than normal to reach your family's intended destination.

- Stay tuned to a local radio or television station and listen carefully for any advisories or specific instructions from local officials. Monitor your NOAA Weather Radio.

Source: NOAA

Jeff Masters

Hurricane

New African disturbance 96L likely to develop

By: JeffMasters, 2:55 PM GMT on September 07, 2009

A tropical wave (96L) that emerged off the coast of Africa yesterday has organized rather quickly, and will likely become a tropical depression by Tuesday night. Satellite imagery from the European satellite shows a well-organized circulation, but not enough heavy thunderstorm activity near the center of circulation to be considered a tropical depression. The storm is far enough south that the dry air of the Saharan Air Layer is not a major impediment to development. Wind shear is moderate, 10 - 15 knots, and ocean temperatures are 1 - 2°C above the threshold needed for tropical cyclone formation.


Figure 1. Morning satellite image of 96L, off the coast of Africa. The remains of disturbance 95L, which are under 30 - 40 knots of wind shear, can be seen at upper left.

The forecast for 96L
Most of the models develop 96L, and the chances are that this disturbance will become Tropical Storm Fred later this week. The system will initially move west-northwest, but by Thursday, a strong trough of low pressure passing to 96L's north will pull the storm to the northwest, and may be capable of fully recurving the storm to the northeast. However, most of the models foresee that 96L will not move far enough north for this to happen, and that the storm will have to wait for the next trough of low pressure. With the steering pattern for this year continuing to feature plenty of deep troughs of low pressure moving off the U.S. East Coast, the odds of 96L making it all the way across the Atlantic to threaten land areas appear low. Still, much that is unexpected can and does happen in the world of tropical meteorology, and 96L bears watching.

North Carolina low
An area of concentrated thunderstorms has developed off the North Carolina coast in association with the remains of an old cold front. This system is under about 20 - 30 knots of shear, and is not tropical. However, it will bring heavy rain to eastern North Carolina today and Tuesday, as the storm slides north-northeastward along the coast.

I'll have an update Tuesday.

Jeff Masters

Hurricane

The tropics are quiet

By: JeffMasters, 1:11 PM GMT on September 06, 2009

Considering that this is historically the peak week of the Atlantic hurricane season, the tropics are quiet. There is an area of disturbed weather in the middle Atlantic (95L) that NHC has been mentioning in their Tropical Weather Outlook the past day, but this disturbance is entering a region of high wind shear and is not a threat to develop.

A strong tropical wave with plenty of rotation is emerging off the coast of Africa this morning, and this wave is a good candidate to show some development this week as it heads west-northwest over the Atlantic. The wave is under about 15 knots of wind shear, and is being developed by several models, including the GFS and ECMWF. However, the models show that this new wave will be pulled northwestward by a strong trough of low pressure this week, and it appears unlikely that the wave will make the long crossing of the Atlantic necessary to threaten any land areas. Another wave with plenty of spin will emerge from the coast of Africa two days from now, and will also have a chance to develop.


Figure 1. Morning satellite image of 95L and a new tropical wave with potential to develop, emerging from the coast of Africa.

An area of concentrated thunderstorms has developed off the North Carolina coast in association with the remains of an old cold front. This system is under about 20 - 30 knots of shear, and is not tropical. However, it will bring heavy rain just offshore of North Carolina's Outer Banks today as it slides north-northeastward along the coast.

I'll have an update Monday.

Jeff Masters

Hurricane

Arctic temperatures the warmest in 2,000 years; 2009 Arctic sea ice loss 3rd highest

By: JeffMasters, 2:32 PM GMT on September 04, 2009

It's time to take a bit of a break from coverage of the Atlantic hurricane season of 2009, and report on some important climate news. The past decade was the warmest decade in the Arctic for the past 2,000 years, according to a study called "Recent Warming Reverses Long-Term Arctic Cooling" published today in the journal Science. Furthermore, four of the five warmest decades in the past 2,000 years occurred between 1950 - 2000, despite the fact that summertime solar radiation in the Arctic has been steadily declining for the past 2,000 years. Previous efforts to reconstruct past climate in the Arctic extended back only 400 years, so the new study--which used lake sediments, glacier ice cores, and tree rings to look at past climate back to the time of Christ, decade by decade-- is a major new milestone in our understanding of the Arctic climate. The researchers found that Arctic temperatures steadily declined between 1 A.D. and 1900 A.D., as would be expected due to a 26,000-year cycle in Earth's orbit that brought less summer sunshine to the North Pole. Earth is now about 620,000 miles (1 million km) farther from the Sun in the Arctic summer than it was 2000 years ago. However, temperatures in the Arctic began to rise around the year 1900, and are now 1.4°C (2.5°F) warmer than they should be, based on the amount of sunlight that is currently falling in the Arctic in summer. "If it hadn't been for the increase in human-produced greenhouse gases, summer temperatures in the Arctic should have cooled gradually over the last century," Bette Otto-Bliesner, a co-author from the National Center for Atmospheric Research, said in a statement.

