Category 6™

Air pollution season begins; new hurricane buoys go on-line

By: JeffMasters, 2:35 PM GMT on April 30, 2007

Air pollution season begins May 1 and lasts through the end of September. The U.S. Environmental Protection Agency (EPA) has designated this week as Air Pollution Awareness Week, so I'll be pointing people to the EPA web site designed for the occasion. We worry most about air pollution in the summer for two reasons:

1) The pollutant of most concern in the U.S. Is ground-level ozone. Ozone is a colorless odorless gas. It's the same kind of gas that's found in the ozone layer. But in the ozone layer, high in the Earth's stratosphere, ozone protects us from the sun. At ground level, where we live, ozone pollution is unhealthy to breathe. Ground-level ozone forms when nitrogen oxides and gaseous carbon compounds from cars, trucks, power plants, industries, and some consumer products cook in the sun. Intense sunlight and hot temperatures make the most ozone. Thus, hot summer days in late afternoon have the highest ozone pollution--unless strong winds disperse the foul air.

2) Summertime has the the greatest incidence of multi-day periods with clear weather and light winds. These "air stagnation episodes" allow pollutants to build up, since there is little wind to disperse the stuff. Air stagnation episodes are much less common during other times of year, when low pressure systems and their attached cold fronts and warm fronts bring strong winds that keep pollution levels lower.

I'll have a new blog Tuesday or Wednesday, and take a look at last year's pollution season. Is air quality improving in the U.S.?

Figure 1. Map of hurricane buoys maintained by the National Data Buoy Center. Image credit: NOAA.

New hurricane buoys on-line
Two new ocean buoys are now on-line to help monitor hurricanes, thanks to over $2 million in special hurricane funding approved by Congress in the wake of the Hurricane Katrina disaster in 2005. Buoy 42059, a few hundred miles south of Puerto Rico, and buoy 41043, a few hundred miles north of Puerto Rico, are strategically placed to offer data in area where hurricanes frequently traverse. Six more buoys are scheduled to come on-line in the next year, and these will be a big help in tracking hurricanes.

Jeff Masters

Air and Water Pollution

Weather radios now required for Indiana mobile homes

By: JeffMasters, 1:36 PM GMT on April 27, 2007

Mobile homes sold in the state of Indiana after June 30 this year must come equipped with a weather radio capable of alerting residents of an approaching tornado, thanks to a law signed by Indiana governor Mitch Daniels this week. The legislation, dubbed "C.J.'s Law", was named after 2-year old C.J. Martin, who died in a F3 tornado that killed 25 people in southwestern Indiana on November 6, 2005. Twenty of the victims lived in the Eastbrook Mobile Home Park in Evansville. The storm hit at 2am, when many residents were asleep and didn't hear the tornado sirens. C.J.'s mother, Kathryn Martin, pushed lawmakers to adopt the bill, pointing out that weather radios with a tone alert system could have saved many lives in the mobile home park.

This type of law makes great sense for mobile homes sold in tornado alley--think of it as a companion to your smoke detector in the house. Mobile home residents make up just 7% of the U.S. population, but account for 40% of the deaths in tornadoes. However, there are a number of issues that may make the law ineffective. Firstly, what type of weather radio will be purchased? There are many poor quality units out there, prone to radio interference, and difficult to program (weather radios require the user to input a special SAME code, needed to issue tone alerts when a tornado warning is issued). Secondly, the NWS sends out weekly or monthly test alerts on weather radio--how many mobile home owners will simply turn off their weather radios because they are sick of hearing the regular tests? Or turn them off after a few false alarms wake them up in the middle of the night for tornadoes that appear on Doppler radar, but never touch down? Thirdly, once the residents of a mobile home park are awakened by an alert, where do they go? Indiana, like most states, has no law requiring mobile home parks to have a tornado shelter. However, there is now Federal money available for mobile home parks to construct tornado shelters, so the number of parks with shelters may increase in coming years. In summary, the law has the potential to save lives--but only if it is properly enacted.

Figure 1. Damage to C.J. Martin's mobile home park near Evansville, Indiana due to the November 6, 2005 tornado. Image credit: Paducah, KY NWS.

Jeff Masters


Killer tornado hits Texas and Mexico

By: JeffMasters, 2:14 PM GMT on April 25, 2007

A killer tornado swept through Piedras Negras, Mexico, crossed the Rio Grande River, and brought devastation to the small town of Eagle Pass, Texas, at about 7pm CDT last night. The tornado killed three and injured 87 in Mexico; seven died in Texas, and 74 were injured. Five of the U.S. deaths occurred in a single mobile home when it was picked up and tossed into an elementary school. The tornado destroyed 20 homes, two schools, and the local sewage treatment plant in Eagle Pass. Killer tornadoes in Mexico are rare, as most of the country is too far south to get tornado weather, and is sparsely populated in the Texas border regions that are prone to tornadoes. Mexico's worst tornado that I could find record of occurred in 2004, when a tornado killed 32 in Piedras Negras.

Tornadoes were also reported last night in Oklahoma, Kansas, and eastern Colorado. More tornadoes are possible today, as the Storm Prediction Center (SPC) has placed much of the Mississippi Valley under it's "Slight Risk" area. This is a major step down from yesterday's risk level, though, when SPC had portions of Texas under its "High Risk" area (although Eagle Pass was in the "Moderate Risk" area). This is the third time in 2007 that SPC issued a "High Risk" forecast. A "High Risk" forecast was also issued for the EF4 March 1 Enterprise, Alabama tornado that killed 20. It's been a bad year for tornadoes--last night's storm brought the 2007 U.S. death toll to 59. The average tornado death toll for the entire year has been just 46 the past three years. It's only April, and we still have the peak tornado months of May and June to get through.

Figure 1. Radar reflectivity image of the April 24, 2007 tornado as it approached Eagle Pass, Texas. Note the distinctive hook shape of the radar echo, which is characteristic of supercell thunderstorms that spawn strong tornadoes.

Figure 2. Radar velocity image of the April 24, 2007 tornado as it approached Eagle Pass, Texas. Note the area of blue and red echoes just south of the circle with a "+" inside it that marks the location of Eagle Pass. The blues and reds show that strong winds going both towards and away from the radar exist in a small area, denoting the presence of a parent mesocyclone (rotating thunderstorm) and a tornado.

Figure 3. Vertically integrated Liquid Water (VIL), in kilograms per square meter, for the April 24, 2007 tornado as it approached Eagle Pass, Texas. VIL is a measure of how much water is in the storm, when measured from the surface to the top of the storm. The Eagle Pass thunderstorm had cloud tops at 56,000 feet, so a column of air one meter square extending from the surface to 56,000 feet had up to 70 kilograms of liquid water in it. That's a lot of water available for hailstones to grow in, and large hail up to 1.75 inches in diameter was observed with this storm. A VIL of at least 50 is typically required to get large hail two inches in diameter in April in the Plains. A VIL of about 65 is needed later in summer, when the thunderstorms grow taller and more liquid water is needed to make large hail. See the Oklahoma Climatological Survey VIL help page for more information.

We've saved a 300 Mb radar animation of the Eagle Pass tornado for those interested.

