Ike headed into the Bahamas, and is a major threat to Haiti, Cuba, and the Keys

No significant changes have occurred today to Hurricane Ike, and the hurricane remains a borderline Category 2 or 3 storm headed west-southwest towards the Southeastern Bahamas. Infrared satellite loops show little change in the amount or intensity of Ike's heavy thunderstorms, and shear of 25 knots continues to restrict upper level outflow on Ike's northwest side. The eye is showing up intermittently, and Ike is holding together very well for being under so much shear.

Track forecast for Ike
The latest 06Z (2 am EDT) computer models foresee a probable direct hit by Ike on Grand Inagua Island in the Southeast Bahamas, with the Turks and Caicos Islands also getting hit hard. The eye is about 27 miles in diameter, so a region about 50 miles wide will feel Category 3 hurricane winds in the Southeast Bahamas. These islands can expect a storm surge of 6-12 feet, and extreme damaging winds. Ike will pass 40-80 miles north of northwestern Haiti, and will bring rains of 3-6" to the Dominican Republic, and 4-8" to northern Haiti. These rains will likely cause additional severe flooding in Haiti, where the death toll is nearing 200 in the aftermath of Hurricane Hanna.

All of the major models agree that Ike will hit eastern Cuba on Sunday night. After this point, the models diverge. A southern camp of models, the ECMWF and UKMET, take Ike across eastern Cuba and into the western Caribbean, then through the narrow Yucatan Channel between Cuba and Mexico's Yucatan Peninsula, eventually hitting Texas a week from now. This track would bring tropical storm conditions to the Cancun/Cozumel area beginning Tuesday afternoon or evening, with possible hurricane conditions by Wednesday morning.

The northern camp of models, including the GFS, NOGAPS, GFDL, and HWRF, turn Ike west-northwest over Cuba, forecasting that Ike will pop off the coast of Cuba near the Florida Keys on Tuesday, then swing north to threaten the west coast of Florida. The NOGAPS and GFDL both forecast that Ike will pass within 50 miles of Tampa on Thursday, while the GFS and HWRF put Ike several hundred miles off the west coast of Florida. I'm leaning towards this northern solution, since the GFDL model has been performing so well for both Ike and Gustav. The GFDL forecasts Category 3 strength winds will affect Key West and the Upper Keys, despite a track by Ike over Cuba.

Florida Keys are at very high risk from Ike
The Florida Keys are highly vulnerable to hurricanes, thanks to the presence of but one road out of Key West. The entire chain of islands is in a Category 2 or 3 evacuation zone, and will be inundated by a direct hit from a Category 2 or 3 hurricane. During Hurricane Donna of 1960, a storm surge of 4-13 feet affected the Keys (Figure 1). Donna was a Category 4 hurricane when it passed through the Lower Keys. In general, a Category 4 hurricane moving WNW like Ike is expected to bring a maximum storm tide (storm surge plus a correction for if the hurricane hits at high tide) of 9-10 feet (Figure 2). I believe there is a 30% chance Ike will bring Category 2 strength winds or higher to the Keys, with the Middle and Lower Keys being the most likely targets. this is higher than the NHC Wind Probability Product forecast, which gives Key West a 15% chance of receiving hurricane force winds from Ike.


Figure 1. Observed high water marks in the Keys from Hurricane Donna of 1960. Image credit: "Characteristics of the Hurricane Storm Surge" by D. Lee Harris, U.S. Weather Bureau, 1963.

Intensity forecast for Ike
Sea surface temperatures (SSTs) have warmed to 29.5°C underneath Ike and will warm to 30.0°C over the Gulf of Mexico. Shear is 25 knots this morning, and is forecast to drop below 10 knots tonight. Ike should start intensifying tonight. Landfall on Cuba will significantly disrupt the storm, and Ike's strength as it passes the Keys is difficult to guess at this point. The most likely strength is a Category 2, but it could easily be a Category 1 or 3, depending on how long the storm stays over Cuba, and the exact track through the Keys. Once Ike enters the Gulf of Mexico, shear is expected to be low to moderate (10-15 knots), and the ocean is warm, so additional intensification is likely.


Figure 2. Expected maximum storm tide (storm surge plus adjustment for hitting at high tide) from a Category 4 hurricane moving WNW at 15 mph through the Florida Keys, hitting at high tide. This plot is an ensemble of many different hurricane tracks (shown as black lines), not just one hurricane. The maximum surge from the ensemble is plotted here. The model used is NOAA's SLOSH model. Note that ocean side surge is a foot to two feet lower than bay-side surge. Bay-side surge comes well after the storm center has passed the Keys, from the westerly winds behind the storm. Too many people have been harmed because they thought it was safe to go near the water on the bay side just after a storm has passed. Image credit: Dr. Stephen Baig, NOAA (retired).

How will Ike affect the Miami area?
Don't get fixated on the official forecast or the computer model tracks showing Ike passing to the south of Miami through the Keys or over Cuba. Miami is still in the cone of uncertainty, and is at risk from a direct hit by a Category 4 hurricane. I'd put the odds of a direct hit by Ike on the East Coast of Florida north of the Keys at around 20%. NHC's Wind Probability Product is giving Miami at 10% chance of experiencing hurricane force winds. If Ike follows the 5 am EDT official forecast, passing to the south of Miami along the north coast of Cuba, the expected region of tropical storm force winds will fall just south of Miami, though (Figure 4).


Figure 3. Radius of tropical storm force winds (green colors) and hurricane force winds (yellow colors) along the 5 am EDT Sat 9/6/08 NHC forecast track of Ike. Image was taken from our wundermap for Ike, by clicking on the "hurricane" layer and "wind radius" layer. Note that NHC does not issue a forecast of hurricane force winds for the later time periods, so no yellow colors are shown where Ike is south of Florida.

I'll have a full blog entry this afternoon at about 4pm.

I'll be on the radio on the "Science Fantastic with Dr. Michio Kaku" show Saturday at 5:20 pm on http://talkradionetwork.com/. It's a call in show, so you can ask questions.

Jeff Masters