The Arctic melt season of 2009
Arctic sea ice suffered another summer of significant melting in 2009, with August ice extent the third lowest on record, according to the National Snow and Ice Data Center. August ice extent was 19% below the 1979 - 2000 average, and only 2007 and 2008 saw more melting of Arctic sea ice. We've now had two straight years in the Arctic without a new record minimum in sea ice. However, this does not mean that the Arctic sea ice is recovering. The reduced melting in 2009 compared to 2007 and 2008 primarily resulted from a different atmospheric circulation pattern this summer. This pattern generated winds that transported ice toward the Siberian coast and discouraged export of ice out of the Arctic Ocean. The previous two summers, the prevailing wind pattern acted to transport more ice out of the Arctic through Fram Strait, along the east side of Greenland. At last December's meeting of the American Geophysical Union, the world's largest scientific conference on climate change, J.E. Kay of the National Center for Atmospheric Research showed that Arctic surface pressure in the summer of 2007 was the fourth highest since 1948, and cloud cover at Barrow, Alaska was the sixth lowest. This suggests that once every 10 - 20 years a "perfect storm" of weather conditions highly favorable for ice loss invades the Arctic. The last two times such conditions existed was 1977 and 1987, and it may be another ten or so years before weather conditions align properly to set a new record minimum.

The Northeast Passage opens
As a result of this summer's melting, the Northeast Passage, a notoriously ice-choked sea route along the northern Russia, is now clear of ice and open for navigation. Satellite analyses by the University of Illinois Polar Research Group and the National Snow and Ice Data Center show that the last remaining ice blockage along the north coast of Russia melted in late August, allowing navigation from Europe to Alaska in ice-free waters. Mariners have been attempting to sail the Northeast Passage since 1553, and it wasn't until the record-breaking Arctic sea-ice melt year of 2005 that the Northeast Passage opened for ice-free navigation for the first time in recorded history. The fabled Northwest Passage through the Arctic waters of Canada has remained closed this summer, however. An atmospheric pressure pattern set up in late July that created winds that pushed old, thick ice into several of the channels of the Northwest Passage. Recent research by Stephen Howell at the University of Waterloo in Canada shows that whether the Northwest Passage clears depends less on how much melt occurs, and more on whether multi-year sea ice is pushed into the channels. Counter-intuitively, as the ice cover thins, ice may flow more easily into the channels, preventing the Northwest Passage from regularly opening in coming decades, if the prevailing winds set up to blow ice into the channels of the Passage. The Northwest Passage opened for the first time in recorded history in 2007, and again in 2008. Mariners have been attempting to find a route through the Northwest Passage since 1497.


Figure 1. Sea ice extent on September 2, 2009, with the Northwest Passage (red line) and Northeast Passage (green line) shown. The Northeast Passage was open, but the Northwest Passage was blocked in three places. The orange line shows the median edge of sea ice extent for September 2 during the period 1979 - 2000, and this year's ice extent is about 19% below average. Image credit: National Snow and Ice Data Center.

Commercial shipping begins in the Northeast Passage
This year's opening marks the fourth time in five years that the Northeast Passage has opened, and commercial shipping companies are taking note. Two German ships set off on August 21 on the first commercial voyage ever made through the Northeast Passage without the help of icebreakers. The Northeast Passage trims 4,500 miles off the 12,500 mile trip through the Suez Canal, yielding considerable savings in fuel. The voyage was not possible last year, because Russia had not yet worked out a permitting process. With Arctic sea ice expected to continue to decline in the coming decades, shipping traffic through the Northeast Passage will likely become commonplace most summers.

When was the Northeast Passage ice-free in the past?
People have been attempting to penetrate the ice-bound Northeast Passage since 1553, when British explorer Sir Hugh Willoughby attempted the passage with three ships and 62 men. The frozen bodies of Sir Hugh and his men were found a year later, after they failed to make it past the northern coast of Finland. British explorer Henry Hudson, who died in 1611 trying to find a route through Canada's fabled Northwest Passage, (and whom Canada's Hudson Bay and New York's Hudson River are named after), attempted to sail the Northeast Passage in 1607 and 1608, and failed. The Northeast Passage has remained closed to navigation, except via assist by icebreakers, from 1553 to 2005. The results published in Science today suggest that prior to 2005, the last previous opening was the period 5,000 - 7,000 years ago, when the Earth's orbital variations brought more sunlight to the Arctic in summer than at present. It is possible we'll know better soon. A new technique that examines organic compounds left behind in Arctic sediments by diatoms that live in sea ice give hope that a detailed record of sea ice extent extending back to the end of the Ice Age 12,000 years ago may be possible (Belt et al., 2007). The researchers are studying sediments along the Northwest Passage in hopes of being able to determine when the Passage was last open.

References
Belt, S.T., G. Masse, S.J. Rowland, M. Poulin, C. Michel, and B. LeBlanc, "A novel chemical fossil of palaeo sea ice: IP25", Organic Geochemistry, Volume 38, Issue 1, January 2007, Pages 16-27.

