Category 6™

Disturbance 95L over Florida weakens

By: JeffMasters, 11:18 AM GMT on June 30, 2007

Clouds and showers associated with a weak low pressure system (dubbed 95L by NHC) over South Florida have become very disorganized. Wind shear has increased to a high 25-30 knots. This high wind shear, combined with the fact that the storm's center is over land gives it no chance for development today.

Long range radar from Melbourne, Florida shows little activity over Florida this morning, but this will change during the afternoon when the afternoon sea breezes get going and help create the lift needed to trigger thunderstorms. Heavy rains of one to four inches were common across South Florida and the northwestern Bahama Islands Friday. Lesser amounts are likely today.

A trough of low pressure is scheduled to push off the U.S. Southeast Coast on Monday, and will probably sweep 95L out to sea in front of it. There is a chance 95L could develop on Monday as it moves to the northeast away from land, in front of the trough. Wind shear is forecast to drop on Monday to about 10-20 knots in this region, which is low enough to allow for some tropical development. However, none of the reliable computer models are forecasting tropical storm formation anywhere in the Atlantic over the coming week.


Figure 1. Preliminary model tracks for the disturbance over Florida.

One other area to watch is the region just north of Panama in the Southwest Caribbean. Wind shear values have dropped to 10 knots there this morning, and are forecast to remain low for several days.

Jeff Masters

Disturbance 95L over South Florida bringing heavy rains

By: JeffMasters, 1:27 PM GMT on June 29, 2007

Clouds and showers associated with a weak low pressure system over South Florida have increased markedly this morning. NHC has designated this system "95L". Long range radar from Melbourne, Florida shows an expanding area of echoes, but there are no signs of any organization or spin. With wind shear remaining high at 20-30 knots, I'm not expecting any development of this disturbance today. Some of the computer models are forecasting that wind shear will slowly drop the next three days, so we'll have to keep a closer eye on 95L over the weekend. The system could bring heavy rains to South Florida and the northwestern Bahama Islands the next two or three days. A Hurricane Hunter airplane is on call to investigate the system Sunday at 2pm, if necessary.

A trough of low pressure is scheduled to push off the U.S. Southeast Coast on Monday, and will probably sweep 95L out to sea in front of it. There is a chance something could develop along the remains of a cold front the trough leaves behind over the Gulf Stream. However, none of the reliable computer models are forecasting any tropical storm formation over the coming week.


Figure 1. Preliminary model tracks for the disturbance near South Florida.

One other area to watch is the region just north of Panama in the Southwest Caribbean. Wind shear values are forecast to drop below 5 knots there by Sunday.

Wind shear decline expected
The jet stream usually divides itself into two branches this time of year--a strong jet whose average position is near the U.S.-Canadian border (the polar jet), and a weaker branch whose average position is over the Gulf of Mexico (the subtropical jet). Both of these branches of the jet stream bring high upper level winds (and thus high wind shear) over the Atlantic Ocean. All of the computer models are forecasting that the subtropical jet will weaken substantially over the next ten days, bringing much lower than average wind shear to the tropical Atlantic. It is normal to see the subtropical jet weaken in the summer, but it usually happens a month later than this--in August. The expected early weakening of the subtropical jet should give us an above-average risk of a July tropical storm. I'll have a full analysis of the possibilities on Monday, when I post my bi-monthly 2-week outlook.

Jeff Masters

India's shocking failure to provide hurricane warnings for Pakistan

By: JeffMasters, 12:44 PM GMT on June 28, 2007

A very serious failure occurred on the part of India's Meteorological Department (IMD) yesterday, when they failed to provide adequate warnings for a devastating tropical cyclone that hit Pakistan. Cyclone 03B, which struck the coast of Pakistan at 02 GMT June 27, has killed at least 17 and left 250,000 homeless in that nation, according to early news reports. Under mandate from the World Meteorological Organization (WMO), India is responsible for warning the shores of all nations along the North Indian Ocean, including Pakistan. Cyclone 03B was at least a strong tropical storm when it hit Pakistan, and was probably a Category 1 hurricane. Microwave satellite imagery near the time of landfall (Figure 1) shows a well-developed tropical cyclone with spiral banding and a cloud free eye. Yet IMD never even gave the storm a name, and merely classified it as a a "deep depression," with winds less than tropical storm force (39 mph). At 00 GMT June 26, two hours before landfall, the position of Cyclone 03B given by IMD was probably in error by at least 60 miles. One hour later, at 01 GMT, with landfall just one hour away, the IMD shipping advisory said that landfall was still 12 hours away. The IMD website, with the warnings, was offline and not available for approximately twelve hours beginning with the landfall period. It's important not to judge IMD before all the facts are known, but I can't fathom any excuse that can account for what appears, at best, to be criminal incompetence. I hope the WMO fully investigates this complete failure of India's Meteorological Department to protect the lives and welfare of those living along the Pakistani coast. Much more information on this dismaying story is presented in today's View From the Surface blog, which I have used to construct this short summary.


Figure 1. Microwave satellite image of Cyclone 03B at 0113 GMT June 26, 2007, about one hour before landfall. Note the cloud free eye and well-developed spiral banding, indicative of a strong tropical storm or weak Category 1 hurricane.

Atlantic tropical update
Clouds and showers associated with a westward-moving tropical wave over the Bahamas, near the east coast of Florida, show no signs of organization. With wind shear at 20-30 knots, I'm not expecting any development of this disturbance. The next best chance of development in the Atlantic may be Monday, when a cold front will push off the U.S. East Coast. We'll have to watch the area between Florida and North Carolina when the remains of the front stall out over the Gulf Stream. Also, the area just north of Panama in the Southwest Caribbean needs to be watched beginning Saturday, when wind shear values are forecast to drop below 5 knots.

Jeff Masters

An American Tragedy: 50th Anniversary of Hurricane Audrey

By: JeffMasters, 11:39 AM GMT on June 26, 2007

Fifty years ago this evening--on the night of June 26, 1957--residents of Cameron, Louisiana slept uneasily. Cameron, population 3,000, sat on the coast just above sea level, about 30 miles east of Texas. Hurricane Audrey roared across the dark waters of the Gulf of Mexico towards Cameron that night, lashing the coast with high winds and heavy rain. Many residents had heeded calls to evacuate from Audrey's 100 mph winds and predicted 5-9 foot storm surge that afternoon. But the old timers, familiar with how the surrounding dunes had protected Cameron in the past, stayed put. It was, after all, June, and severe hurricanes in June were almost unheard of. Besides, the storm was not expected to hit until the following afternoon, so there was still time to evacuate in the morning if things looked bad. The remarkable mass exodus of thousands of crawfish from the marshes surrounding Cameron that night apparently did not concern the old timers, who figured they had more sense than crawdads. But the crawdads could apparently sense what the old timers could not--sea surface temperatures were a full 2-3 degrees Fahrenheit above average in the Gulf of Mexico, with a large upper level anticyclone bringing near-zero wind shear over Audrey. This perfect recipe for rapid intensification meant that Audrey was not going to be a mere Category 2 hurricane at landfall. An additional ingredient unfavorable for intensification--the approach of a trough of low pressure with increased wind shear--would not occur in time to weaken the storm. However, the approaching trough did bring an increase in steering current winds at mid- and high levels of the atmosphere, which doubled the forward speed of Audrey overnight.


Figure 1. Radar image of Hurricane Audrey on June 27, 1957, a few hours before landfall. Image credit: US Air Force/NOAA.

Not everyone got the warning a hurricane was coming, since Cameron was isolated and didn't get good radio reception. Television sets were still too new to be commonplace. Those Cameron residents who were able to get the warnings saw this before they went to bed June 26:

NEW ORLEANS WEATHER BUREAU
HURRICANE WARNING AND ADVISORY NUMBER 7 AUDREY
10 PM CST JUNE 26 1957

CHANGE TO HURRICANE WARNINGS 10 PM CST O UPPER TEXAS COAST AS FAR SOUTH AS HIGH ISLAND. LOWER STORM WARNINGS EAST OF LOUISIANA TO PENSACOLA>

AT 10 PM CST...0400Z...HURRICANE AUDREY WAS CENTERED ABOUT 235 MILES SOUTH OF LAKE CHARLES LOUISIANA NEAR LATITUDE 27.0 LONGITUDE 93.5 MOVING NORTHWARD ABOUT 10 MPH. THIS MOVEMENT IS EXPECTED TO CONTINUE AND THE AREA FROM HIGH ISLAND TO MORGAN CITY IS EXPECTED TO BEAR THE BRUNT OF THIS HURRICANE THURSDAY.

HIGHEST WINDS ARE ESTIMATED 100 MPH NEAR CENTER AND GALES EXTEND OUT 150 TO 200 MILES TO EAST AND NORTH OF CENTER AND 50 MILES TO THE SOUTHWEST.

