Ike intensifying explosively

By: Dr. Jeff Masters , 1:25 AM GMT on September 11, 2008

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Hurricane Ike is intensifying dramatically. The central pressure has dropped 11 mb in just four hours, and stood at 947 mb at 7 pm EDT. The latest Hurricane Hunter data show that the pressure is continuing to fall at a rapid pace. The winds have not caught up yet to the pressure fall, and remain at Catgeroy 2 strength. The satellite presentation of the hurricane has improved markedly, as Ike has walled off the dry air that was bothering it, and has built a solid eyewall of 9 miles diameter of very intense thunderstorms. The appearance of Ike on infrared satellite loops is similar to Hurricane Wilma during its rapid intensification phase, when Wilma became the strongest hurricane on record. Like Wilma, Ike has a very tiny "pinhole" eye, but the storm is huge in size. Ike has a long way to go to match Wilma, but I expect Ike will be at least a Category 3 hurricane by morning, and probably a Category 4.


Figure 1. Experimental storm surge heights for Ike. There is a 10% chance the storm surge from Ike will exceed these values. Data courtesy of NOAA.

Ike is almost as large as Katrina was, and this large wind field is already beginning to pile up a formidable storm surge. Tides are running 2-4 feet above normal along the Gulf Coast from Louisiana to the west coast of Florida. Tides have risen one foot above normal in Galveston too. The water level will continue to rise as Ike approaches Texas, and NOAA's experimental storm surge forecast (Figure 1) is calling for a 10% chance that the storm tide from Ike will reach 10-12 feet at Galveston, and 18-21 feet on the south and east sides of Houston.

Ike is likely to be a extremely dangerous major hurricane at landfall, and will likely do $10-$30 billion in damage. The chances of hundreds of people being killed in this storm is high if people do not heed evacuation orders. It is possible that Ike will make a direct hit on Galveston as a Category 4 hurricane with 145 mph winds. The potential storm surge from such a hit could be in the 15-25 foot range (Figure 2), which is capable of overwhelming the 17 foot sea wall in Galveston. I put the odds of such an event at about 5%.


Figure 2. The maximum storm tide (storm surge plus an adjustment for hitting at high tide) expected from a mid-strength (145 mph) Category 4 hurricane hitting anywhere along the coast of Texas at high tide. This so-called "MOM" (Maximum Of the Maximum Envelope Of Waters) is computed using NOAA's SLOSH storm surge model. The plot above IS NOT the expected storm tide everywhere along the coast from a hit by Hurricane Ike. The plot is the MAXIMUM high water for a worst-case scenario Category 4 hurricane moving at the worst possible angle at the worst possible forward speed. As such, this plot is the combination of SLOSH runs from over 50 different simulated hurricanes approaching the coast at different angles and different forward speeds. The maximums plotted here are only possible along a 20-mile stretch of the coast on the north side of Ike's eyewall. SLOSH model runs are advertised as being in error by plus or minus 20%. Image credit: NOAA.

Track forecast for Ike
The latest 18Z (2pm EDT) computer models are still in poor agreement. The GFDL still has Ike making landfall at Galveston as a borderline Category 3 or 4 hurricane, and the rest of the models have landfall farther south, near Port O'Connor. With a trough of low pressure expected to turn Ike northwestward close to landfall time, slight variations in the timing of this trough among the models is causing a large spread in landfall locations. The cone of uncertainty still covers the entire Texas coast, and residents of southwestern Louisiana are also at risk.

I recommend Texas residents consult NHC's wind probability product to determine their odds of getting hurricane force winds. At 5 pm EDT, NHC called for these odds of getting hurricane force winds at various Texas cities:

Corpus Christi: 15%
Port O'Connor: 26%
Freeport: 30%
Galveston: 25%
Houston: 20%
Port Arthur: 13%

As you can see, Freeport is considered the most likely city in Texas to receive hurricane force winds. I believe the percentages for the cities above are too low, and should be bumped up by 5-10%.

Intensity forecast for Ike
The intensity forecast remains the same. Water temperatures are a warm 29.5°C in the Gulf of Mexico, and wind shear is expected to be modest, 10-15 knots, for the remainder of Ike's life. Ike will be skirting the edge of a warm Loop Current eddy, but the heat content of the waters near the Texas coast are high. Ike has the capability of intensifying right up to landfall. This is the forecast of the HWRF model, which has Ike hitting Port O'Connor as a Category 4 hurricane with 145 mph winds. The weakest I think Ike will be at landfall is a Category 2 hurricane with 100 mph winds. Even at this weak strength, Ike will still carry a 10-15 foot storm surge to a 100+ mile long stretch of Texas coast.

Storm surge risk
We've put together today a page of storm surge risks for the Texas coast. These images show the maximum storm tide (storm surge plus an adjustment for hitting at high tide) expected from a mid-strength hurricane of each Saffir-Simpson Category hitting anywhere along the coast of Texas at high tide. These so-called "MOMs" (Maximum Of the Maximum Envelope Of Waters) are computed using NOAA's SLOSH storm surge model. A sample image is shown in Figure 1 for a Category 4 hurricane affecting the Galveston area. A storm of this magnitude is expected to bring a maximum 22 foot storm tide (storm surge plus a 2-foot adjustment in case it hits at high tide) to Galveston. A maximum 28-foot storm tide could affect the built-up areas along the east side of Houston. Note that some Category 4 hurricanes making a direct hit on Galveston will bring a significantly lower storm surge than the worst-case 22-foot scenario pictured here. For example, the Great Galveston Hurricane of 1900 was a Category 4 storm that hit the city head-on, but generated a storm surge of only 15 feet. Even so, this hurricane was the deadliest disaster in American history, killing an estimated 8,000-12,000 people. Since then, Galveston has built its seawall to a height of 17 feet, which would probably withstand a direct hit by Ike at Category 4 strength.

For storm surge evacuation zone information, consult the Texas Division of Emergency Management.

Links to follow
Tide gauges along the Gulf Coast

Storm surge risk for the Texas coast

I'll be speaking at hurricanecity.com tonight at 9:30pm EDT. I'll be posting a new blog Thursday morning.

Jeff Masters

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1. tampariver
2:30 AM GMT on September 13, 2008
GOD help you all,WHO DID NOT LEAVE,I HOPE YOU DID NOT HAVE KIDS WITH YOU AND WERE SMART ENOUGHT TO GET THEM TO SAFE PLACE...GOD BE WITH ALL THAT DIE TONIGHT :(

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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