Darrell S. Kaufman, David P. Schneider, Nicholas P. McKay, Caspar M. Ammann, Raymond S. Bradley, Keith R. Briffa, Gifford H. Miller, Bette L. Otto-Bliesner, Jonathan T. Overpeck, Bo M. Vinther, and Arctic Lakes 2k Project Members, 2009, "Recent Warming Reverses Long-Term Arctic Cooling", Science 4 September 2009: 1236-1239.

Howell, S. E. L., C. R. Duguay, and T. Markus. 2009. Sea ice conditions and melt season duration variability within the Canadian Arctic Archipelago: 1979.2008, Geophys. Res. Lett., 36, L10502, doi:10.1029/2009GL037681.

Tropical Weather Outlook
The remains of Tropical Storm Erika are bringing heavy rain to Puerto Rico and the Virgin Islands today, and this activity will spread to the Dominican Republic on Saturday. Radar-estimated rainfall shows up to three inches of rain has fallen in eastern Puerto Rico from the storm. Long range radar out of Puerto Rico shows no surface circulation or organization of the echoes, and redevelopment of Erika over the next three days is unlikely to occur due to high wind shear of 25 - 30 knots. By Monday or Tuesday, shear may drop enough to allow redevelopment, depending upon the location of Erika's remains. Redevelopment is more likely if Erika works its way northwestward into the Bahamas.

A large tropical wave with plenty of spin is located a few hundred miles southwest of the Cape Verdes Islands, off the coast of Africa. Heavy thunderstorm activity has increased slightly in this wave over the past day, and it has the potential to gradually develop into a tropical depression by early next week. NHC is giving this wave a low (less than 30% chance) of developing into a tropical depression by Sunday. The GFS model continues to predict development of this wave into a tropical depression early next week.

I'll have an update Saturday or Sunday, depending upon developments in the tropics.

Jeff Masters

Climate Change Sea Ice

Erika steadily weakening

By: JeffMasters, 7:43 PM GMT on September 03, 2009

Tropical Storm Erika has weakened steadily this afternoon, and has not generated any sustained winds of tropical storm force (39 mph) at any weather stations in the Lesser Antilles Islands today, according to our wundermap for the region. Erika has dumped some heavy rain on the islands, with 8.03" of rain measured on Dominica over the past two days. The Hurricane Hunters are in the storm now, and have thus far found top winds of 36 mph at the surface and at their flight level of 1000 feet. Radar animations out of Martinique show that the areal coverage and intensity of rain echoes has diminished greatly since this morning, and IR satellite loops also show a major decrease in heavy thunderstorm activity. Visible satellite images (Figure 1) show that the low-level center has become exposed to view, and there is very little heavy thunderstorm activity near Erika's center. Erika is probably just a tropical depression now.


Figure 1. Visible satellite image of Erika showing the exposed swirl of its low-level center southeast of Puerto Rico.

The forecast for Erika
Erika is headed west, in defiance of most of the computer models that predicted a northwest or west-northwest track. Regardless, Erika's track will take the storm into a band of significantly higher wind shear of 25 - 35 knots, Friday through Saturday. Considering that Erika is steadily weakening and is barely alive now, the storm should dissipate by Saturday, and perhaps much sooner. Erika's remains will still be capable of dumping very heavy rains of 3 - 5 inches over the Dominican Republic, Puerto Rico, and the northern Lesser Antilles Islands, and 1 - 3 inches over Haiti and the Southeast Bahamas over the next few days. However, the recent decrease of Erika's heavy thunderstorms makes lower rainfall totals more probable. By Monday, when the remains of Erika should have penetrated through the band of high wind shear over the Greater Antilles, shear may fall low enough to allow redevelopment. This is a scenario offered by the NOGAPS and GFS models. The other models predict quite a bit more shear in the region, and I believe any redevelopment of Erika early next week is unlikely. The GFDL and HWRF models continue to insist that Erika will head northwest, brush off the high shear, and intensify into a Category 2 hurricane five days from now.

McAfee virus alert messages
A number of wunderground users with the McAfee virus protection software installed were alerted yesterday that a possible Trojan virus existed on our web pages. After an investigation of the issue, we have determined that this is a false alarm. It appears McAfee updated their virus files yesterday, and included in their list of suspected viruses JavaScript web pages that compressed using the packer compression system used by wunderground. We've changed the compression technique used on our web pages, and hopefully this will eliminate the bogus McAfee alert messages.

Elsewhere in the Atlantic
A large, strong tropical wave with plenty of spin emerged from the coast of Africa this morning. The wave is not yet generating much in the way of heavy thunderstorms, but has the potential to gradually develop into a tropical depression by early next week. NHC is giving this wave a low (less than 30% chance) of developing into a tropical depression by Saturday. The GFS model continues to predict development of this wave into a tropical depression early next week.

I'll have an update Friday.