TIDES ARE EXPECTED TO REACH 5 TO 9 FEET FROM HIGH ISLAND TEXAS TO MORGAN CITY LOUISIANA AND 3 TO 6 FEET ELSEWHERE FROM FREEPORT TEXAS TO BILOXI MISSISSIPPI BY LATE THURSDAY. ALL PERSONS IN LOW EXPOSED PLACES SHOULD MOVE TO HIGHER GROUND. WINDS ARE INCREASING ALONG THE UPPER TEXAS AND LOUISIANA COASTS AND WILL REACH GALE FORCE TONIGHT AND EARLY THURSDAY.

HURRICANE WARNINGS ARE DISPLAYED ALONG THE ENTIRE LOUISIANA COAST AND ON THE UPPER TEXAS COAST AS FAR SOUTH AS HIGH ISLAND AND STORM WARNINGS AT GALVESTON. THE THREAT OF HURRICANE FORCE WINDS OVER SOUTHEAST LOUISIANA HAS LESSENED CONSIDERABLY.

NEXT ADVISORY AT 4 AM CST BULLETIN AT 1 AM CST.

CONNER WEATHER BUREAU NEW ORLEANS

Overnight, Audrey intensified rapidly, and more than doubled her forward speed from the 7 mph speed observed that afternoon. When residents of Cameron awoke on June 27, the escape routes had already been flooded by the storm surge. Audrey now packed top winds of 145-150 mph--an extremely dangerous Category 4 hurricane, the most powerful June hurricane on record. A massive storm surge of 12 feet swept through the bayous the morning of June 27, pushing inland over 25 miles. The final death toll will never be known, but it is thought 550 people--including over 100 children--perished in Audrey. It was America's deadliest hurricane disaster between the time of the New England Hurricane of 1938 (682 killed) and Hurricane Katrina of 2005 (1833 killed).

Comparison of Audrey and Rita
Why was Audrey so much deadlier than Hurricane Rita of 2005? Rita hit the same region of coast with weaker winds (Category 3, 115 mph), but a storm surge even higher (15 feet). Rita destroyed virtually 100% of Cameron, whereas Audrey destroyed 75% of the town. Nearly two years later, Cameron is mostly just concrete slabs and trailers, thanks to Rita. However, Rita caused only one direct death in Southwest Louisiana--a drowning in Lake Charles. The answer is preparedness. Rita was a massive Category 5 hurricane several days before landfall, giving people plenty of time to receive the warnings and evacuate. Warning systems are much better now than in 1957, and Cameron was deserted when Rita hit. But Audrey did something hurricane forecasters still fear could cause a high death toll in the future, despite our better warning systems--rapid intensification with a sudden forward speed increase overnight, bringing a much stronger hurricane to the coast far earlier than expected. If this nightmare scenario happens to one of our major cities in the future, another Audrey-like death toll could easily result.


Figure 2. Comparison of wind gusts from Audrey (1957) and Hurricane Rita (2005), which both hit the same region of coast. Image credit: NOAA.

Other Audrey links
The National Weather Service Lake Charles Office's 50th anniversary of Hurricane Audrey web page. They've got a nice SLOSH model animation of the storm surge, plus radar images and meteorological data.

The NOAA history web site has the story, "My Battle with Audrey", a graphic first-hand description of an Audrey survivor.

Nola Mae Ross has written a book about Hurricane Audrey. Here's the web site to buy the book from.

Wikipedia.

Remembering Audrey by Ron Thibodeaux, writer for the Times-Picayune newspaper.

Louisiana101.com has photos of the memorial at the mass grave where hundreds of Audrey's victims are buried. I found this memorable poem by student Lucas Lasha on the website:

In '57 she began with a roar
No one knew she was comin' ashore
Most people were asleep in bed
Not knowing they should have fled.

After the fury of the storm's huge eye
Families cried for members who did die
Lady Audrey would long be remembered
As the fateful day that Cameron surrendered

Jeff Masters

Fourth warmest May on record

By: JeffMasters, 12:25 PM GMT on June 25, 2007

The tropical Atlantic remains quiet. None of the computer models are showing any tropical development over the next week. The best chance of a new threat area to watch may not occur until July 1, when a strong cold front pushes off the U.S. East Coast.

The Middle East will see their second tropical cyclone of the month on Tuesday. Tropical Cyclone 3B crossed India, killing at least 140, and re-formed in the Arabian Sea, and is poised to hit Iran or Pakistan tomorrow. The View From the Surface blog is following this storm. We may looking at hundreds of years since the last time the Middle East was hit by two tropical cyclones in the same month. Tropical Cyclone Gonu pounded Oman and Iran earlier this month.

Fourth Warmest May on record
May 2007 was the fourth warmest May for the globe on record, and the period January - May of 2007 was tied with 1998 for the warmest such period ever, according to statistics released by the National Climatic Data Center. The global average temperature for May was +0.53�C (+0.95�F) above the 20th century mean. Over land, May global temperatures were the warmest ever measured, the second straight month that has happened. Ocean temperatures were a bit cooler (ninth warmest on record), thanks to the cooling associated with the disappearance of the winter El Ni�o event. The global temperature record goes back 128 years.

May temperatures were particularly warm across Russia. Moscow recorded its highest May temperature since record keeping began 128 years ago--32.9�C (91.2�F). The heat forced Russia's energy administrator to restrict the use of non-residential energy for the first time in summer. In India, a heat wave during mid-May produced temperatures as high as 45-50�C (113-122�F) resulting in at least 128 fatalities. Dr. Ricky Rood's Climate Change blog has more on the India heat wave. Although record heat was more prevalent across the globe, Argentina experienced its coldest May in twenty years, and at least 23 fatalities were reported as a result of cold weather during the last week of May.

11th warmest May on record in the U.S.
In the U.S., May 2007 ranked as the 11th warmest since record keeping began in 1895. The period January through May was the 20th warmest such period on record. Spring (March - May) was 5th warmest on record in the continental U.S. The past six months (Dec-May) were the driest on record for the Southeast U.S. Portions of Alabama, Mississippi, and Tennessee are experiencing exceptional drought. However, the drought has eased some since late May over the Florida Peninsula.


Figure 1. Temperature departure from average for May 2007. Image credit: National Climatic Data Center.

Sea ice extent
Sea ice extent in the Arctic for May was the third lowest on record, a modest recovery from the lowest ever sea ice coverage observed in April. Arctic sea ice coverage in May has declined by about 8% since measurements began in 1979 (Figure 2).


Figure 2. Arctic sea ice extent for May, for the years 1979-2007. May 2007 had the third lowest Arctic sea ice extent since satellite measurements began in 1979. May sea ice coverage has declined about 8% since 1979. Image credit: National Snow and Ice Data Center.

I'll have a new blog on Tuesday.
Jeff Masters

Climate Summaries

Quiet tropics; update on Bill Proenza's doings

By: JeffMasters, 2:43 PM GMT on June 22, 2007

The tropical Atlantic is quiet today. The low pressure system over northern Florida that brought rain to the state Thursday has moved out to sea and weakened. Wind shear is high over this low, sea surface temperatures beneath it are cool, and I don't expect any development. None of the computer models are showing any tropical development over the next week. Our best chance of a new threat area to watch may not occur until the next strong cold front pushes off the U.S. East Coast. The long range GFS model forecast expects this to happen around Saturday June 30.

Bill Proenza news
In the absence of much to talk about in the tropics, we can always talk about the latest on new NHC director Bill Proenza. The View from the Surface blog is keeping up with the latest. Last night, I listened in to Proenza's comments on the Barometer Bob Show, an Internet radio show. I asked him where he got his numbers of 16% and 10% improvement for 72-hour and 49-hour hurricane track forecasts made using QuikSCAT satellite data (his boss, acting NWS director Mary Glackin, said "I'm not willing to stand by those numbers.") Proenza cited a study done of hurricane tracks from 2003 that showed these improvements, and Margie Kieper is working on getting a copy of this study for the View From the Surface blog. Margie came across a 2006 study which shows that for one storm studied (Hurricane Cindy of 1999), inclusion of QuikSCAT data improved track forecasts at 24 hours and 48 hours by 30-50% (Figure 1). There is also a 2007 study which showed improvements of 25%-50% for 24 hour - 48 hour model track forecasts of 2002's Hurricane Isidore using QuikSCAT data vs. no QuikSCAT data (Figure 2). We'll have more on the ongoing Bill Proenza hullaballo next week, with more info on just how important QuikSCAT is to hurricane forecasting.


Figure 1. Forecast error in the track of Hurricane Cindy (1999) with and without using QuikSCAT data. Image credit: NOAA. Data taken from the 2006 paper, The use of remotely sensed data and innovative modeling to improve hurricane prediction, by Robert Atlas, O. Reale, B-W. Shen, and S-J. Lin.


Figure 2. Forecast error in the track of Hurricane Isidore (2002) with and without using QuikSCAT data. Image credit: American Meteorological Society, "The Impact of Assimilating SSM/I and QuikSCAT Satellite Winds on Hurricane Isidore Simulations", by Shu-Hua Chen. Monthly Weather Review 135, issue 2, pp 549-566, February 2007.