Jeff Masters


Big Wind in the Windy City

By: JeffMasters, 2:30 PM GMT on April 24, 2007

Tornadoes hit the Plains again last night, and several people in rural Nebraska were injured when a tornado ripped through farmland in the western part of the state. The Storm Prediction Center has put a large area of the Plains under their Moderate Risk region for severe weather today. Wunderphotographer Mike Theiss chased the tornado that caused severe damage in Tulia, Texas over the weekend, and will be out chasing storms in the Plains today. Mike will be chasing frequently over the coming month, so be sure to tune into his blog for the latest!

Big wind in the Windy City
What would happen if a violent, long-track EF4 or EF5 tornado ripped through a densely populated urban area like Chicago? That was the question posed by tornado researcher Josh Wurman of the Center for Severe Weather Research in Boulder and three co-authors in a paper published in the January 2007 issue of the Bulletin of the American Meteorological Society. Their astonishing answer: damage of $40 billion and 13,000-45,000 people killed--the deadliest natural disaster in American history.

A tornado death toll in the ten of thousands seems outlandish when one considers past history. After all, the deadliest tornado in U.S. history--the great Tri-state Tornado of March 18, 1925--killed 695 people in its deadly rampage across rural Missouri, Illinois, and Indiana. That was before the advent of Doppler radar and the National Weather Service's excellent tornado warning system. In fact, there has not been a tornado death toll over 100 since 1953, the year the NWS began issuing tornado warnings. Chicago has been hit by one violent tornado. On April 21, 1967 a 200-yard wide F4 tornado formed in Palos Hills in Cook County, and tore a 16-miles long trail of destruction through Oak Lawn and the south side of Chicago. Thirty-three people died, 500 more were injured, and damage was estimated at $50 million.

The paper by Wurman et al., "Low-level winds in tornadoes and the potential catastrophic tornado impacts in urban areas" opens with an analysis of the wind structure of two F5 tornadoes captured on mobile "Doppler on Wheels" radar systems--the May 3, 1999 Bridgecreek-Moore tornado, which hit the southern suburbs of Oklahoma City, and the Mulhall, Oklahoma tornado of the same day, which moved over sparsely populated rural regions. The Bridgecreek-Moore tornado had the highest winds ever measured in a tornado, 302 mph. Winds of EF4 to EF5 strength (greater than 170 mph) are capable of completely destroying a typical home, and occurred over a 350 meter (1150 foot) wide swath along this tornado's path. The Mulhall tornado had weaker winds topping out at 245-255 mph, but had EF4 to EF5 winds over a much wider swath--1600 meters (one mile).

The F4 to F5 winds of the Bridgecreek-Moore tornado killed 36 people. Given the population of the area hit, between 1% and 3% of the people exposed to these winds died. The authors thought that this number was unusually low, given the excellent warnings and high degree of tornado awareness in Oklahoma's population. They cited the death rate in the 1998 Spencer, South Dakota F4 tornado that destroyed 30 structures and caused six deaths, resulting in a death rate of 6% (assuming 3.3 people lived in each structure). There are no studies that relate the probability of death to the amount of damage a structure receives, and the authors estimated crudely that the death rate per totally destroyed structure is 10%. This number will go down sharply if there is a long warning time, as there was in the Oklahoma tornadoes. If one takes the Mulhall tornado's track and superimposes it on a densely populated region of Chicago (Figure 1), one sees that a much higher number of buildings are impacted due to the density of houses. Many of these are high-rise apartment buildings that would not be totally destroyed, and the authors assume a 1% death rate in these structures. Assuming a 1% death rate in the partially destroyed high-rise apartment buildings and a 10% death rate in the homes totally destroyed along the simulated tornado's path, one arrives at a figure of 13,000-45,000 killed in Chicago by a violent, long-track tornado. The math can applied to other cities, as well, resulting in deaths tolls as high as 14,000 in St. Louis, 22,000 in Dallas, 17,000 in Houston, 15,000 in Atlanta, and 8,000 in Oklahoma City.

Figure 1. Wind speed swaths for the 1999 F5 Mulhall, Oklahoma tornado if it were to traverse a densely populated area of Chicago. Units are in meters/sec (120 m/s = 269 mph, 102 m/s = 228 mph, and 76 m/s = 170 mph). Winds above 170 mph usually completely destroy an average house, with a crudely estimated fatality rate of 10%, according to Wurman et al.. Insets x, y, and z refer to satellite photo insets in Figure 2. Image credit: Bulletin of the American Meteorological Society.

Figure 2. Aerial photographs from Google Earth of densely populated area of Chicago (insets x, y, and z from Figure 1) These areas contain mainly single-family homes, with housing units densely packed on small lots. A mixture of three-story apartments and single-family homes is typical across the Chicago metropolitan area and many older cities such as New York City and Detroit. At lower right is a photo of Moore, OK, showing lower density housing like the 1999 Bridgecreek-Moore tornado passed through.

How realistic are these estimates? Could a violent tornado really eclipse the Galveston Hurricane (8,000 killed) as this nation's worst natural disaster? The authors admit that their method of estimating deaths is crude, and considered death rates from only two storms to arrive at their estimates. I took a look at the fatalities from some other F5 tornadoes since 1991, and the death rates are highly variable (3% for the 1000 buildings destroyed by the 1998 Birmingham, AL tornado; 66% for the 41 buildings destroyed by the 1997 Jarrell, Texas tornado; 0% for the 66 buildings destroyed in the 1996 Oakfield, Wisconsin tornado; and 5% for the 350 buildings destroyed in the 1991 Andover, Kansas tornado). Based on these numbers, a 5% death rate may be more typical than the 10% death rate assumed in the Wurman et al. study. Violent tornadoes have hit downtown areas in the past, but have not affected nearly the number of structures as considered in the Wurman et al. study. The authors emphasize that even if their death rate estimates are off by a factor ten, a violent tornado in Chicago could still kill 1,300-4,500 people. The authors don't give an expected frequency for such an event, but I speculate that a violent tornado capable of killing thousands will probably occur in a major U.S. city once every few hundred years--or perhaps as long as 1000 years, considering that there have not been any F5 tornadoes in the U.S. since 1999.

Figure 3. Tornadoes to affect the Chicago area, 1950-2005. Background image credit: Google Earth. Tornado paths: Dr. Perry Samson.

Jeff Masters


Earth Day photos; severe weather outbreak in the Plains this week

By: JeffMasters, 4:18 PM GMT on April 22, 2007

On Earth Day, I like to post a blog celebrating the beauty and diversity of Earth's amazing atmosphere, by featuring some of my favorite wunderphotos posted during the year. This year, my favorite photo was posted by Gary Blevins (Photo5150), who posted "Fire Tornado". The intense heat generated by this forest fire in California formed a strong updraft, and air flowing in from the sides to replace the air sucked out by the updraft created a swirling dust-devil-like "fire tornado". Thanks to all of you who shared your weather experiences through wunderphotos and blogs over the past year! The community of weather appreciators that has emerged here at has been an unexpected and wonderful thing to tune into each day.

And truffula trees are what everyone needs.
Plant a new truffula -- treat it with care.
Give it clean water and feed it fresh air.
Grow a forest -- protect it from axes that hack.
Then the Lorax and all of his friends may come back!

--From Dr. Suess' The Lorax

I've linked in a few more of my favorite wunderphotos below. I'll be back with a new blog Tuesday.