Jeff Masters

Hurricane

Erika dumping heavy rain on the Lesser Antilles

By: JeffMasters, 2:12 PM GMT on September 03, 2009

Tropical Storm Erika is hanging together despite strong wind shear, and is bringing high winds and much-needed heavy rain to the Lesser Antilles Islands. Winds on the south shore of Dominica Island were sustained at 37 mph this morning, and 8.03" of rain have been measured at the airport over the past two days. Winds and rain at nearby islands have been less, according to our wundermap for the region. The Hurricane Hunters are in the storm now, and have generally encountered top winds of 40 - 45 mph at the surface. They did find one spot of 50 - 65 mph winds, but that was likely due to outflow from a strong thunderstorm, and is not representative of Erika's wind field.


Figure 1. Radar image of Tropical Storm Erika at 9:15am EDT 9/3/09. Image credit: Meteo France.

Erika has improved in organization a bit since last night, but remains weak and disorganized, thanks to about 20 knots of shear at the 200 mb level, as seen on last night's Guadeloupe upper air sounding. Radar animations out of Martinique show plenty of heavy rain moving through the Lesser Antilles, but little organization of the echoes. Satellite imagery shows no low-level spiral bands and little upper-level outflow. Long range radar out of Puerto Rico is beginning to show rain echoes from Erika approaching the island.

The forecast for Erika
The computer models have come into better agreement about the track of Erika, taking the storm west-northwest over Puerto Rico and the Dominican Republic. This track will take Erika into a band of significantly higher wind shear of 25 - 35 knots, Friday through Saturday. Considering that Erika is barely maintaining itself as a tropical storm with 20 knots of shear, the combined effects of the higher shear and the encounter with the high mountains of Hispaniola and Puerto Rico should be enough to cause Erika to dissipate by Sunday. Erika's remains will still be capable of dumping very heavy rains of 3 - 5 inches over the Dominican Republic and 1 - 3 inches over Haiti and the Southeast Bahamas, due to the slow motion of the storm. By Monday, when the remains of Erika should be over the Bahamas, the storm will have penetrated through the band of high wind shear over the Greater Antilles, and shear may fall low enough for redevelopment of the storm. This is a scenario offered by the NOGAPS model, which then takes Erika northward towards North Carolina. The other models predict quite a bit more shear in the region than the NOGAPS, and any redevelopment of Erika early next week remains an iffy proposition. The GFDL and HWRF models continue to insist that Erika will brush off the high shear this weekend, avoid Hispaniola, and intensify into a Category 2 hurricane five days from now. These models have not been giving enough emphasis to how the current shear is affecting Erika, and are being discounted at this time.

McAfee virus alert messages
A number of wunderground users with the McAfee virus protection software installed were alerted yesterday that a possible Trojan virus existed on our web pages. After an investigation of the issue, we have determined that this is a false alarm. It appears McAfee updated their virus files yesterday, and included in their list of suspected viruses JavaScript web pages that are compressed using the packer compression system used by wunderground. We've changed the compression technique used on our web pages, and hopefully this will eliminate the bogus McAfee alert messages.

Elsewhere in the Atlantic
A large, strong tropical wave with plenty of spin emerged from the coast of Africa this morning. The wave is not yet generating much in the way of heavy thunderstorms, but has the potential to gradually develop into a tropical depression by early next week. NHC is giving this wave a low (less than 30% chance) of developing into a tropical depression by Saturday. The GFS model has been consistently developing this wave in its runs over the past few days.

I'll have an update this afternoon.

Jeff Masters

Hurricane

Little change to Erika; Jimena makes landfall as a Category 2 hurricane

By: JeffMasters, 7:30 PM GMT on September 02, 2009

Tropical Storm Erika remains weak and disorganized, and the future track and intensity of the storm remain highly uncertain. The center has jumped several times over the past 12 hours, and now lies exposed to view, west of the main area of heavy thunderstorms. Radar animations out of Martinique show little organization of the echoes, and satellite imagery shows no low-level spiral bands or upper-level outflow. Wind shear analyses from the University of Wisconsin diagnose a moderate 10 - 15 knots of shear over Erika, a decrease from yesterday. SSTs are warm, 29°C. The Hurricane Hunters are in the storm now, and have found a slight increase in the surface winds, up to 45 mph. They noted that the surface center was displaced 12 miles north of the center they found at 1500 feet, which is the sign of a disorganized storm undergoing wind shear.