Jeff Masters

Politics

Less active Atlantic hurricane season foreseen by new model

By: JeffMasters, 1:33 PM GMT on June 20, 2007

A major new player in the seasonal Atlantic hurricane season forecast game is here--the UK Met Office, which issued its first Atlantic hurricane season forecast yesterday. The UK Met Office is the United Kingdom's version of our National Weather Service. Their 2007 Atlantic hurricane season forecast calls for ten named storms for the remainder of the season--12 for the entire season, when one includes Andrea and Barry. They make no forecasts for number of hurricanes or intense hurricanes, nor where the storms may strike. The UK Met Office forecast of ten storms for July through November is below the average of 12.4 for the active hurricane period that began in 1995, and well below the predictions of the other major seasonal forecast teams.

July-November 2007 Atlantic hurricane season forecasts (adjusted for the occurrence of Tropical Storms Andrea and Barry, where appropriate):

UK Met Office (June 19): 10 named storms.

Colorado State University (CSU) Phil Klotzbach/Dr. Bill Gray forecast (May 31): 16 named storms.

NOAA's forecast (May 22): 11-15 named storms.

Tropical Storm Risk, Inc. (TSR) forecast (June 4): 14.7 named storms.

How reliable are the UK Met Office forecasts?
This is the first year that the UK Met Office has issued a forecast of hurricane season activity, so we don't have any previous years to evaluate their forecasts. The results of their experimental forecasts issued for the 1987-2002 seasons are scheduled to be published later this year in the peer-reviewed journal Geophysical Research Letters. The UK Met Office claims that their forecast out-performed the forecasts made for the 2005 and 2006 Atlantic hurricane season issued by the other major seasonal forecast groups. I have high hopes for the UK Met Office forecast, since it is based on a promising new method--running a dynamical seasonal prediction computer model of the global atmosphere-ocean system. The Dr. Bill Gray/CSU forecast is based on statistical patterns of hurricane activity observed from past years. These statistical techniques do not work very well when the atmosphere behaves in ways it has not behaved in the past. The UK Met Office forecast avoids this problem by using a global computer forecast model--the GloSea model (short for GLObal SEAsonal model). GloSea is based on the HadCM3 model--one of the leading climate models used to formulate the influential UN Intergovernmental Panel on Climate Change (IPCC) report. GloSea subdivides the atmosphere into a 3-dimensional grid 3.75° in longitude, 2.5° in latitude (277.5 km), and 19 levels in the vertical. This atmospheric model is coupled to an ocean model of even higher resolution. The initial state of the atmosphere and ocean as of June 1, 2007 were fed into the model, and the mathematical equations governing the motions of the atmosphere and ocean were solved at each grid point every few minutes, progressing out in time until the end of November (yes, this takes a colossal amount of computer power!) It's well-known that slight errors in specifying the initial state of the atmosphere can cause large errors in the forecast. This "sensitivity to initial conditions" is taken into account by making many model runs, each with a slight variation in the starting conditions which reflect the uncertainty in the initial state. This generates an "ensemble" of forecasts and the final forecast is created by analyzing all the member forecasts of this ensemble. Forty ensemble members were generated for this year's UK Met Office forecast. The researchers counted how many tropical storms formed during the six months the model ran to arrive at their forecast of ten named storms for the remainder of this hurricane season. Of course, the exact timing and location of these ten storms are bound to differ from what the model predicts, since one cannot make accurate forecasts of this nature so far in advance.

The grid used by GloSea is fine enough to see hurricanes form, but is too coarse to properly handle important features of these storms. This lack of resolution results in the model not generating the right number of storms. This discrepancy is corrected by looking back at time for the years 1987-2002, and coming up with correction factors (i.e., "fudge" factors) that give a reasonable forecast. This year's GloSea forecast shows a cooling trend in the tropical Atlantic sea surface temperature (SST) compared to what we've seen in recent years, and is a major reason why the UK Met Office forecast is so much lower than the other seasonal Atlantic forecasts. I believe that the GloSea model has high enough resolution to do as good a job as the other seasonal hurricane forecasts this year, but it's hard to make an informed judgment until their research results are published. The GloSea forecast is based on sound science, though, and does call into question whether or not the other seasonal forecasts are forecasting unrealistically high levels of hurricane activity in the Atlantic this year. I think that is probably the case, and a better forecast can be made by averaging together the four models into a consensus forecast. Consensus forecasts are difficult to beat, and the consensus of the CSU, NOAA, TSR, and UK Met Office forecasts yields a prediction of 13 more named storms this year, for a total of 15.

The future of seasonal hurricane forecasts
The future of seasonal hurricane forecasts using global dynamical computer models is bright. A group using the European Center for Medium Range Weather Forecasting (ECWMF) model is also experimenting with some promising techniques using that model. Models like the GloSea and ECMWF will only get better as increased computer power and better understanding of the atmosphere are incorporated, necessitating less use of "fudge" factors based on historical hurricane patterns. If human-caused climate change amplifies in coming decades, statistical seasonal hurricane forecasts like the CSU's may be limited in how much they can be improved, since the atmosphere may move into new patterns very unlike what we've seen in the past 100 years. It is my expectation that ten years from now, seasonal hurricane forecasts based on global computer models such as the UK Met Office's GloSea will regularly out-perform the statistical forecasts issued by CSU.

Bill Proenza to appear on Thursday's Barometer Bob show
Thursday night June 21, new NHC director Bill Proenza will be the guest on the Barometer Bob Show. You can listen at barometerbobshow.com, or dial in via their toll-free number 1-866-931-8437 (1-866-WE1THER). If you want to ask him a question, you can do so using their Storm Chat web page.

Tropical Outlook
A cold front pushing off the East Coast of the U.S. on Thursday could trigger formation of a tropical depression by Friday or Saturday over the Gulf Stream waters between Daytona Beach, Florida and Cape Hatteras, North Carolina. Several of the computer models are forecasting that a weak low pressure system will form by Friday in this region. However, there will be a lot a wind shear close by, which may make any storm storm that does form subtropical or non-tropical. It is uncertain where such a storm might move, since steering currents will be weak. I'll have an update on this situation by Friday at the latest.

Jeff Masters

NHC director Bill Proenza under fire

By: JeffMasters, 2:04 PM GMT on June 18, 2007

New National Hurricane Center director Bill Proenza is in hot water for his outspoken criticism of his bosses, according to Miami Herald stories published in the past few days. The acting head of the National Weather Service, Mary Glackin, visited his office in Miami Friday and handed him a three-page letter of reprimand. Proenza shared the contents of the letter with his staff and the media, a pretty gutsy move for a guy just appointed to the job. However, Proenza's boss, Ms. Glackin, is on the job for just a few more months--on September 2, Jack Hayes takes over as boss of the National Weather Service. Proenza can probably get away with his criticism of his bosses while there a major shake up at the top. See the View From the Surface blog this week for further speculations, and for any follow-up articles that might be published on this topic.


Figure 1. The NASA QuikSCAT satellite. Image credit: NASA Earth Observatory.

Replacement for the aging QuikSCAT satellite?
Proenza has been particularly outspoken in his desire to see a replacement for the aging QuikSCAT satellite, which measures surface winds over remote ocean areas, and has been credited with improving 72-hour hurricane track forecasts by 16%. His comments may be having an effect. On May 24, the improved Hurricane Tracking and Forecasting Act of 2007 (Senate Bill S. 1509) was introduced before the Senate. The bill, introduced by Sen. Landrieu, D-LA, and co-sponsored by John Kerry and Florida's two senators, asks for $375 million to build a replacement for the QuikSCAT satellite. Bravo to Mr. Proenza for speaking out on this important issue! Some excepts from the bill:

(5) The QuikSCAT satellite was built in just 12 months and was launched with a 3-year design life, but continues to perform per specifications, with its backup transmitter, as it enters into its 8th year--5 years past its projected lifespan.

(6) The QuikSCAT satellite provides daily coverage of 90 percent of the world's oceans, and its data has been a vital contribution to National Weather Service forecasts and warnings over water since 2000.

(7) Despite its continuing performance, the QuikSCAT satellite is well beyond its expected design life and a replacement is urgently needed because, according to the National Hurricane Center, without the QuikSCAT satellite--

(A) hurricane forecasting would be 16 percent less accurate 72 hours before hurricane landfall and 10 percent less accurate 48 hours before hurricane landfall resulting in--

(i) with a 16 percent loss of accuracy at 72 hours before landfall, the area expected to be under hurricane danger would rise from 197 miles to 228 miles on average; and

(ii) with a 10 percent loss of accuracy at 48 hours before landfall, the area expected to be under hurricane danger would rise from 136 miles to 150 miles on average; and

(B) greater inaccuracy of this type would lead to more `false alarm' evacuations along the Gulf Coast and Atlantic Coast and decrease the possibility of impacted populations sufficiently heeding mandatory evacuations.


