Weather Nerd

A Word of Caution

[NOTE: For my latest updates on Hurricane Sandy, follow me on Twitter.]

Hurricane Sandy may be downgraded to a tropical storm tonight at either 8:00 PM or 11:00 PM Eastern. In fact, Sandy may technically already be a tropical storm; the National Hurricane Center’s 5pm discussion suggests that the data doesn’t strictly support its classification as a hurricane right now, but the NHC is waiting for additional reconnaissance data to confirm weakening before formally downgrading it. If such data comes in, the storm will likely be downgraded tonight. And yes, it looks terrible on satellite right now.

Do not be fooled by this. This was expected. Forecasters knew Sandy would struggle with wind shear today. The computer models foresaw that. Sandy’s struggles, thus far anyway, are not a bearish long-term sign for the storm’s future development. They are precisely what was expected.

For some time now, the forecast has called for Sandy to struggle with wind shear Friday/Saturday, then re-organize and intensify Sunday/Monday/Tuesday as it slips into a more favorable atmospheric environment — sort of a calm in between the nearby heavy-shear zones — and also moves over unseasonably warm Gulf Stream waters. At that point, the expectation is that it will begin to strengthen and deepen (i.e., its pressure will drop), possibly through a potent combination of tropical and baroclinic processes (though it appears likely to remain a warm-core system until landfall). Come Monday night and Tuesday, the models show Sandy “bombing out,” as a shortwave trough zips in to the south, wraps around’s Sandy warm core vortex, and explosively intensifies it. Somewhere around this time, something that I frankly don’t fully understand called a “tropopause fold” gets involved (maybe), and a reinvigorated, terrifyingly intense storm slams into the coast of the Megalopolis.

That’s what the models foresee. I freely admit there’s no guarantee it will play out that way — and indeed, it would be wonderful if the models are wrong, and Sandy doesn’t strengthen as much as they predict. That would be great news! But it’s not news that we can trumpet yet. There’s no sign yet of it happening. That’s the point: Sandy’s disorganization and weakening today DOES NOT suggest that the models are wrong about Sandy’s future strengthening, because what’s happening now is precisely what the models expected. So, as of this writing, we still don’t have any concrete reason to suspect that Sandy won’t become the disaster we fear.

I’m posting this as a forewarning against complacency — and because my head may explode if (when) people start saying, “See?! Sandy was overhyped!!!” when it’s downgraded tonight.

If I see any indication that Sandy is looking like it might be less-bad than feared, I promise I will tell you, as I have with previous storms like Isaac, Irene, etc. But as of yet, with this storm, I see no such indications.