The forecast for Erika
Erika is embedded in a weak steering current pattern, and the storm's current state of disorganization is allowing the center to make random jumps as it reforms near the heaviest thunderstorm activity. This makes for a low-confidence forecast. The future track of the storm will depend upon how strong the storm gets over the next few days. A stronger Erika will extend higher into the atmosphere and be steered more to the northwest by upper-level winds. A weaker Erika will be steered more by the low-level winds, which will keep the storm on a more westerly track. The intensity forecast models did a poor job with Tropical Storm Danny last week, and appear to be repeating that poor performance with Erika. All of the major intensity forecast models predict substantial strengthening of Erika. This seems unlikely to occur, given the storm's current disorganization, and the predicted increase in wind shear along the path of Erika to 20 - 25 knots 3 - 5 days from now. The more southerly than expected track of the storm also brings the possibility that Erika will encounter the high mountains of Puerto Rico and Hispaniola. The GFS, GFDL, and Canadian models predict Erika will pass near Puerto Rico on Friday, then move over Hispaniola on Saturday. Erika in its current weak state would probably not survive an encounter with these islands. A wide range of scenarios is still possible for Erika, from outright dissipation (as forecast by the GFS, Canadian, and ECMWF models) to intensification to a Category 3 hurricane (as forecast by the HWRF model). Erika is a long-term threat to the Bahamas and U.S. East Coast if it is still around five days from now. Potential landfall locations range from Florida on Tuesday to North Carolina on Wednesday. The NOGAPS model has Erika potentially missing the U.S. entirely, scooting northwards between North Carolina and Bermuda. My current expectation is that Erika will dissipate on Saturday when it encounters Hispaniola.


Figure 1. Afternoon image of Tropical Storm Erika. The swirl of clouds just west of Guadeloupe island is the center. This center was what I had labeled a "false center" in this morning's post, and has taken over as the main center this afternoon.

Hurricane Jimena hits Baja
Hurricane Jimena made lanndfall on Mexico's Baja Peninsula late this morning near Cabo San Lazaro as a Category 2 hurricane with 100 mph winds. Jimena is the 2nd strongest hurricane to hit Baja's west coast since record keeping began in 1949. The only stronger storm was Hurricane Norbert, which made landfall in 2008 on the central Baja coast with sustained winds of 105 mph. Jimena has now weakened to a Category 1 storm, and will continue to weaken as it hits colder waters and interacts with land. No deaths or major damage have been reported from the storm.


Figure 2. Hurricane Jimena on Tuesday, Sep. 1, 2009, as seen by NASA's MODIS instrument. Image credit: NASA Earth Observatory.

California fire webcams
As I discussed in yesterday morning's post, you can use our wundermap for Los Angeles with the fire layer turned on to see where the fire and smoke are located, and track the temperatures and winds during today's air pollution event. We also have two webcams with views of the fire: Altadena and Tujunga.

I'll have an update Thursday morning.

Jeff Masters

Hurricane

Tropical Storm Erika's future highly uncertain

By: JeffMasters, 2:21 PM GMT on September 02, 2009

The tropical wave we were calling Invest 94 finally decided to stop dawdling and become Tropical Storm Erika yesterday. However, Erika seems intent upon keeping us guessing about its intentions, as the storm's future track and intensity remain highly uncertain. After a modest burst of intensification to a 60 mph tropical storm last night, Erika has become quite disorganized this morning. The Hurricane Hunters found multiple swirling centers inside Erika early this morning, and the main center took a jump to the southwest to relocate itself under a batch of intense thunderstorms. The exact location and path of Erika remain uncertain at this point, and it is possible the storm will have another center relocation later today. Wind shear analyses from the University of Wisconsin diagnose a moderate 10 - 15 knots of shear over Erika, a decrease from yesterday. SSTs are warm, 29°C. Why, then, is Erika so disorganized? The trouble with the various wind shear analyses we use is that they take a crude average of winds over a thick layer to arrive at an average shear, and this large-scale average shear does not capture thin layers of shear that can dramatically affect a tropical cyclone. Upper air data from Guadeloupe and Saint Martin from last night show a complicated shear pattern in Erika's region, with 30 knot winds out of the south to southwest at 200 mb height, nearly calm winds between 300 - 500 mb, and northeasterly winds of 10 - 20 knots from the surface to 500 mb. Some extremely dry air with humidities near 10% was present in a thin layer near 600 mb on the Guadeloupe sounding, so dry air from the Saharan Air Layer is probably being injected by a northeasterly jet of wind into the core of Erika. The shear of 30 knots at the top of the storm is ripping away the heat and moisture Erika's thunderstorms are lifting there, and the result of the shear and dry air is a very disorganized tropical storm.

Erika is embedded in a weak steering current pattern, and the future track of the storm will depend greatly upon how strong the storm gets over the next few days. A stronger Erika will extend higher into the atmosphere and be steered more to the northwest by upper-level winds. A weaker Erika will be steered more by the low-level winds, which will keep the storm on a more westerly track. Given the complicated nature of the wind shear pattern in the region, it is difficult to forecast how strong Erika will get. Virtually anything can happen over the next five days, from dissipation (as forecast by the ECMWF model) to intensification to a Category 3 hurricane (as forecast by the HWRF model). Large-scale wind shear is expected to increase to 20 - 25 knots between 3 - 4 days from now, so Erika will have to deal with an increasing amount of adversity. The storm is a long-term threat to the Bahamas and U.S. East Coast, particularly if the storm stays weak over the next three days. Potential landfall solutions from the models range from Florida on Tuesday (GFS model) to North Carolina on Wednesday (Canadian model).


Figure 1. Morning image of Tropical Storm Erika, showing a false center over Guadaloupe--one of several surface swirls the Hurricane Hunters found in the storm.