Severe weather in the Plains
Tornadoes hit the Texas Panhandle over the weekend, and the Storm Prediction Center has put portions of Texas, Oklahoma, Kansas, and Colorado under their Moderate Risk region for severe weather both Monday and Tuesday. Wunderphotographer Mike Theiss was there to cover the action Sunday, and saw the tornado that caused severe damage in Tulia, Texas. He will be in the Plains chasing tornadoes this week, so be sure to tune into his blog for the latest!

--Jeff Masters

Atmospheric Phenomena

2007 Atlantic Hurricane Season Outlook

By: JeffMasters, 4:24 PM GMT on April 19, 2007

It's too soon to find many clues about what the upcoming hurricane season might be like, since we are facing the famed "April Predictability Barrier". The atmosphere is not predictable enough to make a skillful forecast of seasonal hurricane activity in April (this changes by late May, when skillful predictions of the upcoming hurricane season CAN be made). Thus, we should put little faith in the predictions by the Klotzback/Gray group and TSR made in April, calling for 17 named storms, 9 hurricanes, and 4 or 5 intense hurricanes. However, there are a few indicators we can start looking at. I covered these in a talk I gave last week at Eckerd College in St. Petersburg that many of you asked to hear about, so here goes!

Figure 1. Sea Surface Temperature (SST) difference between March 2007 and 2005. Cool colors are regions where the SST was colder in 2007, and yellows and greens where SSTs were warmer in 2007. Image credit: NOAA/ESRL.

Sea Surface Temperature (SST) Outlook
Sea Surface temperatures are at the heart of any attempt to analyze seasonal hurricane activity, since SSTs change slowly and have a major impact on both the number of storms that form and their intensity. For example, the record-breaking Hurricane Season of 2005 had the warmest SSTs ever observed in the tropical Atlantic. Comparing the SSTs in March of 2007 with March of 2005 (Figure 1), we see that SSTs were more than 1 degree C cooler in 2007 over a large portion of the Atlantic west of the Lesser Antilles Islands. This is a key portion of the "Main Development Region" (MDR) for hurricanes (red box in Figure 1). The MDR is where 85% of all major hurricane form. Note, though, that the regions where Katrina, Rita, and Wilma formed--the Bahamas to the Western Caribbean--have SSTs warmer this year than in 2005. Overall, SSTs are well above average across most of the tropical Atlantic this year, continuing the pattern we have seen since 1995, when the current active Atlantic hurricane period began. We can expect this year's SSTs to support a more active than usual hurricane season, although there is still time for a significant cooling to occur if we get a major increase in the speed of the trade winds over the next few months.

Figure 2. Sea Surface Temperature (SST) departure from average in the region 120W-170W, 5S-5N (called the Nio 3.4 region) for 2006 and 2007. Temperatures +0.5C above average in this region indicate an El Nio episode; temperatures -0.5C below average indicate an La Nia. Note that EL Nio peaked in December, then rapidly decayed to neutral conditions in early February. Image credit:NOAA Climate Prediction Center.

El Nio/La Nia Outlook
Obviously, SSTs don't tell the whole story, since the second highest SSTs in the tropical Atlantic since the 1870s occurred last year. To our great relief, we had a very normal year with 10 named storms, 5 hurricanes, and 2 intense hurricanes. As we see in Figure 2, that was in part because 2006 was an El Nio year. El Nio events usually suppress Atlantic hurricane activity, by bringing increased wind shear and dryer, sinking air over the Atlantic. This is not always the case--recall 2004? El Nio conditions were even stronger that year (as measured by SST departures from average in the Equatorial Pacific), yet that year saw 15 named storms, 9 hurricanes, and 6 intense hurricanes in the Atlantic. Florida got walloped with four hurricanes.

Figure 3. Sea Surface Temperature (SST) departure from average (left) and wind shear departure from average (right) from the April 10, 2007 run of NOAA's CFS model. The forecasts are for the 3-month period August-October spanning the most active part of hurricane season. Note the long tongue of cooler than average waters forecast to extend from the South American coast along the Equatorial Pacific--the telltale sign of a La Nia episode. Image credit:NOAA Climate Prediction Center.

Regardless, El Nio is gone this year, and SSTs have been nearly average across the Equatorial Pacific since mid-February. Is El Nio likely to come back, or will its evil twin, La Nia strike this year? Well, according the early April run of NOAA's Climate Forecast System (CFS) model (Figure 3), we can expect a weak to moderate La Nia event during hurricane season (August-October). This should bring below average values of wind shear over the Atlantic, which should enhance hurricane activity. Other forecast models predict neutral conditions for hurricane season, and very few models foresee a return to El Nio conditions this year. NOAA's April 5 El Nio discussion indicates that the current pattern of ocean temperatures observed over the Equatorial Pacific is consistent with a developing La Nia event. The International Research Institute for Climate and Society is forecasting only a 10% chance of El Nio conditions during hurricane season in 2007. The chances of La Nia are put at 50%, and 40% for neutral conditions. What is the skill of these forecasts in April for an upcoming hurricane season? IRI doesn't tell us, but it's not good. Last year's April forecasts failed to predict the arrival of El Nio during hurricane season, leading to a large overestimation of hurricane activity. Still, the best information we have at this time says that El Nio is unlikely to occur during hurricane season, Since the active period of hurricane activity that we are in began in 1995, both La Nia and neutral years have seen very high levels of hurricane activity (Figure 4). In fact, calling La Nia an "evil twin" is not fair, since neutral years have had even higher hurricane activity than La Nia years (thanks in great measure to the Hurricane Season of 2005).

Figure 4. Observed numbers of named storms, hurricanes, and intense hurricanes (Category 3 and higher) for the 12-year period beginning in 1995. Background image is of Australia's Tropical Cyclone Monica, the most intense storm of 2006.

African dust outlook
African dust is thought to suppress Atlantic hurricane activity, although its role is not well understood. As I explained in a blog last year, research shows that the presence of drought conditions in the Sahel region of Africa the previous year will increase the amount of dust wafting over the Atlantic during hurricane season. This occurs because drought-damaged soil takes about a year to dry up and create lots of dust to be blown away. Last year saw average to above-average rains during the rainy season (June-September) over the Sahel (Figure 5). This was also the case in 2005, so in theory, two straight years of good rains in the Sahel should act to keep African dust levels over the Atlantic no higher than average this hurricane season. The last significant drought years in the Sahel were 2001 and 2002.

Figure 5. Departure of precipitation from average in Africa for August 2006. The region in the red box is the Sahel region of Africa that accounts for most of the year-to-year variability in dust transport over the Atlantic Ocean. Image credit: NOAA Climate Prediction Center.

The outlook for the 2007 Atlantic hurricane season
If the forecasts of above normal sea surface temperatures, no El Nio, and below average African dust come true, the 2007 Atlantic hurricane season should be very active. However, since our skill in predicting these things in April is low, the most reasonable forecast to make is a post-1995 climatology forecast: 15 named storms, 8 hurricanes, and 4 intense hurricanes. (The 100-year climatology is 10 named storms, 6 hurricanes, and 2 intense hurricanes). By May, the atmosphere and ocean begin to give us significant clues about the upcoming hurricane season. Tune into the late May seasonal forecasts issued by NOAA, the Klotzback/Gray group, TSR, and Cuba's meteorological service!

