Isaac Headed For The Gulf Coast

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TODAY: Before we get into Isaac, let’s point out that today should be a beautiful day across the great state of Alabama, with a good supply of sunshine and a high at or just over 90 in most places as we will be in the subsidence band (sinking air) on the periphery of Isaac.

ISAAC THIS MORNING: Still a tropical storm packing sustained winds of 65 mph, Isaac is northeast of Key West, and is moving to the west/northwest at 14 mph. It still seems like dry air is involved in the circulation, which is keeping Isaac from strengthening rapidly. Also, the circulation is very large, and not small and tight, which is another reason the system is just having a hard time getting stronger.

LANDFALL: NHC has adjusted their track westward a bit in response to the model set. They now bring it into Southeast Louisiana as a category one hurricane tomorrow night, with a continue movement to near Vicksburg, and on into Arkansas as a weakening tropical system. Outliers remain… the ECMWF and the RPM are closer to Gulf Shores/Pensacola, but most models are fairly close to the NHC track. We also note the GFS does not bring Isaac northward as soon as NHC; it makes the turn near the Texas/Louisiana border. So, there is still some uncertainty, but the overall confidence is certainly a bit higher this morning.

But remember, like we always say, don’t focus too much on that center line; the impact of the system, especially to the east of the center, can extend for several hundred miles.

INTENSITY: NHC brings Isaac to the coast as a category one hurricane, and I am beginning to think they are correct. The large circulation makes it harder to intensify… it needs to bring itself in, much like an ice skater brings their arms in to spin faster. Not sure this will happen. Also it seems like drier air is involved on the west and south side of the circulation. But, there is plenty of very warm ocean heat content, and we will watch to watch for surprises.

COASTAL IMPACT: Mandatory evacuations begin this morning at 8:00 for Dauphin Island, and evacuation zones 1 and 2 in Mobile and Baldwin Counties (scroll down a bit for a post that shows those zones). A hurricane warning remains in effect from near Morgan City, Louisiana to Destin, Florida, including all of the Alabama Gulf Coast.

If Isaac does remain a category one hurricane with landfall over Southeast Louisiana, there won’t be much structural damage on the coast from wind. Storm surge of 5 to 10 feet will certainly cause some coastal flooding, and the soaking tropical rain will bring some flooding as well. Rain amounts of 5 to 10 inches are likely along the east of where Isaac makes landfall on the coast.

IMPACT FOR NORTH/CENTRAL ALABAMA: Again, we will write this assuming the NHC track is correct. For places like Tuscaloosa, Birmingham, Anniston, and Gadsden, showers could begin as early as tomorrow afternoon, with tropical rain bands more likely tomorrow night into Wednesday. We will project rain amounts of 2 to 4 inches here in the period Tuesday night through Thursday, with some potential for flash flooding. Should the center be a little closer to Alabama, those numbers could go higher.

In terms of gradient wind (the sustained winds we feel), with the track being pretty far to the west, they should be in the 15-25 mph range here, meaning no widespread tree and power line damage, although some scattered outages are possible. We will not recommend that people leave mobile homes in this kind of situation.

TORNADOES? Perhaps the biggest issue we will deal with is the potential for small tornadoes in the spiral rain bands wrapping around the center of Isaac. Understand these are not like the violent tornadoes of spring and fall, but they still have the potential to produce significant damage, and tornado warnings are issued for them. SPC has much of Alabama in the standard “slight risk” of severe weather tomorrow night and Wednesday, and we will have to watch the radar closely. These small tornadoes are low topped, hard to provide warnings for, and don’t last long.

TRAVEL: First off, for those flying to Dallas for the Alabama/Michigan game, the westward track means that there is a pretty good chance that there won’t be any serious delays at Birmingham Shuttlesworth Airport this week, but if a tornado warning is issued that includes downtown Birmingham, there might be a ground stop or two along the way. The main impact of Isaac will be east of Dallas, and the weather in Texas looks mostly dry and pleasant on Saturday.

Driving through Alabama tomorrow night though Thursday no doubt will be wet at times, but with the most significant flooding expected to be west of here, over Mississippi, you should be able to get to your destination. But have a way of hearing tornado warnings as some could very well be required.

LABOR DAY WEEKEND: For Alabama and the Gulf Coast, Isaac will be long gone by the Labor Day weekend, but we will remain in a very moist tropical airmass, so we expect at least scattered showers and storms Saturday through Monday. It won’t rain all weekend, and the sun should be out at times, but just be aware that a few tropical downpours are very possible along the way.

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Tags: Isaac

Category: Alabama's Weather