Elsewhere in the tropics
The tropical wave off the coast of Africa we were watching on NHC's Tropical Weather Outlook as having a low chance of developing into a tropical depression has been done in by the dry air of the Sahara, and is no longer a threat to develop. A large and well-organized tropical wave will emerge from the coast of Africa on Thursday, and several of the models develop this low into a tropical depression by early next week. The remains of an old cold front off the coast of North Carolina could serve as a breeding ground for some tropical development Friday or Saturday, but anything that forms in this region would get swept quickly northeastward into New England by Sunday without enough time to become a tropical depression.

Hurricane Jimena nears Baja
Hurricane Jimena has steadily weakened over the past day, and is now down to a Category 2 hurricane with 105 mph winds. The storm should continue to steadily weaken over the next 24 hours as the waters under the hurricane cool from 28°C to 27°C. Jimena is battering a relatively unpopulated stretch of coast, and largely spared the tourist mecca on the southern tip of Baja. It now appears unlikely that moisture from Jimena will reach the Southwestern U.S., and the hurricane appears poised to stall out over Baja and die five days from now.


Figure 2. Hurricane Jimena on Tuesday, Sep. 1, 2009, as seen by NASA's MODIS instrument. Image credit: NASA Earth Observatory.

Baja's hurricane history
The most powerful hurricane on record to hit the west coast of Baja occurred last year, when Hurricane Norbert made landfall on the central Baja coast with sustained winds of 105 mph (Category 2) . Norbert's central pressure of 956 mb at landfall made it the 3rd strongest hurricane to hit the Pacific coast of Mexico since record keeping began in 1949. Norbert killed eight, knocked out power to 20,000 homes, and damaged or destroyed 40% of the homes on the islands of Margarita and Magdalena. Norbert crossed the Baja Peninsula and made landfall on Mainland Mexico as a Category 1 hurricane with 85 mph winds.

Only two major hurricanes have made landfall on Baja since record keeping began in 1949. Both hurricanes hit the east (Gulf of California) side of Baja. The first was Hurricane Olivia of 1967. Olivia made landfall on October 13, 1967 as a Category 3 hurricane with 125 mph winds. Due to its small size and the unpopulated region of coast it hit, damage was minimal. The second major hurricane was Hurricane Kiko, which made landfall on August 27, 1989, as a Category 3 hurricane with winds of 115 mph (minimal Category 3). Kiko was a small hurricane and hit a relatively unpopulated area, resulting in no loss of life and only scattered reports of damage.


Figure 3. A plot of all the major hurricanes to pass within 200 miles of Mexico's Baja Peninsula since 1949. Image credit: NOAA Coastal Services Center.

California fire webcams
As I discussed in yesterday morning's post, you can use our wundermap for Los Angeles with the fire layer turned on to see where the fire and smoke are located, and track the temperatures and winds during today's air pollution event. We also have two webcams with views of the fire: Altadena and Tujunga.

I'll have an update by 4pm this afternoon, when the data from the next hurricane hunter flight into Erika will be available.

Jeff Masters

Hurricane

Tropical Storm Erika likely soon; a weaker Jimena powers towards Baja

By: JeffMasters, 7:48 PM GMT on September 01, 2009

Hurricane Jimena has weakened to a low-end Category 4 hurricane with 135 mph winds, thanks to the collapse of its inner eyewall. The hurricane is undergoing a process common in intense hurricanes called an Eyewall Replacement Cycle (ERC), where the eye shrinks to a size too small to be stable, resulting in the disintegration of the eyewall, and the formation of a new eyewall from one of the outer spiral bands. Once the new eyewall becomes stable tonight, Jimena has an opportunity to re-strengthen.

The latest set of 12Z model runs show little change in Jimena's track. The hurricane is still expected to make landfall Wednesday along Mexico's Baja Peninsula. If the hurricane makes landfall over the southern portion of Baja, it would likely be at major hurricane strength. However, SSTs cool quickly to 23°C at the middle of the Baja Peninsula, and Jimena would likely weaken to a Category 2 or 1 hurricane if it makes a strike towards the middle of Baja. The computer models are split on what might happen once Jimena makes landfall on Baja, with one camp predicting a northeast turn bringing the storm over Mainland Mexico and eventually into Arizona, and the other camp stalling Jimena out over or just west of Baja. Regardless, the main threat from Jimena will be flooding and mudslides due to heavy rains.

Baja's hurricane history
The most powerful hurricane on record to hit the west coast of Baja occurred last year, when Hurricane Norbert made landfall on the central Baja coast with sustained winds of 105 mph (Category 2) . Norbert's central pressure of 956 mb at landfall made it the 3rd strongest hurricane to hit the Pacific coast of Mexico since record keeping began in 1949. Norbert killed eight, knocked out power to 20,000 homes, and damaged or destroyed 40% of the homes on the islands of Margarita and Magdalena. Norbert crossed the Baja Peninsula and made landfall on Mainland Mexico as a Category 1 hurricane with 85 mph winds.