My next blog will be Earth Day--Sunday, April 22. Next week, I also plan to review an article published today that hypothesizes that global warming should cause a significant increase in wind shear over the Atlantic and Eastern Pacific, inhibiting hurricanes.

Jeff Masters

Nor'easter of 2007 winds down

By: JeffMasters, 1:50 PM GMT on April 17, 2007

The Nor'easter of 2007 is steadily winding down, but will continue to bring high winds, minor coastal flooding, and up to one inch of rain to portions of the Northeast U.S. today. The nor'easter brought the heaviest rains since 1882 to New York City and northern New Jersey, triggering widespread flooding that will cost hundreds of millions of dollars. Hoboken, NJ became an island when roads surrounding the city flooded up to three feet deep, submerging cars, basements and parking lots. Over 1400 people were evacuated from homes along the Raritan River in New Jersey, which crested 10.5 feet above flood stage. At least 5000 people were evacuated in New Hampshire due to flooding, and over 400 roads closed. A woman and her 4-year-old granddaughter died when they were swept into fast-moving floodwaters as they tried to cross a washed-out section of a road in Lebanon, Maine, near the New Hampshire border. Winds gusting to 60 mph knocked out power to over 123,000 homes in Maine, the second largest power outage in state history. The record was set during an ice storm in 1998 that knocked out power to 340,000 homes.

Storm surges
Along the Massachusetts coast, tidal flooding has been minor to moderate, with overwash and erosion of dunes, flooding of coastal roads and some homes, but minimal damage to buildings. The peak storm surge in Boston at high tide was 2.2 feet yesterday, which added to the regular high tide to bring a 13.2 foot storm tide. Tonight's high tide may bring a storm tide half a foot higher, leading to moderate flooding. The new moon will bring a slightly higher high tide tonight than yesterday, and winds will remain gale-force, pushing 20-foot waves against the coast. Maine has already seen its highest storm surge from the storm--2.5-3.5 feet of surge during high tide yesterday. This was the fourth highest storm surge along the Maine coast since 1990. Storm surges of 1.5-2 feet are likely along the Maine coast during today's high tide cycles. Storm surges of 1-2 feet are likely at high tide today in New York City and Long Island Sound, which will cause additional minor to moderate flooding. The storm caused major erosion at Jones Beach, Robert Moses State Park and beaches in Montauk on Long Island.

Winds and snow
Tupper Lake, NY recorded 26 inches of snow. Winds gusts of 72 mph were observed in Milton, MA; 81 mph in Cape Elizabeth, ME, and 156 mph at Mount Washington in New Hampshire.

Figure 1. Visible image of the 2007 Nor'easter on Monday at 4 pm EDT. Image credit: The University of Wisconsin CIMSS Satellite Blog, which has a nice page of images and animations of the Nor'easter of 2007.

I'll have a new blog Wednesday or Thursday.
Jeff Masters


Nor'easter of 2007 slowly winds down

By: JeffMasters, 9:25 PM GMT on April 16, 2007

The Nor'easter of 2007 peaked in intensity at 8am EDT today with a central pressure of 967 mb, and has begun a slow decay. At 4pm EDT, the low had weakened to about 979 mb, and was centered over central Long Island. The Nor'easter is forecast to loop across southwest Connecticut and than move south across western Long Island/New York City early this evening as is gradually continues to fill. The worst of the rains and storm surge flooding have already occurred in most areas, but moderate storm surge flooding, freshwater flooding, and high winds will continue to cause problems throughout the Northeast through Tuesday night. A secondary low pressure system is expected to develop Tuesday south of Maine, leading to an increase in winds and storm surge flooding during the high tide cycles on Tuesday along the Massachusetts, New Hampshire, and Maine coasts. Up to 2-3 feet of storm surge flooding is expected along the Massachusetts coast during high tide Tuesday night.

The highest winds at the coast from the storm were 67 mph gusting to 80mph at 2pm EDT on the Maine coast at Matinicus Rock. The highest winds on top of New Hampshire's Mount Washington were 112 mph, gusting to 138, measured at 11am today.

Central Park in New York City recorded 7.57 inches of rain yesterday, the most ever from a Nor'easter, and their second highest daily rainfall ever measured. The record was set on September 23rd 1882, when 8.28 inches fell during a slow-moving tropical storm. Rainfall had totalled 8.31 inches at Central Park by 9am today. Rivervale, NJ has had the most rain I could find thus far--9.3 inches.

Figure 1. Total precipitation estimated by radar for the Nor'easter of 2007.

River flooding
All-time record flood levels were recorded or are expected on the Ramapo, Rockaway, and Passaic Rivers in New Jersey. Many rivers were 4-5 feet above flood stage in New Jersey today.

Coastal flooding
A 4-5 foot surge along the western shores of Long Island Sound was the highest from the storm. Wave heights up to 29 feet were measured in Massachusetts Bay.

Up to 17 inches of new snow fell in the White Mountains of New Hampshire.

I'll post an update on the Nor'easter on Tuesday. My condolences to all those affected by the tragedy today at Virginia Tech, and by today's storm.

Jeff Masters

Winter Weather

Nor'easter of 2007 peaks in intensity, continues pounding New England

By: JeffMasters, 1:49 PM GMT on April 16, 2007

The Nor'easter of 2007 continues to pound the Northeast U.S. today with flooding rains, high winds, and severe coastal storm surges. The storm peaked in intensity at about 8am EDT with a central pressure of 967 mb--a pressure similar to what one finds in a Category 2 hurricane. However, the nor'easter is not as tightly wound as a hurricane, and the highest winds were were 61 mph gusting to 70mph at 8am EDT on the Maine coast at Matinicus Rock. Winds were 60 mph gusting to 64 mph at the Isle of Shoals C-MAN station on the coast of New Hampshire at 7am EDT this morning.

Huge rains in New York and New Jersey
Central Park in New York City recorded 7.57 inches of rain yesterday, the most ever from a Nor'easter, and their second highest daily rainfall ever measured. The record was set on September 23rd 1882, when 8.28 inches fell during a slow-moving tropical storm. Rainfall total of 5-9 inches were common over much of New Jersey and the New York City area over the past 36 hours (Figure 1), bringing the worst flooding since Tropical Storm Floyd in 1999. Rivervale, NJ has had the most rain I could find thus far--9.3 inches.

Today's running of the Boston Marathon will be a cold, wet one, as 3-5 inches of rain have already fallen over the area, and another 1-2 inches could fall today. The heaviest rains today will affect coastal New Hampshire and Maine, where 5-8 inches are expected.

Figure 1. Total precipitation estimated by radar for the Nor'easter of 2007.

Coastal flooding
Winds from the 2007 Nor'easter pushed a 2.5 foot storm surge on top of an unusually high "Spring Tide" into the New York City area during this morning's high tide (Figure 2), and a 4-5 foot surge along the western shores of Long Island Sound (Figure 3). The coastal flooding situation may be most serious along the coast north of Boston, where a storm surge of 3-4 feet is occurring during this morning's high tide, and huge waves are battering the coast. Wave heights up to 25 feet were observed just offshore this morning. Coastal flooding is expected all along the Maine and New Hampshire coasts, and downtown Portland, Maine will see water along Commercial Street during high tide today. Waves heights up to 29 feet have been observed this morning off the coast of Maine.