The bill has been referred to the Senate Committee on Commerce, Science, and Transportation, and awaits consideration there. The Chair of that committee is Senator Inouye from hurricane-prone Hawaii, so the bill has a decent chance of making it out of committee to the Senate floor. If your senator is on the committee, please write them to let them know what you think about the bill:

Democrats:
Chairman Daniel K. Inouye (HI)
John D. Rockefeller, IV (WV)
John F. Kerry (MA)
Byron L. Dorgan (ND)
Barbara Boxer (CA)
Bill Nelson (FL)
Maria Cantwell (WA)
Frank R. Lautenberg (NJ)
Mark Pryor (AR)
Thomas Carper (DE)
Claire McCaskill (MO)
Amy Klobuchar (MN)

Republicans:
Vice Chairman Ted Stevens (AK)
John McCain (AZ)
Trent Lott (MS)
Kay Bailey Hutchison (TX)
Olympia J. Snowe (ME)
Gordon H. Smith (OR)
John Ensign (NV)
John E. Sununu (NH)
Jim DeMint (SC)
David Vitter (LA)
John Thune (SD)

There is no activity in the tropical Atlantic worth mentioning, and none of the computer models are forecasting any development over the coming week. I'll have a new blog on Wednesday.

Jeff Masters

Politics

June hurricane season outlook; Bahamas disturbance fizzles

By: JeffMasters, 3:12 PM GMT on June 16, 2007

An area of disturbed weather with heavy thunderstorm activity is over the Bahama Islands, and shows no signs of organization. The system crossed Cuba last night, brushed South Florida, and brought heavy rains of 2-4" inches over these areas. The system will bring another 1-2" to the Bahamas before heading northeast out to sea. The disturbance is now entering an area with very high wind shear of 30 knots, and is no longer a threat to develop into a tropical depression. The system could develop into an extratropical storm. No Hurricane Hunter missions are planned into the system, and NHC no longer thinks highly enough of it to offer their suite of early model tracks. There are no other threat areas to discuss, and none of the models are showing any new developments over the coming week. I'll repost my June hurricane season outlook below, and have a new blog on Monday!

Jeff Masters

Last half of June climatology
The last half of June is usually one of the quietest portions of hurricane season. In the 12 years since the current active hurricane period began in 1995, only four tropical storms formed in the last half of June. Thus, recent history gives us a 33% chance of a last-half-of-June named storm. None of those four storms since 1995 became a hurricane, and hurricanes are quite rare in June. Only one major hurricane has has made landfall in June--Category 4 Hurricane Audrey of 1957, which struck the Texas/Louisiana border area on June 27 of that year, killing 550. The primary breeding grounds for last half of June tropical storms is the western Gulf of Mexico (Figure 1).


Figure 1. Tracks of all tropical storms and hurricanes since 1851 that formed June 16-30. The western Gulf of Mexico is the preferred location for storm formation in late June. Interestingly, the eastern Gulf of Mexico sees the most early June storms.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) have remained about 0.5-1.0 C above average over the tropical Atlantic over the past two weeks. An area of cooler than average SSTs that surrounded Florida in early June has shrunk, and the entire Gulf of Mexico is now warmer than average. However, while SSTs are above normal, they are still far cooler than the peak temperatures that occur in August-October. This will limit the regions where tropical storm formation can occur this month to the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida, where water temperatures are warmest (Figure 2). June storms typically form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance. African tropical waves, which serve as the instigators of about 85% of all major hurricanes, are usually too far south in June to trigger tropical storm formation.


Figure 2. Sea Surface Temperature (SST) departure from average for June 14, 2007. Image credit: NOAA.

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 3) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. As we can see, there is less heat energy available this year than in 2005, which recorded the highest SSTs and TCHP ever measured in the tropical Atlantic. I expect that the TCHP will continue to remain below 2005 levels this year, so we should not see as many intense hurricane as we saw in 2005.


Figure 3. Tropical Cyclone Heat Potential (TCHP) for June 14 2005 (top) and June 14 2007 (bottom). TCHP is a measure of the total heat energy available in the ocean. Record high values of TCHP were observed in 2005. TCHP this year is still quite high, but lower than in 2005. Image credit: NOAA/AOML.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart.

Wind shear over the past 11 days (Figure 4, top image) has been above 20 knots over most of the breeding grounds for June tropical storms--the Gulf of Mexico, Western Caribbean, and Bahama waters. While the shear has been below average (Figure 4, bottom image), any wind shear above 20 knots is high enough to discourage tropical storm formation. This is very typical for June, when the jet stream is still very active and quite far south. The jet stream will gradually weaken as summer progresses, bringing lower wind shear and greater chances for tropical storm formation. The extreme southwestern Caribbean has seen shear below 10 knots, but no tropical waves or remains of old cold fronts have moved into this region to trigger tropical storm formation. The latest two-week forecast from the GFS model predicts that wind shear will be near normal levels across the Caribbean, Gulf of Mexico, and tropical Atlantic for the remainder of June.


Figure 4. Top: Average wind shear over the past 11 days. Wind shear is the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude) in meters per second (multiply by two to get the approximate wind shear in knots). In most circumstances, wind shear above 20 knots (10 m/s, the blue colors in the top image) will act to inhibit tropical storm formation. Wind shear below 12 knots (6 m/s, the orange colors) is very conducive for tropical storm formation.
Bottom: Departure of wind shear from average for the past 11 days in meters per second. Note that wind shear has been below average over most of the tropical Atlantic and Gulf of Mexico over the past 11 days.

Dry air and African dust
It's too early to concern ourselves with dry air and dust coming off the coast of Africa, since these dust outbreaks don't make it all the way to the June tropical cyclone breeding grounds in the Western Caribbean and the Gulf of Mexico. Developing storms do have to contend with dry air from Canada moving off the U.S. coast, though.

Steering currents
The steering current pattern for the first half of June featured a pattern much like we saw in 2006, with an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. I expect this pattern to continue for the remainder of June, and the troughs should be frequent enough and strong enough to recurve any tropical storms of hurricanes that penetrate north of the Caribbean Sea. Steering current patterns are not predictable more than about two weeks in advance, and there is no telling if we are in for a repeat of the favorable 2006 steering current pattern that recurved every storm out to sea. It is encouraging to note that in 2006 the steering current pattern locked into place in late May and stayed that way for almost the entirety of the hurricane season. The atmosphere often stays locked in to a particular steering pattern for an entire summer.

Summary
Recent history suggests a 33% chance of a named storm occurring in the second half of June. Given that the current SST pattern and two-week wind shear forecast look fairly typical for June, I'll go with a 30% chance of a named storm forming during the last half of June.

Jeff Masters

June hurricane season outlook

By: JeffMasters, 7:37 PM GMT on June 15, 2007

An area of disturbed weather with heavy thunderstorm activity has developed along a broad trough of surface low pressure in the western Caribbean between Mexico's Yucatan Peninsula and Cuba. Satellite imagery shows a steadily increasing amount of heavy thunderstorm activity, but no signs of a surface circulation. NHC canceled the Hurricane Hunter flight scheduled for this afternoon, and has not scheduled a mission for Saturday.

NHC no longer thinks highly enough of this system to offer their suite of early model tracks, but the latest runs of the GFS, NOGAPS, and UKMET models all indicate that the disturbance will move north then northeastward over the weekend, bringing heavy rains of 2-4 inches over Central Cuba, extreme South Florida, and the northwest Bahama Islands. Some isolated amounts of up to 6 inches are possible over Cuba and the Bahamas. All of these models indicate the possibility that a tropical or subtropical depression could form by Sunday near South Florida or the Bahamas. There is enough wind shear that an extratropical storm could form, instead, though. Wind shear over the disturbance has decreased from 20-25 to 10-20 knots today, and is forecast to remain at similar levels for the next 48 hours. There is some dry air one can see on Water vapor satellite loops over the western Caribbean and southern Gulf of Mexico slowing development of the system, and this will continue to be a factor that will slow development over the next two days. Surface pressures are not falling over the region, and thus any development is going to be slow to occur. I give the system a 20% chance of becoming a depression. Wind shear is a very high 20-40 knots from central Florida northwards, which should act to keep the top winds of any storm that does form below 50 mph.

Last half of June climatology
The last half of June is usually one of the quietest portions of hurricane season. In the 12 years since the current active hurricane period began in 1995, only four tropical storms formed in the last half of June. Thus, recent history gives us a 33% chance of a last-half-of-June named storm. None of those four storms since 1995 became a hurricane, and hurricanes are quite rare in June. Only one major hurricane has has made landfall in June--Category 4 Hurricane Audrey of 1957, which struck the Texas/Louisiana border area on June 27 of that year, killing 550. The primary breeding grounds for last half of June tropical storms is the western Gulf of Mexico (Figure 1).


