There is a lot to cover tonight on the blog as Tropical Storm Isaac is about 75 miles southwest of Key West.
The 8 pm EDT advisory has Isaac 24.2N 82.9W, and moving WNW (285 degrees) at 14 mph. Max winds have jumped a bit to 65 mph with a minimum central pressure of 993 mb. The storm has been doing some interesting things for the last few hours. The tropical storm has increased thunderstorm activity around the center of circulation – mainly around the western side – based on satellite imagery. It gives the appearance that Isaac is beginning to get its act together. Regardless, latest recon data doesn’t necessarily show any intensification of the storm.
The radar imagery has given the appearance that Isaac was moving more northerly than northwest. But it’s not happening as the 11 pm EDT advisory shows Isaac moving west-northwest at 14 mph.
The thing that will keep Isaac tempered is the drier air off to the south and east of the storm. A lot of the convection seems to be on the western side, but the counterclockwise flow is bringing more drier air around it. Also, there is a lack of good convection on the southern half of the storm – the convection is asymmetric at this point. The dry air is also being pulled in by an upper-level low just to the west of Isaac.
The future track of Isaac remains to be very uncertain as the guidance models continue to jump around. There are some factors at play. One is the ridge off to the east of Isaac and the second is the aforementioned upper-level low to the west. The low is expected to move westward away from Isaac (see the GFS’ scenario below). This can do two things: 1) It will help cut the dry air intrusion in Isaac and 2) help steer Isaac northwest.
Here’s where things can get tricky: Most of the models – except for the Sunday morning European – have taken a shift to the west to Louisiana. With all of the shifting that has taken place, my confidence in the guidance models remains low. Everyone on the gulf coast needs to keep an eye on this. Floridians living in the panhandle should not breathe a sigh of relief just yet.
The intensity is also uncertain. If this upper low moves away – and the models expect it – Isaac has a chance to gain strength. The NHC is thinking category 2 strength (96-110 mph) before landfall. I see it as a reasonable forecast. But I’ve seen intensity surprises before (think of Hurricane Charley in 2004). The gulf waters continue to be in the mid 80s – even higher in some spots, so there is a possibility of further intensification. One good glimmer of hope is that the depth of the warm water isn’t as great as it has been in the past, so the fuel isn’t as abundant. Still, whether it’s a cat 2, or 3, or 4, or, hell, even a 1, people still need to prepare for the possibility of storm surge, flooding, strong winds, and a threat of a tornado or two inland.
Hurricane warnings are in effect on the gulf coast from east of Morgan City, La. east to Destin, Fla. People living in those areas should heed any evacuation orders from local officials. The time to prepare is now.
Expect the next full update to be sometime Monday evening. Keep checking our Twitter and Facebook feeds for the latest info and brief analysis on Isaac.