Figure 2. Tidal levels observed at The Battery in New York City.

Figure 2. Tidal levels observed at King's Point in western Long Island Sound on April 15, 2007.

Mount Washington weather
Winds this morning on top of New Hampshire's Mount Washington were 108 mph, gusting to 138. I don't think they'll be painting the railings today! Check out their web site--the current observer comments are particularly interesting!

I'll post an update late this afternoon.
Jeff Masters

Winter Weather

High tide in New York brings flooding

By: JeffMasters, 12:14 AM GMT on April 16, 2007

Winds from the 2007 Nor'easter have pushed a two foot storm surge on top of an unusually high "Spring Tide" into the New York City area at the time of this evening's 7:30pm EDT high tide,(Figure 1). Battering waves on top of the storm surge have undoubtedly caused significant coastal erosion, and possibly damage to some structures along the coast. It could have been worse for New York City, as the peak storm surge of 2.5 feet occurred during the afternoon before high tide. Sustained winds of tropical storm force have been observed most of the day south of Long Island at Ambrose Light, and in Long Island Sound. The situation is worse along the western shores of Long Island Sound, where strong winds have already generated a 3-foot storm surge, which was still increasing in height as of 7:30pm EDT. High tide at King's Point is not until 9:30pm EDT tonight; Long Island Sound may see a destructive 4-foot storm surge at that time (Figure 2).

The Nor'easter is moving slower that expected, and is still centered over North Carolina at 7pm EDT. Central pressure continues to fall rapidly, and is down to 981 mb. The storm is expected to continue to intensify down to 973 mb, and track NNE up the New Jersey coast and over New York City. By 8am EDT Monday, the storm will peak in intensity over Connecticut and stall.

Figure 1. Tidal levels observed at The Battery in New York City as of 7:30pm EDT Sunday April 15. Note that water levels peaked at 2.5 feet above normal during the afternoon, but fell to 2 feet above normal at the time of high tide.

The storm surge from today's storm will rival some of the largest ones ever observed in New York, such as during the "Perfect Storm" of October 31, 1991, and the March 13, 1993 Storm of the Century. The worst coastal flooding in recent years in New York City occurred during the December 11-12 1992 Nor'easter, which damaged as many as 20,000 homes and forced almost 2,000 people to take refuge in emergency storm shelters. Storm surges of 4 feet were recorded near New York City, and 5.5 feet in western Long Island Sound. It is possible that the flooding levels seen in the December 1992 Nor'easter will be exceeded in western Long Island Sound tonight.

Figure 2. Tidal levels observed at King's Point in western Long Island Sound on April 15, 2007.

There is too much other remarkable weather to cover in detail. The entire Northeast coast will see an extended period of storm surge flooding, battering waves, and high winds that will likely cause hundreds of millions of dollars in damage. Heavy rains of over four inches have already fallen at New York's Central Park, a tornado from the storm has caused extensive damage in South Carolina that killed one person, and near blizzard conditions are affecting some mountainous regions of New England.

Mount Washington weather
It's a night to hunker down and stay inside at the Mount Washington observatory in New Hampshire. Winds at 8pm EDT were sustained at 70 mph, gusting to 77, and steadily rising. Keep an eye on the history page for Mount Washington to follow the remarkable weather conditions there.

I'll edit this blog tonight to update the water levels and winds, and have a full new blog Monday morning, and there will also be a separate update on the East Coast Winter Storm blog.

Jeff Masters

Winter Weather

Wind, waters rising across the Northeast

By: JeffMasters, 3:46 PM GMT on April 15, 2007

Water levels are starting to rise along the Atlantic coast from New Jersey to Maine, as the Nor'easter of 2007 prepares to enter its explosive deepening phase. At 2pm EDT, the center of the storm was over North Carolina, with a central pressure of 987 mb. Winds over the ocean are starting to rise significantly. Sustained winds of tropical storm force--44 mph, gusting to 50--were observed at 2pm EDT just south of Long Island at Ambrose Light. The storm is expected to move northeastward and cross out to sea off the Delaware coast this evening, and rapidly intensify to a central pressure of 975 mb as it tracks up the coast of New Jersey and passes directly over New York City.

Figure 1. Tidal levels observed at The Battery in New York City as of 2pm EDT Sunday April 15. Note that water levels were two feet above normal at the time, but it was low tide. High tide tonight (near 00 GMT, or 8pm EDT) will see significant coastal flooding. The Battery is located on the southern tip of Manhattan Island. Image credit:NOAA Tides and Currents website.

Water levels at The Battery in New York City were two feet above normal at 2pm, but coastal flooding had not yet occurred, since it was low tide. The tidal range at New York City is six feet today, and some of the highest tides of the year are expected tonight and Monday, due to the arrival of the new moon. When the Sun, Earth, and Moon all line up (which happens during each new moon and full moon), the highest high tides of the year occur. The strongest winds of the 2007 Nor'easter will affect New York City during high tide tonight at 7:30pm. The expected 3-4 foot storm surge in western Long Island Sound near New York City would match the levels seen there in the "Perfect Storm" of October 31, 1991 (Figure 2), and the March 13, 1993 Storm of the Century. The worst coastal flooding in recent years in New York City occurred during the December 11-12 1992 Nor'easter, which damaged as many as 20,000 homes and forced almost 2,000 people to take refuge in emergency storm shelters. Storm surges of 4 feet were recorded near New York City (Figure 3), and 5.5 feet in western Long Island Sound. Some computer models are forecasting a 4-6 foot storm surge over Long Island Sound tonight, and it is possible that the flooding levels seen in the December 1992 Nor'easter will be exceeded. The timing of the peak of this surge with the high tide cycle will be critical, as will the exact track of the storm. If the storm does track directly over New York City tonight, the relatively calm winds near the center may allow some of the storm surge to flow out of Long Island Sound.

Figure 2. Tidal levels observed at The Battery in New York City during the "Perfect Storm" of October 31, 1991. This storm brought the second highest storm surge to New York City observed in recent years.

Figure 3. Tidal levels observed at The Battery in New York City during the Nor'easter of December 11-12, 1992. This storm brought the highest storm surge to New York City observed since tidal record began at The Battery in 1966.

The same storm also brought heavy snow to Kansas and baseball-sized hail to Texas Saturday, and more severe weather is occurring today across the region where the cold front is passing. However, the main story of this storm will be coastal flooding in the Northeast, and wind damage from tropical-storm force winds. Freshwater flooding from the storm's 3-5 inches of rain could also cause localized flooding problems.

Tune in tonight, I'll have an update, and there will also be a separate update on the East Coast Winter Storm blog.