Figure 1. Tracks of all tropical storms and hurricanes since 1851 that formed June 16-30. The western Gulf of Mexico is the preferred location for storm formation in late June. Interestingly, the eastern Gulf of Mexico sees the most early June storms.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) have remained about 0.5-1.0 �C above average over the tropical Atlantic over the past two weeks. An area of cooler than average SSTs that surrounded Florida in early June has shrunk, and the entire Gulf of Mexico is now warmer than average. However, while SSTs are above normal, they are still far cooler than the peak temperatures that occur in August-October. This will limit the regions where tropical storm formation can occur this month to the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida, where water temperatures are warmest (Figure 2). June storms typically form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance. African tropical waves, which serve as the instigators of about 85% of all major hurricanes, are usually too far south in June to trigger tropical storm formation.


Figure 2. Sea Surface Temperature (SST) departure from average for June 14, 2007. Image credit: NOAA.

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 3) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. As we can see, there is less heat energy available this year than in 2005, which recorded the highest SSTs and TCHP ever measured in the tropical Atlantic. I expect that the TCHP will continue to remain below 2005 levels this year, so we should not see as many intense hurricane as we saw in 2005.


Figure 3. Tropical Cyclone Heat Potential (TCHP) for June 14 2005 (top) and June 14 2007 (bottom). TCHP is a measure of the total heat energy available in the ocean. Record high values of TCHP were observed in 2005. TCHP this year is still quite high, but lower than in 2005. Image credit: NOAA/AOML.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart.

Wind shear over the past 11 days (Figure 4, top image) has been above 20 knots over most of the breeding grounds for June tropical storms--the Gulf of Mexico, Western Caribbean, and Bahama waters. While the shear has been below average (Figure 4, bottom image), any wind shear above 20 knots is high enough to discourage tropical storm formation. This is very typical for June, when the jet stream is still very active and quite far south. The jet stream will gradually weaken as summer progresses, bringing lower wind shear and greater chances for tropical storm formation. The extreme southwestern Caribbean has seen shear below 10 knots, but no tropical waves or remains of old cold fronts have moved into this region to trigger tropical storm formation. The latest two-week forecast from the GFS model predicts that wind shear will be near normal levels across the Caribbean, Gulf of Mexico, and tropical Atlantic for the remainder of June.


Figure 4. Top: Average wind shear over the past 11 days. Wind shear is the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude) in meters per second (multiply by two to get the approximate wind shear in knots). In most circumstances, wind shear above 20 knots (10 m/s, the blue colors in the top image) will act to inhibit tropical storm formation. Wind shear below 12 knots (6 m/s, the orange colors) is very conducive for tropical storm formation.
Bottom: Departure of wind shear from average for the past 11 days in meters per second. Note that wind shear has been below average over most of the tropical Atlantic and Gulf of Mexico over the past 11 days.

Dry air and African dust
It's too early to concern ourselves with dry air and dust coming off the coast of Africa, since these dust outbreaks don't make it all the way to the June tropical cyclone breeding grounds in the Western Caribbean and the Gulf of Mexico. Developing storms do have to contend with dry air from Canada moving off the U.S. coast, though.

Steering currents
The steering current pattern for the first half of June featured a pattern much like we saw in 2006, with an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. I expect this pattern to continue for the remainder of June, and the troughs should be frequent enough and strong enough to recurve any tropical storms of hurricanes that penetrate north of the Caribbean Sea. Steering current patterns are not predictable more than about two weeks in advance, and there is no telling if we are in for a repeat of the favorable 2006 steering current pattern that recurved every storm out to sea. It is encouraging to note that in 2006 the steering current pattern locked into place in late May and stayed that way for almost the entirety of the hurricane season. The atmosphere often stays locked in to a particular steering pattern for an entire summer.

Summary
Recent history suggests a 33% chance of a named storm occurring in the second half of June. Given that the current SST pattern and two-week wind shear forecast look fairly typical for June, and we have a system out there now that has a small chance of becoming a named storm, I'll go with a 40% chance of a named storm forming during the last half of June.

Jeff Masters

Western Caribbean disturbance could bring heavy rains to Florida

By: JeffMasters, 1:55 PM GMT on June 15, 2007

An area of disturbed weather (94L) with heavy thunderstorm activity has developed in the western Caribbean between Mexico's Yucatan Peninsula and Cuba. This disturbance has the potential to form into a tropical depression by Sunday as it drifts northwards into the Gulf of Mexico. Wind shear over the northwest Caribbean is a not-so-healthy-for-development 20-25 knots, but is forecast to decrease somewhat over the next 48 hours. There is some dry air over the western Caribbean and southern Gulf of Mexico, but water vapor satellite loops show that the thunderstorm activity starting to fire up in association with the disturbance is steadily moistening the atmosphere. However, surface pressures are rising over the region, and thus any development is going to be slow to occur. The 7:21am EDT QuikSCAT satellite wind map show no surface circulation, and neither do satellite loops. Top winds from QuikSCAT were in the 20-30 mph range. However, winds were only about 15 mph at the Yucatan Basin buoy, and this is more representative of the winds associated with the disturbance.


Figure 1. Visible satellite image of the western Caribbean disturbance.


Figure 2. Early model tracks for the western Caribbean disturbance.

None of the computer models forecast that this system will become a tropical storm, but the GFS model is indicating that an extratropical storm will form from this system early next week once it moves over Florida. The situation looks similar to what happened with Tropical Storm Barry, and we could get a hybrid subtropical storm forming in the Gulf on Saturday or Sunday, as the system passes over some very deep warm waters associated with the "Loop Current" that feed the Gulf Stream. There will be a lot of wind shear (20-40 knots) over the northern Gulf of Mexico over the next seven days, which should prevent any system that forms from having winds stonger than about 60 mph. A tropical, subtropical or extratropical storm with winds topping out at 50 mph is 20% probable, though, and Florida may be the beneficiary of another good rain-making storm.

A Hurricane Hunter flight was scheduled to visit the system at 2pm EDT this afternoon, but has been canceled. The flight has not been re-scheduled for Saturday. I'll have an update on this system this afternoon, and will include my rest of June outlook for hurricane season.

Jeff Masters

F5: a book review

By: JeffMasters, 1:28 PM GMT on June 13, 2007

F5: Devastation, Survival, and the Most Violent Tornado Outbreak of the 20th Century tells a story from the world's most violent tornado outbreak on record--the April 4, 1974 Super Outbreak. The Super Outbreak featured the most tornadoes ever recorded in a single day, 148, and also had an unprecedented number of violent F4 and F5 tornadoes--six F5 tornadoes and 24 F4 tornadoes (for comparison, the past five years have had one F5 tornado and 15 F4 tornadoes.)

The book has some excellent material discussing the "how" of tornado formation, plus an entire chapter on the life and pioneering research done by tornado researcher Dr. Theodore Fujita (Dr. Tornado). Author Mark Levine definitely did his homework, talking to many of the leading tornado researchers while writing the book. However, F5 is primarily focused on the people who lived in Limestone County, Alabama--a rural area 20 miles west of Huntsville. We get an in-depth portrayal of the lives of about 30 residents affected by the tornado before, during, and after the storm. Many chapters are spent building up to the tornadoes, painting a detailed picture of what life was like in rural Alabama for these people in the early 1970s. Levine is a gifted writer, and for those interested in the human dimensions of this great tornado disaster, this book is for you. Also, readers who appreciate poetry (the author has written three books of poems, will enjoy Levine's flowery, wordy descriptions:

The fear instilled by tornadoes, and the fascination with them, is beyond rational accounting; they are the weather watcher's equivalent of charismatic megafauna. Their aura is not difficult to fathom. Descending suddenly, menacingly, and without reliable warning, the tornado serves as a near-primal expression of the mysterious and fraught relationship between individuals and the skies above them.

The book has some rather astounding "truth is stranger than fiction" passages. The eyewitness descriptions by the survivors of their horrifying moments flying through the roaring debris-filled air as a monstrous F-5 tornado rips through their homes are particularly riveting. The most amazing part about the events in Limestone County that night was that TWO violent tornadoes--an F4 and an F5--ripped through several hours apart, hitting some of the exact same places. Levine paints a harrowing and unforgettable picture of what it was like to live through the terror of the two tornadoes. Another excerpt:

What Jerry saw was strange and wondrous. Clouds were riding across open fields to the west, moving just like clouds do across the sky. As the clouds passed a steel TVA tower, it snapped out of the ground, and began rolling across the field. A moment later, a second tower was toppled. To Jerry, the scene resembled something out of a cartoon, with the 120-foot high girders skipping like tumbleweeds.


What I didn't like about the book
While F5 is well written and absolutely fascinating in sections, I thought the book was too verbose and took too long to get to the action. I found myself skipping over some sections. The book also introduced too many characters to follow, and I got confused about who was whom. One of my many character flaws is a disinterest in poetry, and I found that the dense, flowery, poetic language of Levine interfered with my desire to see the story moved forward and straightforward science to be presented. The tornadoes don't start their rampage through Limestone County until page 119 of this long, 276-page book, which was too long to wait for my impatient blood. If you want to read a fast-paced true-life tornado drama, pick up a copy of Nancy Mathis' excellent book Storm Warning, about the May 3, 1999 Oklahoma City tornado, which I reviewed earlier this year.

