Weather Nerd

Gustav scenarios

Amid all the bad news surrounding Hurricane Gustav, I’m thrilled to discover that one of the best weatherbloggers of the 2005 hurricane season, Charles Fenwick, has returned from Iraq, where he had been stationed since being recalled to active duty a year ago, and is blogging again.

I know I speak for everyone when I thank Charles for his service. Meanwhile, I’ll be adding his Eye of the Storm blog to my blogroll, and to my personal list of “must-read” weatherblogs, along with Jeff Masters, Eric Berger and Alan Sullivan.

Speaking of Sullivan, he has a good post on the possibilities for Hurricane Gustav. He writes, in part:

Later tonight Gustav will emerge into the extreme SE Gulf of Mexico. It will be interesting to see how it fares there. The ocean is very warm, and upper winds should remain favorable. There is a lot of talk about potential for category five status when Gustav crosses those waters SW of Florida. The lower Keys will be sideswiped by squalls near hurricane force; it’s already very stormy there as I write. But what of Louisiana?

Gustav has wobbled a bit in its course today. This is normal for strong hurricanes. Smoothed out, the trendline still runs toward the Texas-Louisiana border. (Correction: 1800 UTC extrapolation aims further east, and closer to New Orleans.) I have studied the time-lapses again and again, for the hurricane itself, and especially for the larger environment. I am getting more confident that Gustav will make landfall close to where Audrey did 51 years ago [in southwestern Louisiana]. But there are several differences.

First, Gustav will be encountering a less favorable marine layer as it nears the coast. Second, it will be moving more slowly than Audrey, and it will have more time to entrain continental air. Third, and perhaps most important, it will be approaching the coast at an oblique angle. This means it will spend more time over the coastal waters, and its surge will not be driven ashore with maximum force.

Of course as Gustav crosses the Gulf, everyone will be watching for any deviation in course to the right. That would put New Orleans in dire peril. Even a weakening Gustav could swamp the city again. But that will only happen if the eye comes ashore at an angle that brings it immediately SW of the urban area. Not quite threading a needle, but almost. Unfortunately several of the 1800 UTC models cluster on this line, while others continue to aim at SW Louisiana.

Another possibility is deviation to the left. But that would steepen Gustav’s angle of approach to the coast, and give it even more time to weaken. There is definitely a threat of some very bad weather in SE Texas, but I would expect the storm to be much diminished before landfall, if it swerves that way.

Berger also has a good post about four possible scenarios for Gustav, which he lists “in order of most likely to least likely”:

1. Central Louisiana landfall, moves inland: This scenario basically follows the GFDL model and the official track forecast. A major hurricane slams into the Louisiana coast just east of New Iberia. The storm slows as it moves inland and perhaps stalls over northeast Texas. There’s lots of rainfall in Louisiana and east Texas, including Houston. The storm hits Lake Charles and Baton Rouge hard but other major population centers are largely spared damaging winds.

However if Gustav comes in as little as 50 miles west of New Iberia the Beaumont-Port Arthur region will receive some nasty winds, although not as bad as Rita.

2. Central Louisiana landfall, stalls: In such a scenario, similar to theHWRF model, Gustav makes landfall in central Louisiana as a major hurricane and moves inland for a short period of time. In one to three days, however, it moves back offshore and may re-strengthen before ultimately striking Texas. In such a scenario Texas is probably spared catastrophic winds but there is a potential for significant flooding.

3. Eastern Louisiana landfall: Perhaps after taking a northward jog off Cuba, Gustav makes landfall east of Morgan City as a major hurricane. As I have described below, such a scenario is potentially catastrophic for the city of New Orleans, which would face a massive storm surge.

4. Upper Texas coast landfall: Before Gustav reaches the central Louisiana coast the storm bumps into a high pressure system, which bends it westward toward Texas. Depending how close Gustav comes to shore, this scenario could bring a major hurricane to Texas.