Jeff Masters

Winter Weather

Hurricane-like Nor'easter may form Sunday

By: JeffMasters, 2:34 PM GMT on April 12, 2007

A major spring Nor'easter with the capability of causing damage equivalent to a Category 1 hurricane may develop Sunday off the U.S. East Coast. A storm system currently crossing the Pacific coast near British Columbia is expected to dive southeastward across the U.S., possibly triggering a significant severe weather outbreak over Texas, Louisiana, and Arkansas on Friday. The storm will emerge into the Atlantic on Sunday near the Virginia Coast and rapidly intensify. By Monday morning, the GFS model is forecasting a 975 mb low pressure system just off the New Jersey coast, with 50-60 mph easterly winds over Long Island Sound and the waters just south of Long Island. The 00Z UKMET model forecasts an even more intense system, similar in strength to a Category 1 hurricane. Other reliable models are less gung-ho. The European model has the storm bottoming out at a pressure of 985 mb, and the NOGAPS model, 982 mb. However, of great concern is the fact that most of the models forecast a very slow moving system that will weaken only gradually, battering the coast for at least three days. This will allow a long period of time for the tropical-storm force winds over the water to pile up high storm surges in Long Island Sound and along the entire Northeast coast from New Jersey to Maine. Combine this with the arrival of one of the highest tides of the year Monday night--the Spring Tide, which occurs at the time of the new moon--and we have the potential for a very serious flooding event. If the worst case scenarios of the models come true, the Tax Day Storm of 2007 could cause extensive moderate to severe coastal flooding, costing hundreds of millions of dollars. The areas at highest risk appear to be New Jersey, New York (especially New York City), Connecticut, Rhode Island, and Massachusetts. Heavy snow is not expected along the coast, but heavy rains may cause flooding problems. As usual, there is considerable uncertainty about the exact track and intensity of the storm, and we'll have a better idea Friday what might be in store for New England. However, I believe there is a greater than 50% chance that this Nor'easter will be strong enough to cause significant storm surge flooding along the New England coast. Damages of at least $100 million are likely.

Figure 1. Forecast from the GFS model for 2am EDT Monday April 16, showing a major Nor'easter off the coast of New England.

My lecture in the Tampa Bay area--location change
I'll be giving a public lecture on Friday, April 13, at Eckerd College in St. Petersburg, Florida. The title of the talk will be, "A Preview of the 2007 Atlantic Hurricane Season--and the Story of a Flight into Hurricane Hugo." The room for the lecture has been changed to Miller Hall (it was Fox Hall). The details:

Friday April 13, 4:00 to 5:00 p.m.
Miller Hall
Eckerd College
4200 54th Avenue S
St. Petersburg, FL 33711
Event information:

Here's a map of where Eckerd College is, and a map of campus. I hope to see some of you there! I'll have time after the talk to chat. You can email me at if you have comments about my appearance.

Tune into the East Coast Winter Weather blog Friday for an update on the 2007 Tax Day Storm. I won't be writing a blog on the storm Friday, but one of the other wunderground meteorologists will. I'll blog on the storm Saturday and/or Sunday if it appears to be a major threat.

Jeff Masters

Winter Weather

Hot, then cold!

By: JeffMasters, 1:49 PM GMT on April 10, 2007

A long and severe cold snap across much of the Eastern U.S. has caused considerable damage to peach and berry crops, canceled numerous baseball games, and brought up to four feet of snow to Michigan's Upper Peninsula. Here in Southeast Michigan, we had our coldest week of April in 25 years, and a new winter storm is likely to bring 2-6 inches of snow on Wednesday. All this wintry weather comes on the heels of the second warmest March in U.S. history. The National Climatic Data Center released statistics showing that March 2007 was 5.6�F (3.1�C) warmer than the 20th century mean of 42.5�F (5.8�C) across the lower 48 states. Only March 1910 was warmer in the 113-year national record. More than 2500 daily record high temperatures were set from the East to the West Coast during the month. On the 13th of March alone more than 250 daily high temperature records were set. The earliest high of 90�F (32�C) occurred in Las Vegas that day and the daily record was broken by 6�F (3.3�C). For the month as a whole more than 200 daily record highs of 90�F or greater occurred in California, Arizona, Texas, Oklahoma, and areas of the Southeast. In contrast, Alaska had its third coldest March ever.

Figure 1. Northern Hemisphere departure of temperature from average for March and the week of April 2-9. Note how the pattern of warmer vs. colder than average temperatures reversed over North America between the two time periods. Images are plotted from the NCAR/NCEP daily reanalysis data, which has interpolation porblems over data-poor areas like the Southern Hemisphere and oceans, so these areas are not plotted. Image credit: NOAA/NCEP.

For the year, the U.S. has had an average January (49th warmest), colder than average February (34th coldest), exceptionally warm March (2nd warmest), and now a very cold April. Climate change science really doesn't have much to say about whether sharp temperature fluctuations like this will become more common in a world undergoing global warming. For now, I'm just attributing the past month's wild swing in temperature to natural variability. The jet stream moved to a completely new pattern between March and early April, reversing where above average and below average temperatures occurred over North America (Figure 1). Where will the jet stream set up for this year's hurricane season, determining the dominant hurricane track? I'll have my first discussion of that in late May, since the jet stream position is generally not predictable more than two weeks in advance.

On Thursday March 8th, the UK TV Channel 4 aired a program titled "The Great Global Warming Swindle". In the words of conservative commentator Thomas Sowell, "Distinguished scientists specializing in climate and climate-related fields talk in plain English and present readily understood graphs showing what a crock the current global warming hysteria is." I've been asked by a number of people to review the movie, but haven't found time to do so. It got yanked from for violating copyright laws, but is available from UK TV Channel 4. The scientists at reviewed the movie, and call it a fraud with distorted, misrepresented, and incorrect science.

My next blog will be Thursday.
Jeff Masters


The Climate Change Storm

By: JeffMasters, 9:14 PM GMT on April 06, 2007

Significant climate change is already occurring, will grow dramatically, and will cause serious disruptions to natural ecosystems and the lives of billions of people world-wide over the coming century. We need to better prepare for the inevitable changes--and attempt to lessen the magnitude of the these changes by reducing greenhouse gas emissions as soon as possible. That's the take-home message from today's latest report from the United Nations-sponsored Intergovernmental Panel on Climate Change (IPCC). Every six years, the IPCC releases a huge, influential study detailing the state of Earth's climate. Part 1 of the 2007 report, summarizing the science of climate change, was released in February. Today's summary, titled "Climate Change Impacts, Adaptation, and Vulnerability" addressed the likely impacts of climate change on Earth's ecosystems and people. Not all of the expected changes will be harmful--the IPCC emphasizes that "impacts of future climate change will be mixed across regions" for temperature rises of 1 to 3 �C above 1990 levels, with the big losers being the poor developing countries. However, if global warming exceeds 2 to 3 �C, the IPCC states it is very likely that all regions of the globe will suffer increased costs or declining benefits. I believe it is the responsibility of every citizen of the planet to take the 30 minutes needed to read the IPCC summary and familiarize themselves with what the world's top scientists say about the likely impacts of climate change. The scope and severity of the Earth-shaking changes that lie ahead present a breathtakingly formidable challenge for humanity.

Figure 1. Locations of significant changes in physical systems (snow, ice and frozen ground, hydrology, coastal processes) and biological systems (land, ocean, and freshwater) from 1970 to 2004. Between 90% and 100% of these changes are consistent with warming global temperatures, due in large part to human-emitted greenhouse gases. White areas are where not enough data existed to determine a temperature change. Figure 1 is a simplified form of Figure SPM-1 of the 2007 IPCC document, "Climate Change Impacts, Adaptation, and Vulnerability--Summary for Policy Makers."