Overall, I give F5 2.5 stars out of 4. If you're a poetry fan, this book deserves a higher rating. F5 was published in May 2007, and is $17.13 at amazon.com.

I'll be back Friday with my bi-monthly 2-week outlook for hurricane season. The tropics are quiet, and the models are forecasting conditions will remain quiet into next week.

Jeff Masters

Book and Movie Reviews

Quiet tropics; aftermath of Gonu

By: JeffMasters, 1:34 PM GMT on June 11, 2007

The tropical Atlantic continues to be quiet, which is typical for this time of year. Wind shear across the June breeding grounds for June tropical systems--the Gulf of Mexico, Western Caribbean, and Bahamian waters--is expected to remain high this week, which should discourage any tropical storms from forming. None of the computer models are forecasting any tropical development this week. Unless there's a significant change, I won't discuss the tropics until Friday, when I'll post my bi-monthly Atlantic hurricane season outlook.

Tropical Cyclone Gonu
While I was away on vacation last week, a rather remarkable Category 5 cyclone developed in the Arabian Sea and struck Oman and Iran. Gonu is the first Category 4 or higher storm recorded in the Arabian Sea since the satellite era began in 1970. The last significant tropical cyclone to affect Oman was in 1890, when a storm hit the Gulf of Oman coast and Muscat, killing 700 people. Lesser cyclones affected the area in 1945 and 1977. The View From the Surface blog has an excellent summary of the aftermath of Gonu.


Figure 1. Rainfall estimates from NASA's TRMM satellite for the 8-day period May 31-June 7, 2007. Some regions of Oman and Iran received 200 mm (8 inches) of rain from the storm, equal to double their average annual rainfall. Image credit: NASA Earth Observatory.

Jeff Masters

Grading NHC's Tropical Weather Outlook

By: JeffMasters, 4:33 PM GMT on June 06, 2007

The National Hurricane Center's Tropical Weather Outlook (TWO) is a text-only product that rates the potential of disturbed areas of weather to turn into tropical depressions or tropical storms. The outlooks are issued four times daily, at 5am, 11am, 5pm, and 11pm EDT. I've found them to be an excellent guide to what to watch out for. But how accurate are these outlooks? To find out, Jamie Rhome and Dan Brown, who are two of the hurricane specialists that write the Tropical Weather Outlook, verified the accuracy of all the outlooks issued in 2005 and 2006. They used a three-tiered classification of threat based on the following language appearing in the TWO:

High: "A tropical depression could form tonight or the next day."

Medium: "Some slow development is possible."

Low: "Tropical storm formation is not expected."


These forecasts were then graded by looking at the "best track" database of Atlantic hurricanes and seeing if a tropical depression formed within 48 hours of each TWO issued. The results, shown below, reveal that for the Atlantic in the years 2005 and 2006:

-When the TWO said, "A tropical depression could form tonight of the next day," a depression formed within 48 hours 53% of the time.

-When the TWO said, "Some slow development is possible," a tropical depression formed within 48 hours about 20% of the time.

-When the TWO said, "Tropical storm formation is not expected," a tropical depression formed within 48 hours only 3% of the time.




Figure 1. Verification of the Atlantic and Eastern Pacific Tropical Weather Outlooks issued in 2005 and 2006. Image credit: Jamie Rhome and Dan Brown, National Hurricane Center.

Jeff Masters

Severe Cyclone Gonu Prepares to Strike the Gulf of Oman

By: JeffMasters, 5:34 AM GMT on June 05, 2007

An unusual event is happening over the next 48 hours, as the first tropical cyclone with hurricane-force winds, and major hurricane-force winds at that, is approaching the Gulf of Oman, to strike the eastern coast of Oman, curve northward, and make landfall on the coast of Iran. In the tropical cyclone best tracks and the modern era of weather satellites, there is no record of such an occurrence.

Today, Steve Gregory and I will be guest-hosting the blog, while Jeff is on vacation, to provide current information on Severe Cyclone Gonu. I'll provide some background on the areas that are currently forecast to be in the path of this dangerous cyclone, followed by Steve's Monday evening surge forecast and assessment based on the most recent JTWC track and intensity forecast, which currently calls for sustained winds of 115 kt when first passing near the coastline of Oman.

Updates during the day will be posted on my blog, The View From the Surface.

As I write this it is late in the evening in the central US, but the day has already begun in the Middle East. Distant cirrus from Gonu have already started to cloud the Gulf of Oman, and over the course of the day there, conditions will deteriorate along the eastern coast of Oman as the tropical cyclone approaches. Overnight, the core of Gonu will approach the tip of Oman, with the eye passing offshore just before dawn, and the bulk of the surge occuring along the eastern coast some time shortly before that. By midday the next day the worst of the storm will have passed the southernmost portion of the coast, and the core of the storm will be directly east of Muscat, the capital of Oman, home to over half a million people. Right now the forecast has the storm passing just offshore, but if the track shifts further east, the most damaging winds of the cyclone will remain over water. This will lessen the damage to Oman, but will likely result in a higher intensity when making landfall in Iran.

--Margie Kieper

* * * * * * *

Those who live along the Gulf of Mexico are well aware of what it means for a major hurricane to make landfall. Even if they've never experienced it themselves, they have relatives or members of their community who have experienced it. And in many places they can see the damage that remains.

Imagine that you live directly on the Gulf, but in a place where it hardly ever rains, and where a hurricane has never hit, for at least a generation -- for more than sixty years. Your community and many like yours are situated not only directly on the water, but near or in large dry riverbeds on the coastal plain, which is a narrow strip of sandy shoreline that is the dropoff for the three-thousand-foot mountain range behind it. Even many of the roads up into the mountains are in these dry riverbeds, which course through deep canyons as they rise into the heights. You don't have any idea what it might mean to experience winds of over 100 miles per hour, whipping up sand, and torrential rain against these mountains that can turn the riverbeds into conduits for dangerous flash floods. And you don't have any idea what storm surge is, and can't conceive of wind-driven high waves that could break against the shoreline and leave nothing behind.

This is the eastern coast of Oman, where communities line the shoreline which is shortly going to be experiencing a major hurricane. We can only hope that the danger is understood and that all of these communities have evacuated to higher ground and a safer location.

Below are two images of the city of Sur, showing how the community is built right along the water's edge:

Sur


closeup of Sur


The first image below shows one of the large winding dry riverbeds, and the second close-up shows a village built right where this riverbed empties into the gulf.

dry riverbed


community built in riverbed


These images show an industrial facility on the shoreline right at the tip of southeastern Oman, with an airstrip and a small community -- all of which could be gone in twenty-four hours, from surge, if the storm passes close to this area as currently forecast.

southeastern tip of Oman


closeup of southeastern tip of Oman


* * * * * * *

Steve Gregory's Monday Evening Forecast for Gonu

Severe Cyclone GONU in the Arabian Sea is currently heading NW at 14KTS (Faster than the JTWC Forecast) and is located 135NM SE of the eastern most 'tip' of Oman, and 180NM SE of Muscat. The storm is now a very strong CAT 4 - with an estimated pressure of 904mb, and wind gusts to 155Kts.

Based on imagery over the last 6 hours - the storm is under-going an Eyewall Replacement cycle, and so the first early morning VIS image (right) shows the eye is now covered with cirrus. As a new eyewall is developing (based on Micro-wave imagery) and will complete this cycle right about the time it gets to the Oman Gulf.

The track the storm takes as it nears the Oman coast is extremely critical in terms of intensity as it is entering the Gulf - and how severe the damage will be. There ocean heat content of the water on the SE FACING side of Oman is lower - and if the storm travels close to that location (as shown on the NAVY chart) the storm will likely weaken further during the day to a low end CAT 3, and then hit the Iran coast as a strong CAT 1 on Wednesday.

If the storm tracks 50-100NM NORTH of the coast as it enters the Gulf of Oman - though the water is shallower there, the SST's are very high (32degC) and with the storm further away from land, and over very warm water - it is likely to hold onto CAT 3 intensity for an additional 4-6 hours as it moves NW.

There is a large oil facility and large airport located right at the eastern 'tip' of Oman - and I counted at least 6 major 'ports' on Satellite imagery along the Oman coast up to 100 miles WNW of Muscat.

On the opposite side of the Gulf is the Iranian coast - with numerous 'cove inlets' each with loading docks and port facilities. At least 9 facilities I could count from the Iran/Pakistan border west to the area I show landfall (Magenta Arrow on the diagram below). Offshore platforms were also seen in a few locations.