Only two major hurricanes have made landfall on Baja since record keeping began in 1949. Both hurricanes hit the east (Gulf of California) side of Baja. The first was Hurricane Olivia of 1967. Olivia made landfall on October 13, 1967 as a Category 3 hurricane with 125 mph winds. Due to its small size and the unpopulated region of coast it hit, damage was minimal. The second major hurricane was Hurricane Kiko, which made landfall on August 27, 1989, as a Category 3 hurricane with winds of 115 mph (minimal Category 3). Kiko was a small hurricane and hit a relatively unpopulated area, resulting in no loss of life and only scattered reports of damage.


Figure 1. A plot of all the major hurricanes to pass within 200 miles of Mexico's Baja Peninsula since 1949. Image credit: NOAA Coastal Services Center.

Invest 94L almost Tropical Storm Erika
The Air Force Hurricane Hunters are investigating tropical wave 94L, about 200 miles east of the Lesser Antilles Islands. So far this afternoon, they have found a broad circulation with top winds of 45 - 50 mph in heavy thunderstorms on the east side. The circulation may be too broad for 94L to be considered a tropical storm, but visible satellite imagery shows that the circulation is getting better defined, and 94L's heavy thunderstorms are moving closer to the center of circulation. Recent satellite wind shear analyses by NOAA/Colorado State University and the University of Wisconsin show that wind shear is a moderate 10 - 20 knots over 94L, and this shear is keeping any thunderstorms from developing on the system's west side.

The forecast for 94L
The latest of 12Z model runs are more in tune with the idea that 94L will become a tropical storm, with the latest ECMWF run now on board. The storm will be steered west-northwest to northwest over the next three days thanks to the presence to two upper-level lows to the northwest of the storm. Since most of 94L's heavy thunderstorms and high winds are on the east side, the northern Lesser Antilles and Puerto Rico will probably be spared tropical storm force winds from this system. The best guess track for 94L, assuming it does intensify into a tropical storm in the next 24 hours, is on a northwest path between the Bahamas and Bermuda. If 94L stays weak, a more southerly path, along the northern edge of the Bahama Islands, is more likely.


Figure 2. Infrared satellite image taken at 12pm EDT, Tuesday Sep 1, 2009. Five major African tropical waves are apparent. Image credit: Navy Research Lab, Monterey.

Elsewhere in the tropics
It's September, the most active month for hurricane activity in the Northern Hemisphere. There's every indication that the 2009 Atlantic hurricane season will have an active first half of September, since SSTs are 0.5 - 1.0°C above average, wind shear is near average, and the African monsoon is sending a long parade of African waves spinning off the coast of Africa. An IR satellite image from noon today shows this activity well (Figure 2). We can see a line-up of five African waves stretching from the Lesser Antilles to eastern Africa. The GFS model develops the waves numbered "2" and "3" into tropical depressions next week, and the waves labeled "1" and "4" also have a chance to develop into tropical depressions, as well. The wave labeled "1" is mentioned on NHC's Tropical Weather Outlook as having a low (less than 30%) chance of developing into a tropical depression by Thursday. This wave is under a moderate 10 - 15 knots of wind shear, and is over sufficiently warm waters (27 - 28°C) that some development may occur this week. The wave is far enough north that it will be hampered by dry air from the Sahara Desert.

California fire webcams
As I discussed in this morning's post, you can use our wundermap for Los Angeles with the fire layer turned on to see where the fire and smoke are located, and track the temperatures and winds during today's air pollution event. We also have two webcams with views of the fire: Altadena and Tujunga.

Jeff Masters

Hurricane

Hurricane Jimena, California smoke, and Invest 94L

By: JeffMasters, 2:10 PM GMT on September 01, 2009

The most powerful hurricane on the planet so far this year, Hurricane Jimena, continues to maintain an intensity just below Category 5 strength. Jimena's 155 mph winds beat out the South Pacific's Tropical Cyclone Hamish (150 mph winds) as the most powerful tropical cyclone so far this year. Satellite estimates of Jimena's strength continue to show no weakening of the hurricane, and the Hurricane Hunters are currently enroute to Jimena to see exactly how strong the hurricane is.

Jimena is expected to make landfall Wednesday along the Mexico's Baja Peninsula. The hurricane is in an environment with low wind shear, 5 - 10 knots, and warm Sea Surface Temperatures (SSTs), 29°C. Shear is expected to remain low, and SSTs will decline to 28°C with a decrease in total oceanic heat content between now and landfall, and these conditions should allow Jimena to be a Category 3 or 4 hurricane at landfall. The computer models remain in good agreement that Jimena will miss the southern Baja resort town of Cabo San Lucas, and make landfall midway up the Baja Peninsula. However, just a small deviation in track would bring Jimena ashore in southern Baja. Cabo San Lucas has a 13% chance of receiving hurricane force winds, according to NHC's wind probability product. Serious flooding due to heavy rains will occur across all of the southern Baja today and Wednesday. Jimena is of similar intensity and is following a similar track to Hurricane Juliette of 2001, which brought 17.7" of rain to Cabo San Lucas. Juliette weakened to a 45 mph tropical storm before hitting Baja, but the storm killed 7 people and caused $20 million in damage to Mexico, mostly due to flash flooding and mudslides from the heavy rains. Jimena will probably be one of the strongest hurricanes ever to hit Baja.