Observed impacts of climate change to date
The IPCC report begins by summarizing observed changes in physical systems (snow, ice and frozen ground, hydrology, coastal processes) and biological systems (land, ocean, and freshwater) reported in 577 papers in the scientific literature between 1990 and 2004 (Figure 1). They conclude, "Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases." Examples for which they are highly (80% chance) or very highly confident (>90% chance) of include:

Earlier bird migrations and leaf unfolding
Poleward shifts in the ranges of various plant and animal species
Shifts in the ranges and numbers of ocean species near the poles
Earlier migrations of fish in rivers
Earlier and increased peaks in spring run-off from glacier- and snow-fed rivers
Warming of lakes and rivers
More and bigger glacial lakes
Melting permafrost

Medium confidence effects (50% chance of being true) observed in the Northern Hemisphere include:

Earlier spring planting of crops
Increases in forest fires and pest damage to forests
Heat-related deaths in Europe, spread of disease in some areas, and changes in allergenic pollen
Hunting and travel by humans over Arctic snow and ice

Future impacts
This is where the IPCC report gets very sobering. Keep in mind that the predicted future impacts may be understated, given the cautious nature of scientists--and the fact that the final version was edited by government officials, who changed the original conclusions of the scientists. I'll present just of few of the more mind-boggling impacts (in blue, with my comments in black), and leave the rest for the interested reader to discover:

The resilience of many ecosystems is likely to be exceeded this century by an unprecedented combination of climate change, associated disturbances (e.g., flooding, drought, wildfire, insects, ocean acidification), and other global change drivers (e.g., land use change, pollution, over-exploitation of resources) (high confidence).
In other words, some ecosystems will collapse, putting the people who depend on these ecosystems in grave peril.
Many millions more people are projected to be flooded every year due to sea-level rise by the 2080s. Those densely-populated and low-lying areas where adaptive capacity is relatively low, and which already face other challenges such as tropical storms or local coastal subsidence, are especially at risk. The numbers affected will be largest in the mega-deltas of Asia and Africa while small islands are especially vulnerable (very high confidence).
Expect damage and human suffering from hurricanes to greatly increase in coming decades, thanks to higher seas levels.
There is medium confidence that at least partial deglaciation of the Greenland ice sheet, and possibly the West Antarctic ice sheet, would occur over a period of time ranging from centuries to millennia for a global average temperature increase of 1-4 �C (relative to 1990-2000), causing a contribution to sea level rise of 4-6 m or more.
Along with drought and ecosystem collapse, sea level rise is my big concern. Sea level before the most recent ice age was about 4-6 meters (13-20 feet) higher than today, at global temperatures that we expect to match by 2100. The IPCC states that a sea level rise of 0.6-1.9 feet (0.18-0.58 meters) is expected by 2100, and a 4-6 meter rise is not likely for centuries. However, our understanding of the response of glaciers to climate warming is poor. An unexpected rapid partial disintegration of the Greenland or West Antarctic ice sheets later this century raising sea levels by 2 meters (6 feet) has at least a 1% chance of occurring, in my opinion.

The language of the 2007 IPCC climate report is couched in uncertainly, but the broad picture is clear: future climate change may rival or exceed a World War in its effect on society. Steps to lessen its impact and adapt to it need to be made as soon as possible. The cost in lives, dollars, and human suffering will be far greater if we do not.

In his 2006 book, The Revenge of Gaia, philosopher-scientist James Lovelock writes, "I am old enough to notice a remarkable similarity between attitudes over sixty years ago towards the threat of war and those now towards the threat of global heating. Most of us think that something unpleasant may soon happen, but we are as confused as we were in 1938 over what form it will take and what to do about it. Our response so far is just like that before the Second World War, and attempt to appease. The Kyoto agreement was uncannily like that of Munich, with politicians out to show they do respond but in reality playing for time...Battle will soon be joined, and what we face now is far more deadly than any blitzkrieg."

The climate change storm is coming, and the wind is already starting to rise.

Next blog
My next blog will be Monday afternoon or Tuesday. I've got several topics in mind--tornadoes in Chicago, Greenland glaciers, or hurricane model improvements.

Jeff Masters

Climate Change

National Hurricane Conference news

By: JeffMasters, 2:58 PM GMT on April 05, 2007

At the National Hurricane Conference in New Orleans this week, scientists from the National Hurricane Center (NHC) took the opportunity to unveil some changes for the upcoming season--and plea for more funding. New NHC chief Bill Proenza repeated his call for a replacement for the aging QuikSCAT satellite, which measures surface winds over ocean areas. Data from this satellite improves hurricane forecasts by 10-16%, he said. Proenza has been vocal about the need for increased funding for hurricane research and operations early in his tenure at NHC, which I welcome wholeheartedly.

New cone of death, new storm surge product
NHC will be modifying the cone of uncertainty that appears around their forecast hurricane tracking maps in 2007. The new cone uses average errors from the past five years of official NHC forecasts. The cone is sized so that storms will fall inside the cone 2/3 of the time, based on these past five years of forecast errors. The old cone simply used the forecast track error averaged over the past ten years of NHC forecasts. The new cone will be about the same size as the old cone for 12-72 hour forecasts, and about 15-25 miles wider beyond that time. will change their track maps to follow the NHC convention.

The NHC also announced that a new experimental "probabilistic storm surge" product will become available this year. The graphic will show the odds that a storm surge of 5, 10 or 15 feet will affect the coast. The forecast comes from NHC's SLOSH storm surge computer model.

Figure 1. Sample of the new Probabilistic Storm Surge product from NHC, for Hurricane Dennis of 2005.

New Orleans wunderblogger Patrap is at the National Hurricane Conference, and has more info on the conference, for those interested.

Madagascar appeals for aid
Tropical Cyclone Jaya, the sixth tropical cyclone to affect the island of Madagascar this season, has killed three people and caused substantial damage. Jaya hit northern Madagascar as a Category 1 storm earlier this week. The island is suffering through its worst cyclone season on record, and has issued repeated pleas to the international community for aid.

New restrictions on what NOAA scientists can say
NOAA climate, weather and marine scientists will be subject to new restrictions as to what they can say to the media or in public, according to a new policy directive scheduled to take effect in May. I read through the new directive and found it confusing, so I'm not sure what the practical effect of the new guidelines will be. I'll check in later this year with NOAA scientists who might be affected to see if the new policy has had any impact.

My lecture in the Tampa Bay area next week
I'll be giving a free public lecture on Friday, April 13, at Eckerd College in St. Petersburg, Florida. The title of the talk will be, "A Preview of the 2007 Atlantic Hurricane Season--and the Story of a Flight into Hurricane Hugo." The details:

Friday April 13, 4:00 to 5:00 p.m.
Fox Hall
Eckerd College
4200 54th Avenue S
St. Petersburg, FL 33711

Here's a map of where Eckerd College is. I hope to see some of you there! I'll have time after the talk to chat. You can email me at if you have comments about my appearance. Check my blog next Thursday to see if there are any late changes to the talk's time or location, but I'm not anticipating that there will be.

My next blog will be Friday or Saturday. I'll discuss Part 2 of the landmark Intergovernmental Panel on Climate Change (IPCC) 2007 report, which will be released Friday.