Steve Gregory Gonu surge forecast


The Storm surge shown (10-15 ft) will almost certainly hit the Iran coast - even if the storm weakens to a strong CAT 2 late Tuesday (NY time). The Eastern tip of Oman will likely also experience 10-15 foot surge due to the close proximity of the storm track. Further up the Gulf, before reaching the Straits of Hormuz - storm surge heights of 1-4 feet are expected on the Oman side, and 4-possibly 6 feet on the Iranian side near the entrance to the Straits. Significant wave heights will be 20-30 feet, dropping to 15 feet near the Straits.

This is an unprecedented event. NO CYCLONE has ever entered the Gulf of Oman. And there are no custom 'storm surge' models available for that area. This forecast is based on my experience and subjective analysis of the seabed slope and storm surge interaction with the sea floor. Considering the region has never experienced a hurricane, let alone a strong one it is highly unlikely the loading facilities or platforms were constructed to withstand the forces - both wave action and wind force - that they will experience. Significant, damage will occur. How much long term damage, and the volumes associated with it - can not be determined at this time.

--Steve Gregory

Beneficial Barry

By: JeffMasters, 4:43 PM GMT on June 03, 2007

Tropical Storm Barry is no more. Its remnants, now an extratropical storm with top winds of 40 mph over the ocean, are over the Mid-Atlantic coast, moving north-northeastward at 10 mph. Barry's remnants are expected to bring 1-3 inches of rain along the Mid-Atlantic and New England states through Monday. Was Barry really a tropical storm? I think it should have been named "Subtropical Storm Barry", and I hope NHC looks at the storm carefully to consider redesignating it after the season is over. Read Margie Kieper's View From the Surface blog for more on this.

On Saturday, Barry brought up to seven inches of rain to drought-parched Florida, including an official 6.99" to West Palm Beach, 4.07" to Jacksonville, 5.91" to Savannah Georgia, and 3.17" to Tampa. Barry's rains probably provided tens of millions of dollars of benefit--quite the opposite of what we're used to saying about tropical storms! The fire area near the Florida-Georgia border got between 1-5 inches of rain from Barry, which has dampened but not extinguished the fires. Barry's rains also helped a bit with the Florida drought. However, Barry's rains were only 1-2 inches over central Florida, and they need about 30 inches of rain to pull them out of drought conditions. The summer rainy season typically begins in June, so there is hope that substantial rains are on the way. There doesn't appear to be much rain coming this week, though.


Figure 1. Total rainfall from Barry for northern Florida, estimated by radar.

June outlook
My outlook for the first two weeks of June was posted Friday. I don't see anything on the horizon for the remainder of this week--wind shear is expected to be high most of this week over the favored breeding grounds for June storms--the Gulf of Mexico and Western Caribbean. Wind shear may drop enough over the Western Caribbean early next week to allow tropical storm formation, but that is too far in the future to guess at the probability of such an event.

This will be my last "live" blog until Monday June 11; it's time to grab a week of summer vacation while the tropics are quiet. I'm off to see Niagara Falls and the "Grand Canyon of the East", New York's awesome Letchworth State Park. I hope to get some good waterfall rainbow shots to add to my wunderphotos. I've written two canned blogs that will be posted Tuesday and Friday while I'm gone:

Tuesday--We've all used NHC's Tropical Weather Outlook, which most often this time of year says, "Tropical cyclone formation is not expected during the next 48 hours." How accurate are these outlooks? I'll present some verification statistics from 2005 and 2006.

Friday--The NHC made it's best track forecasts ever last year. How good are their forecasts now? Which of the various computer models performed the best last year? I'll have a breakdown of the numbers.

Arrogance
Our Climate Change blog by Dr. Ricky Rood has an interesting commentary on what the chief of NASA said last week in an NPR interview when asked, "Do you have any doubt that climate change is a problem that mankind has to wrestle with?"

Strongest tropical cyclone ever seen in Arabian Sea
Follow The View From the Surface blog this week to track Tropical Cyclone Gonu. Gonu is the strongest storm ever seen in the Arabian Sea, and could cause big trouble for the Persian Gulf oil rigs and tankers.

Jeff Masters

Fire

Barry weakens, douses Florida with needed rains

By: JeffMasters, 2:14 PM GMT on June 02, 2007

Tropical Storm Barry is steadily weakening as it races towards the Florida coast. Winds have decreased to 40 mph, as observed by the 9:30am EDT Hurricane Hunter report, which found winds at 1,500 altitude of 47 mph. The pressure has risen 2 mb in the past two hours, and now stands at 1002 mb. Barry is embedded in a zone of strong wind shear--about 30 knots. This shear ripped away most of Barry's deep thunderstorm activity last night, and pushed these storms over the Florida Peninsula. Satellite loops shows that some heavy thunderstorm activity has returned near the center of circulation, so the shear has not been able to totally destroy the storm yet. As Barry continues today over cooler waters, it should continue to weaken, and residents of Florida should expect only minor wind damage. I doubt any station will experience sustained winds of tropical storm strength (39 mph), although gusts of 50-55 mph are likely. The main threat from Barry will be isolated tornadoes that could spin up in some of the heavier thunderstorms over land. The storm surge may cause minor flooding in the Tampa Bay area. Currently, tides are running a foot or two above normal there, and will increase with a persistent onshore wind to 3 to 5 feet above normal this afternoon from the Tampa Bay area northward to Citrus County and 1 to 3 feet south of Tampa Bay and Levy County.

Barry will do far more good than harm--the storm has already dumped 1-5 inches of rain over most of Florida, with more rain to come. Heavy rain from Barry will affect the Carolinas on Sunday, and could cause some local flooding problems there. However, Barry will lose its tropical storm status after crossing Florida, and is not a threat to reintensify after crossing into the Atlantic Ocean.


Figure 1. Total rainfall from the Tampa Bay radar.

A sign of things to come?
The hurricane season of 2007 is in third place for the earliest year that the second named storm occurred. The record is held by 1887, when the second named storm formed on May 17. Second place is held by 1908, when the second storm of the year formed on May 26.

There is no relationship between high activity early in hurricane season and high activity during the main August-October peak of the season. For example, the 1908 hurricane season turned out to be an ordinary season with 10 named storms, 6 hurricanes, and one intense hurricane.

June outlook
My outlook for the first two weeks of June was posted yesterday.

Radio play
National Public Radio's The Story program aired a 30-minute interview with me yesterday about my flight into Hurricane Hugo in 1989. The MP3 of the interview is at http://thestory.org/archive/the_story_263_Hunting _Hurricanes.mp3.

Jeff Masters

Fire

A June 1 surprise: Tropical Storm Barry

By: JeffMasters, 9:25 PM GMT on June 01, 2007

The hurricane season of 2007 officially began today, and we officially have our second surprising named storm of the season--Tropical Storm Barry. Barry is highly unusual in that it developed in the presence of strong wind shear--about 20-40 knots. I've never seen a tropical storm form under more than about 25 knots of wind shear. Satellite loops show a well-defined circulation to the west of Key West, and heavy thunderstorm activity popping up on the north side of the center. Barry is over the warm 82F waters of the Loop Current, and will gradually traverse over colder waters as it moves north and then north-northeast over the next day. The circulation of Barry is now visible on the Key West radar. Pulaski Shoal Light just to the northeast of Barry's center recorded sustatined winds of 35 mph, gusting to 40mph, at 2pm EDT today.

The Hurricane Hunters are still in Barry, and found that the pressure continues to drop--997 mb at 6:30pm EDT. The winds are also increasing, with the top winds at 77 mph at flight level of 1,500 feet at 5pm EDT. This corresponds to peak surface winds of about 60 mph. However, these winds are not representative of the storm, and likely occurred in the outflow from the strongest thunderstorm near the center. NHC is justified in bringing the intensity up to just 50 mph in their 8pm advisory.

I don't expect Barry will intensify to a hurricane, due to increasing wind shear and cooler waters underneath. Barry should mostly be a blessing for Florida, who can use the 3-6 inches of rain the storm is likely to bring. Some storm surge flooding may occur along the same stretch of coast affected by Tropical Storm Alberto last year. However, no damage was reported due to Alberto's storm surge, and Barry's should be roughly the same magnitude. Perhaps the greatest threat from Barry will be tornadoes that could form Saturday afternoon over Florida.

Another Hurricane Hunter aircraft is scheduled to investigate Barry at 8am EDT.


Figure 1. Total rainfall from the Tampa Bay radar.

A sign of things to come?
The hurricane season of 2007 is in second place for the earliest year that the second named storm occurred. The record is held by 1887, when the second named storm formed on May 17. Third place is held by 1934, when the second storm of the year formed on June 4. The second storm of 1934 was also the worst June hurricane on record. It hit Central America as a Category 1 hurricane, dropping up to 25 inches of rain on Honduras, triggering landslides that killed 3,000 people.

There is no relationship between high activity early in hurricane season and high activity during the main August-October peak of the season. For example, the 1934 hurricane season turned out to be an ordinary season with 11 named storms, 6 hurricanes, and no intense hurricanes.