After Jimena makes initial landfall on Baja, it will cross over the Gulf of California and make landfall on Mainland Mexico. Depending upon how up along the coast this second landfall occurs, Arizona may receive moisture from Jimena late this week that will be capable of causing flooding rains.


Figure 1. Rainfall totals from Hurricane Juliette of 2001, which had a similar track and intensity as Hurricane Jimena. Image credit: NOAA.

California fires creating major air pollution event
The wildfires burning east of Los Angeles, California have created a major air pollution event, and will continue to impact air quality for millions of people in Southern California today. The fires have burned over 90,000 acres and have led to Unhealthy to Hazardous Air Quality Index (AQI) levels (Code Red to Code Brown) for the past five days in nearby regions. Not only are fine smoke particles directly elevating the most deadly form of air pollution--particle pollution, the gases in the smoke are reacting with sunlight to form ground-level ozone, another dangerous pollutant. High pressure over the southwestern states today will keep temperatures hot and relative humidity low in the vicinity of the fires. Smoke has settled into the valleys of Los Angeles County overnight and in the eastern San Bernardino Valley. While onshore ocean breezes Tuesday afternoon are expected to move smoke into the mountains, winds will also increase fire growth potential. Air pollution levels will continue to reach the Unhealthy level (code red, see Figure 2) today over much of the Los Angeles area. By Wednesday, weather conditions will improve as the high pressure region over Southern California weakens and moves east, bringing cooler temperatures, higher humidity, and stronger airflow from the cool ocean, aiding firefighting efforts.

Health tip: People in areas directly impacted by smoke should avoid any vigorous exertion, indoors or outdoors. In addition, people with respiratory or heart disease, the elderly, and children should remain indoors. Individuals without air conditioning who stay inside with the windows closed may be in danger during extremely hot weather. In these cases, individuals should seek alternative shelter. For the latest information on this air pollution event, see the latest South Coast Air Quality Management District Air Quality Advisory.

Check out our wundermap for Los Angeles with the fire layer turned on to see where the fire and smoke are located, and track the temperatures and winds during today's air pollution event.


Figure 2. NASA MODIS satellite image of the California fires of August 31, 2009 (top) with air pollution levels at major cities superimposed. Bottom: air quality forecast for today, September 1, 2009. Image credit: EPA AIRNOW.

Invest 94L strong but disorganized
Tropical wave 94L, about 250 miles east of the Lesser Antilles Islands, continues to toy with the idea of becoming a tropical depression. Infrared satellite imagery shows the low has developed a region of heavy thunderstorms that extend high into the atmosphere. This morning's QuikSCAT pass showed surface winds of 45 mph beneath these thunderstorms. However, QuikSCAT showed no surface circulation, with a large and rather confused region of wind shifts and lines of convergence at the surface. Recent satellite wind shear analyses by NOAA/Colorado State University and the University of Wisconsin show that wind shear has oscillated between 10 - 20 knots over 94L this morning, and this shear is keeping the storm disorganized. Also, last night's upper-air balloon sounding from Guadeloupe is showing the presence of a narrow jet of 30 knot winds from the east at 700 mb (3000 meters). The relatively crude measures of shear we use, taking the difference between the wind at 200 mb and 850 mb, will miss seeing these sort of this layers of shearing winds that can have a strong negative impact on the organization of a developing tropical disturbance. It is apparent from visible satellite imagery that shear is causing some disruption to the southwest side of 94L, and that there is no surface circulation. The storm also has fewer low-level spiral bands than yesterday.

The forecast for 94L
The latest of 00Z and 06Z model runs continue to be split on whether 94L will develop or not, with the GFDL and HWRF models bringing 94L to hurricane strength in 4 days, and the NOGAPS and ECMWF predicting 94L will just be a disturbance 4 days from now. SSTs will be warm, in the 28 - 29°C range, and dry air should have only a minor inhibiting effect, but high shear may continue to delay 94L from developing into a tropical depression for several days. The storm is moving more slowly today, about 10 mph, and will be steered west-northwest to northwest over the next three days thanks to the presence to two upper-level lows to the northwest of the storm. The degree of northward motion of 94L will depend upon how soon the storm becomes a tropical depression and begins intensification. If 94L follows the GFDL and HWRF model's predictions, and intensifies into a hurricane four days from now, a more northwestward track taking the storm between the Lesser Antilles and Bermuda is likely. If 94L lingers a few more days as a tropical disturbance, a more southerly track over the northern Lesser Antilles Islands, Puerto Rico, and the Bahamas is more likely.

The Hurricane Hunters will investigate 94L at 2 pm this afternoon, and I'll update the blog by 3:30 pm.

Jeff Masters

Fire Hurricane


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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About

Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather