Isaac becomes better organized, remains a tropical storm

Isaac is gradually becoming better organized this afternoon, with winds of 60 mph and a minimum central pressure of 992 mb. A hurricane warning has been issued for the northern Gulf Coast, including Louisiana and the Florida Panhandle. Strong thunderstorm activity has developed around the inner core of the storm, which is visible on both satellite and radar. This afternoon's Hurricane Hunter mission has found surface winds from 50 mph to 65 mph and steadily dropping pressure--a sign of a strengthening cyclone. Late in the flight, the hunters found a shift in the center to the west, which could either be a trend or just a "wobble," and could readjust. Another mission is on its way to the storm. Upper level outflow remains organized on the north side of the storm, but wind shear remains moderate (10-20 knots) to the south and southeast of Isaac, disrupting the development of organized thunderstorm activity there.

The Sombrero Key, Florida buoy is reporting sustained wind speeds around 50 mph with gusts close to 60. A weather station in Dry Tortugas National Park is reporting sustained wind speeds around 35 mph with gusts up to 45 mph. A tornado watch has been issued for southern Florida, and some storms with weak rotation have been spotted, but no tornado warnings have been issued. Heavy rain is falling in the Keys and southern Florida, and radar-estimated rainfall totals thus far are up to 4 inches. Scattered storms associated with Isaac reach as far north as St. Augustine, Florida this afternoon, and the storm's main rain shield is approaching Orlando.

Some Florida rainfall totals so far:
• Homestead: 6.26”
• Miami: 2.67”
• West Palm Beach: 1.73”
• Key West: 1.37”


Figure 1. Satellite imagery of Tropical Storm Isaac from around 2pm EDT on Sunday.

Track Forecast
Like this morning, the models are still disagreeing on exactly where Isaac will make landfall. The ECMWF's track remains the farthest east, and forecasts Isaac to make landfall near the Florida/Alabama border. Next to the west is the UKMET, which is predicting landfall near Mobile, Alabama. The HWRF, GFDL, and GFS are all on the western side of the envelope, with the GFDL and the GFS predicting landfall in western Louisiana, possibly close to the Louisiana/Texas border. In terms of landfall timing, it depends on the track, but we're expecting landfall early Wednesday morning. The National Hurricane Center's 5pm EDT track splits the difference between the GFS model, which is the western solution, and the ECMWF, which is the eastern. They predict Isaac will continue to move northwest over the next day or so before turning slightly to the north before approaching the Louisiana/Mississippi coastline on Tuesday afternoon and evening.

Intensity Forecast
The HWRF model continues to be the most bullish on Isaac's potential intensity, forecasting the storm to reach category 3 status. The GFDL is more reserved and suggest Isaac will only reach strong category 1 wind speeds before making landfall. Given current observations, the National Hurricane Center has backed off the previous forecast that Isaac will intensify to hurricane status around the Florida Keys. They now expect Isaac to remain at tropical storm status as it moves through the central Gulf of Mexico before finally strengthening as it approaches the coast and become a category 2 hurricane just before landfall.


Figure 2. Model forecasts of Isaac's potential track.

Portlight update

"We are coordinating a pro-active response to potential Hurricane Isaac's landfall along the Gulf Coast. This pro-active response is a major step forward for Portlight and would not have been possible without each of you that have been involved over the past four years since our large scale disaster relief effort after Hurricane Ike devastated the Texas Gulf Coast. The response to Hurricane Ike was a profound effort of everyone working together which accomplished a lot of great things including repatriating BillyBadBird, feeding the Bolivar Peninsula, delivering needed supplies to Bridge City, Tx (which was inundated by Ike's surge), providing medical equipment to the disabled, and the heart warming Christmas Party for the residents of Bridge City, Tx. It was truly a group effort and none of it would have been possible if we had not had so many step up, get involved, and provide support and assistance in whatever way each individual could."

You can donate to Portlight's disaster relief fund here.

Dr. Masters will have an update tomorrow morning, and you can catch him on The Weather Channel throughout the evening.

Angela