June outlook
My outlook for the first two weeks of June was posted earlier today.

Radio play
National Public Radio's The Story program will be airing a long interview with me today about my flight into Hurricane Hugo in 1989. The show is carried on NPR stations in MI, WI, IL, IN, IA, MN, NC, NY, VA, and WI, and airs live today at 1pm or 8pm EDT. Check http://thestory.org/Stations for local stations and times. You can also listen live on the Internet at NPR station wunc.org in North Carolina. The host, Dick Gordon, is a very gifted interviewer, and it should be an interesting program. The MP3 of the interview is at http://thestory.org/archive/the_story_263_Hunting_Hurricanes.mp3.


Last night, I was guest on the Barometer Bob Show. You can listen to a podcast of my 50-minute spiel at http://www.barometerbobshow.com/podcast/.

Jeff Masters

Gulf of Mexico disturbance and the June hurricane outlook

By: JeffMasters, 4:52 PM GMT on June 01, 2007

A large area of disturbed weather continues over the Western Caribbean and Gulf of Mexico in association with a non-tropical area of low pressure. There is no circulation evident on QuikSCAT, satellite loops, or the Tampa Bay radar. Wind shear is about 20-40 knots, which is unfavorable for tropical storm formation. The shear is expected to remain high over the storm for the next few days, and I don't expect it to develop into a tropical depression. However, the storm has a lot of tropical moisture with it, and it should bring rains of 1-3 inches over western Cuba and much of Florida over the next two days, as well as the threat of 50 mph wind gusts and a few weak tornadoes. A Hurricane Hunter aircraft is scheduled to investigate the system at 2pm EDT today.


Figure 1. Total rainfall from the Key West radar.

June outlook
June is typically the quietest month of the Atlantic hurricane season. The basin averages 0.5 named storms in June. Only one major hurricane has made landfall in June--Category 4 Hurricane Audrey of 1957, which struck the Texas/Louisiana border area on June 27 of that year, killing 550. The highest number of named storms for the month is three, which occurred in 1936 and 1968. In the 12 years since the current active hurricane period began in 1995, there have been nine June named storms. Four tropical storms have formed in the first half of June in that 12-year period, giving a historical 33% chance of a first-half-of-June named storm.


Figure 1. Tracks of all June tropical storms and hurricanes since 1851.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) are still quite cool in June, which limits the regions where tropical storm formation can occur. Typically, June storms only form over the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida, where water temperatures are warmest (Figure 1). This year (Figure 2), SSTs are below average in the region surrounding Florida, so we should expect any storms that do form to occur in the Western Gulf of Mexico or Western Caribbean. June storms typically form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance. African tropical waves, which serve as the instigators of about 85% of all major hurricanes, are usually too far south in June to trigger tropical storm formation. Every so often, a tropical wave coming off the coast of Africa moves far enough north to act as a seed for a June tropical storm. Another possibility is that the disturbed weather area in the Eastern Pacific Intertropical Convergence Zone (ITCZ) will push north into the Western Caribbean and spawn a storm there. This was the case for last year's Tropical Storm Alberto (which may have also had help from an African wave).


Figure 2. Sea Surface Temperature (SST) departure from average for May 31, 2007.

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 3) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. As we can see, there is much less heat energy available this year than in 2005, which recorded the highest SSTs ever measured in the tropical Atlantic. I expect that the TCHP will continue to remain below 2005 levels this year, so we should not see as many intense hurricane as we saw in 2005.


Figure 3. Tropical Cyclone Heat Potential (TCHP) for May 31 2005 (top) and May 31 2007 (bottom). TCHP is a measure of the total heat energy available in the ocean. Record high values of TCHP were observed in 2005. TCHP this year is much lower. Image credit: NOAA/AOML.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart.

Wind shear over the past 11 days (Figure 4) has been very high over North America and the surrounding waters of the Gulf of Mexico and Atlantic. This is very typical for June, when the jet stream is still very active and quite far south. The jet stream will gradually weaken and retreat northwards as summer progresses, bringing lower wind shear and greater chances for tropical storm formation. Right now, the Caribbean is the only region with wind shear low enough to support tropical storm formation. The latest two-week forecast from the GFS model predicts that wind shear will remain high over the Gulf of Mexico for the first half of June, and I don't expect and tropical storms to form in the Gulf the next two weeks. Wind shear over the Caribbean is expected to fluctuate between hostile and favorable levels over the next two weeks, so it is possible we could get a tropical storm forming in the Western Caribbean.


Figure 4. Top: Average wind shear over the past 11 days. Wind shear is the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude) in meters per second (multiply by two to get the approximate wind shear in knots). In most circumstances, wind shear above 20 knots (10 m/s, the blue colors in the top image) will act to inhibit tropical storm formation. Wind shear below 12 knots (6 m/s, the orange colors) is very conducive for tropical storm formation.
Bottom: Departure of wind shear from average for the past 11 days in meters per second. Note the higher than average wind shear values over the Gulf of Mexico, a prime breeding ground for June tropical storms.

Dry air and African dust
It's too early to concern ourselves with dry air and dust coming off the coast of Africa, since these dust outbreaks don't make it all the way to the June tropical cyclone breeding grounds in the Western Caribbean and the Gulf of Mexico. Developing storms do have to contend with dry air from Canada moving off the U.S. coast; this was a key reason why this year's Subtropical Storm Andrea never became a tropical storm.

Steering currents
The steering current pattern over the past few weeks has been much like 2006, with an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. These troughs are frequent enough and strong enough to recurve any tropical storms of hurricanes that penetrate north of the Caribbean Sea. Steering current patterns are not predictable more than about two weeks in advance, and there is no telling if we are in for a repeat of the favorable 2006 steering current pattern that recurved every storm out to sea. It is encouraging to note that in 2006 the steering current pattern locked into place in late May and stayed that way for almost the entirety of the hurricane season. I am hopeful that this pattern will occur again this year, but there is no way of telling at this point.

Summary
Recent history suggests a 33% chance of a named storm occurring in the first half of June. Given the current SST pattern and two-week wind shear forecast, the Western Caribbean is the most likely area for a storm to occur. Any storm forming in this region would likely move north or northeastward, impacting Cuba, Florida, and the Bahamas. Due to the high levels of wind shear expected over the next two weeks, I'm forecasting only a 20% chance of a named storm forming during this period.

Radio play
National Public Radio's The Story program will be airing a long interview with me today about my flight into Hurricane Hugo in 1989. The show is carried on NPR stations in MI, WI, IL, IN, IA, MN, NC, NY, VA, and WI, and airs live today at 1pm or 8pm EDT. Check http://thestory.org/Stations for local stations and times. You can also listen live on the Internet at NPR station wunc.org in North Carolina. The host, Dick Gordon, is a very gifted interviewer, and it should be an interesting program.

Last night, I was guest on the Barometer Bob Show. You can listen to a podcast of my 50-minute spiel at http://www.barometerbobshow.com/podcast/.

Jeff Masters

Needed rains headed for Florida

By: JeffMasters, 1:58 PM GMT on June 01, 2007

A large area of disturbed weather continues over the Western Caribbean and Gulf of Mexico in association with a non-tropical area of low pressure. There is no circulation evident on QuikSCAT or satellite loops, and wind shear is about 20-30 knots, which is unfavorable for tropical storm formation. Wind shear is expected to remain high over the storm for the next few days, and I don't expect it to develop into a tropical depression. However, the storm has a lot of tropical moisture with it, and it should bring rains of 1-3 inches over western Cuba and much of Florida over the next two days, as well as the threat of 50 mph wind gusts and a few weak tornadoes. A Hurricane Hunter aircraft was scheduled to investigate the system at 2pm EDT today, but I expect this will get canceled.


Figure 1. Total rainfall from the Key West radar.

June outlook
I'll be posting my forecast for the first two weeks of June by 1pm EDT today. I plan to offer 2-week hurricane activity forecasts on the 1st and 16th of each month (except August 1, when I'll be on vacation). These forecasts will have the probability of hurricane formation for the coming two weeks, where the hurricanes will go if they form due to the prevailing steering currents, plus a look at how sea surface temperatures, wind shear, the trade winds, and dry air coming off of Africa are affecting hurricane formation in the Atlantic.

Radio play
National Public Radio's The Story program will be airing a long interview with me today about my flight into Hurricane Hugo in 1989. The show is carried on NPR stations in MI, WI, IL, IN, IA, MN, NC, NY, VA, and WI, and airs live today at 1pm or 8pm EDT. Check http://thestory.org/Stations for local stations and times. You can also listen live on the Internet at NPR station wunc.org in North Carolina. The host, Dick Gordon, is a very gifted interviewer, and it should be an interesting program.

Last night, I was guest on the Barometer Bob Show. You can listen to a podcast of my 50-minute spiel at http://www.barometerbobshow.com/podcast/.

Jeff Masters


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

Category 6™

About

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