Here Comes Gustav

Another potentially dreadful scenario looms for SE Louisiana, and perhaps Mississippi and Alabama coastal areas. But the hurricane has some healing to do first.

Even with a fast motion across a very narrow part of Cuba, the eye got shredded a bit. The Loop Current and some eyewall re-contraction ought to repair the damage to the core structure, but there are cold eddies off the edge of the Loop Current that might offset gains the storm makes from the high OHC. I’m not convinced yet that this is going to rival Katrina, but there’s plenty of time still. And if it does go berserk over the LC, there’s plenty of precedent from 2004-5.

Several U.S. tornado chasers are planning hurricane intercepts in Louisiana. I think chasing a hurricane in Louisiana is borderline insane for logistical reasons, but hope they give us some good observations and don’t need to be rescued…or worse. I posted the following elsewhere…

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Don’t forget to factor in the contraflow logistics of the highways if you’re thinking of chasing Gustav in LA. Many roads will be running one-way-out, only. And this should go without saying, but NOLA/SIL areas and anything near Lakes Pontchartrain/Maurepas/Borgne should be avoided at all costs.

Good luck to anyone planning to chase this in LA. You’ll need it. The strategy of taking plenty of fuel is wise because it will be scarce. Whatever is essential to escape and survival of humans and equipment — load up on spares (e.g., fuel, food, water, tires, waterproof coverings/bags, chain saw, first aid kits, etc.).

I love chasing hurricanes and being in them, but unfortunately the opportunity just doesn’t present itself very often. Even if it did this time, I wouldn’t go because of where it is, the lack of roads near the coast, and the unsafe nature of the few that are with respect to storm tide levels, potential blockages and freshwater flooding. Give me the middle-upper TX coast (outside of Houstink), FL Panhandle/Peninsula or Carolinas any day for observing hurricanes…but not Louisiana. Bad news.

Above all else…stay safe. We don’t want to lose anyone here.

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I cannot state that plea strongly enough — stay safe! I absolutely, positively don’t want any storm observers hurt or killed out there. Not in the past, not now, not ever.

I’ll be watching this one from the mesoscale desk at my unnamed workplace, and from home when not on shift. Might even BLOG about it some more if there’s some time. [On a personal level, I pray that my pre-Katrina fears about New Orleans don’t come true again!]

We severe storms forecasters at the unnamed center surely will have some tornado related forecasts going (outlooks, MCDs, watches). Should be fun and challenging from a tornado prediction pespective, as they all are.

Some forecasting tips for TC tornadoes…

Of the four needed ingredients for tornadic supercells (moisture, instability, lift, shear), two are there in ridiculous abundance in a landfalling or newly inland hurricane: moisture and shear. Lift is subtle outside bands, strong in them, but the crappy lapse rates aloft also bottom out with weak or no substantial capping in the typical TC environment. A big wind envelope increases the area of large 0-1 km hodographs and the area covered by a wind environment favorable for supercells. This is one reason why Katrina and Ivan produced so freaking many tornadoes…they were big as well as strong and long-lived.

Instability is a huge key. TC tornadoes can and do happen at night, but climatologically, peak during the day. This is no accident. Surface thermal analysis (every 1 or 2 deg F) especially within the outer ~340-120 Cartesian degree sector (NE quad plus some cushion either side) of the envelope is critical. This is particularly true by day when insolation in cloud breaks and dry slots tends to create or magnify inhomogeneities (baroclinic features like differential heating boundaries) and thermal axes. A hurricane is an MCS, and can and should be mesoanalyzed! In addition to supercells either alone between bands or embedded within them, watch for those supercells or even strong, persistent nonsupercellular convective elements that are about to cross any thermal inhomogeneities.

Integrate satellite trends, radar echo loops, VAD wind profile tendencies, upper air maps and environmental mesoanalyses into a 4-D diagnostic model in your mind, and TC tornado prediction becomes much less mysterious. Still challenging, to be sure, but with success achievable.

In 12 hourly upper air analyses, watch for areas and especially gradients of drying aloft, per Lon Curtis’ study on upper drying in TC tornado outbreaks. Bill McCaul’s climatologies showed CAPE tends to increase outward away from the CDO where more opportunities exist for (differential) heating. My experience analyzing and forecasting TC tornado situations bears all this out.

Also remember that the storm spins down slower just above the surface than at the surface, so hodographs in the NE quadrant, at least 1-2 days inland, still can be really big; because even as the surface winds weaken, the shear stays large. Alas, the favorable tornado envelope for Gustav, based on NHC’s forecast track, will cover lots of pine forests where actually observing tornadoes would be a huge challenge, to say the least — even more so than low cloud bases, rain, and small, transient nature of most TC tornadoes typically presents. Another reason I rather would chase hurricanes in south Texas…



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