Jeff Masters

Hurricane forecasters call for very active Atlantic season

By: JeffMasters, 3:45 PM GMT on April 03, 2007

A very nasty Atlantic hurricane season is on tap in 2007, according to the latest seasonal forecast issued today by Dr. Bill Gray and Phil Klotzbach of Colorado State University (CSU). The Gray/Klotzbach team is calling for 17 named storms, 9 hurricanes, and 5 intense hurricanes. An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The forecast calls for a much above normal chance of a major hurricane hitting the U.S., both along the East Coast (50% chance, 31% chance is normal) and the Gulf Coast (49% chance, 30% chance is average). The Caribbean is also forecast to have an above normal risk of a major hurricane.

The forecasters increased their hurricane activity numbers from their December forecast, citing the rapid dissipation of the winter El Nio event, a forecast of neutral or weak-to-moderate La Nia conditions for the coming hurricane season, plus a continuation of above average sea surface temperatures in the Atlantic.

How accurate are the April forecasts?
I would have liked to have seen mentioned in today's forecast in big bold letters, "our past April forecasts have shown no skill in predicting Atlantic hurricane activity." Don't get me wrong--the CSU team are very skilled scientists, and I like the fact that they are trying to make useful seasonal hurricane forecasts. However, the skill of these April forecasts when compared to climatology is near zero, and they should be stating that in very clear terms in their April forecasts. In fact, CSU April forecasts from 1995-2006 have shown slightly negative skill. Negative skill means that a forecast of the normal climatology of 10 named storms, 6 hurricanes, and 2 intense hurricanes for the period 1995-2005 performed better than the CSU forecast. CSU Forecasts from the past five years have shown some improvement, and have a slight positive skill. The CSU team has posted an Excel spreadsheet of their forecast errors (expressed as a mathematical correlation coefficient, where positive means a skilled forecast, and negative means they did worse than climatology). You can see from their numbers that the December and April forecasts have near zero skill, but the June 1 forecasts have substantial skill. To rectify their poor April forecast skill, the CSU team is trying a new scheme for this year's April forecast. They found that the February-March SST (30-45N, 10-30W), February-March SST (30-45N, 10-30W), and February-March sea level pressure (20-45S, 100-160W) could be used to explain about 55% of the ups and downs of hurricane activity over the period 1950-2004. Hopefully the new scheme will show positive skill forecasting upcoming hurricanes seasons, and not just "hindcasting" the past ones. For now, you're best off just paying attention to their June 1 forecast, which has been quite skillful over the past ten years.

2007 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR), issued a 2007 Atlantic hurricane season forecast today as well. TSR has almost the same forecast as the CSU team--17 named storms, 9 hurricanes, and 4 intense hurricanes. I like how they put their skill level right next to their forecast numbers: 9% skill at forecasting the number of named storms, 15% skill for hurricanes, and 14% skill for intense hurricanes. That's not much better than flipping a coin, but it is better than the slightly negative forecast skill of the Gray/Klotzbach April forecasts. However, TSR doesn't mention the fact that part of their skill may be due to the fact that they issue forecasts of fractional storms--i.e., the numbers they will verify for this April's foreacst are 16.7 named storms, 9.2 hurricanes, and 4.2 intense hurricanes. If we round these numbers to whole storms, the TSR skill numbers may decrease.

TSR projects that five named storms will hit the U.S., with two or three of these being hurricanes. In the Lesser Antilles Islands of the Caribbean, TSR projects two named storms, one of them being a hurricane (50/50 chance of being a major hurricane). TSR cites two main factors for their forecast of an active season: above normal Sea Surface Temperatures (SSTs) are expected in August-September 2007 across the tropical Atlantic, as well as slower than normal trade winds July-September. Trade winds are forecast to be 0.9 meters per second (about 2 mph) slower than average, which would create greater spin for developing storms, and allow the oceans to heat up due to reduced evaporational cooling. SSTs are forecast to be about 0.16 degrees C above normal. TSR gives an 85% chance that the 2007 Atlantic hurricane season will rank in the top third of active seasons observed since 1957.

Figure 1. Accuracy of long-range forecasts of Atlantic hurricane season activity performed by Bill Gray and Phil Klotzbach of Colorado State University (colored squares) and TSR (colored lines). The CSU team's April forecast skill is not plotted, but is near zero. The skill is measured by the Mean Square Skill Score (MSSS), which looks at the error and squares it, then compares the percent improvement the forecast has over a climatological forecast of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TS=Tropical Storms, H=Hurricanes, IH=Intense Hurricanes, ACE=Accumulated Cyclone Energy, NTC=Net Tropical Cyclone Activity. Image credit: TSR.

Landmark greenhouse gas emissions ruling by the Supreme Court
The Supreme Court yesterday ruled that the EPA has the authority to regulate CO2 as a pollutant. An analysis of this ruling is presented by Dr. Ricky Rood today in our Climate Change blog. This could well prove to be the Supreme Court's most important environmental decision ever.

Jeff Masters

Another Madagascar cyclone; first typhoon of the season

By: JeffMasters, 3:31 PM GMT on April 02, 2007

We don't pay much attention to Madagascar, the impoverished island of 18 million off the southeast coast of Africa. However, that island has seen a remarkable series of devastating tropical cyclones during the current Southern Hemisphere hurricane season, which peaks in March and is now in its waning months. Tropical Cyclone Jaya, a Category 2 storm poised to strike the island on Tuesday, is the sixth tropical cyclone to bring heavy rains to the island since December--the most number of cyclones to affect the island in such a short period of time. The previous storm, Tropical Cyclone Indlala, hit Madagascar on March 15, killing 80 and leaving 105,000 homeless. The torrential rains of Indlala, in addition to setting world rainfall records for a 72-hour period on nearby La Reunion Island, flooded much of northern Madagascar, wiping out large portions of the rice crop. Earlier this year, 45,000 Madagascarans were left homeless by Cyclone Bondo (25 December 2006), Cyclone Clovis (3 January 2007), Cyclone Favio (18 January 2007), and Cyclone Gamede (26 February 2007). In addition, the seasonal rains have been heavier than usual this year, as the Inter-Tropical Convergence Zone (ITCZ) has been further south than normal.

Jaya is a small cyclone, and is not expected to bring more than about six inches of rain to northern Madagascar. However, the island has not recovered from the flooding from the previous five cyclones, and Jaya's rains will cause great hardship. Madagascar has appealed for $242 million in international aid to help put the country back together.

Figure 1. Visible image of Category 2 Tropical Cyclone Jaya at 06:45 UTC February 2, 2007, as it approached Madagascar. Image credit: NASA.

First typhoon of the year
In the Western Pacific, we have our first typhoon of the 2007 typhoon season, Category 1 Kong-rey. This is a fairly typical time to get the first tropical cyclone in the Western Pacific, where the waters are warm enough year-round to support typhoons. Kong-rey is expected to pass through the Mariana Islands north of Guam as a Category 1 storm, and recurve out to sea. Some of the global computer models we use to forecast hurricanes--the GFS, NOGAPS, and ECMWF--did a remarkable job forecasting the formation of this typhoon as early as seven days in advance. Hopefully, this skill will extend to the coming Atlantic hurricane season!

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™


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