Weather Nerd

Isaac May Pose Major Evacuation Dilemma

Tampa Mayor Bob Buckhorn caused a sensation earlier Wednesday when he told CNN that “absolutely we’re prepared to” call off next week’s Republican National Convention if Tropical Storm Isaac makes it necessary. Buckhorn is a Democrat, so of course this caused immediate talk of possible political motives:

Buckhorn is an Obama fan. He said of a Barack Obama speech in June, “The president laid out a blueprint today that will create value-added jobs, grow our economy and tackle the deficit. He made it clear to us in Tampa that he has the right vision to guide this nation’s economic future.” If there is legitimate danger to the population of Tampa, he certainly has the responsibility to cancel the convention. But if he’s too quick on the trigger, we’ll all know why.

The trouble is, the way Isaac’s path and intensity forecasts are evolving, it may not be all that easy to differentiate “legitimate danger” from “too quick on the trigger.” It is entirely possible that an evacuation will be absolutely necessary — and yet will look completely silly in retrospect, at least superficially.

Here’s the thing. Isaac is presently expected to basically parallel the northeast coast of Cuba, then basically parallel the west coast of Florida. That forecast could still change drastically — computer models Wednesday have been calling for scenarios as divergent as a New Orleans catastrophe and a Category 4 strike on Florida’s east coast, and plenty of other possibilities to boot — but if Isaac stays on the basic path that the NHC is currently projecting, this is going to be an unusually tricky wicket for forecasters and planners, made even trickier by the RNC.

If Isaac follows roughly the expected track over the next 72 hours, I suspect that the forecasts of U.S. landfall location and intensity will remain highly uncertain, unusually late in the game, simply because of the storm’s angle of approach and proximity to land. With this large storm approaching at the expected angle after hitting Hispaniola and Cuba, the Tampa Bay area — and other places in Florida — would be forced to make important preparedness decisions (including, possibly, whether to postpone or cancel the RNC) at a time when very small variations in the storm’s track could lead to very large differences in outcome.

Imagine, for instance, that it’s 8:00 PM Saturday, and Isaac is hugging the coast of Cuba at the spot presently forecast by the NHC:

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At that point, Isaac would likely be a weak hurricane or strong tropical storm, having strengthened somewhat Thursday and Friday but then weakened due to interaction with Hispaniola and eastern Cuba. It would be poised to weaken further, maybe to a middling tropical storm, as it moves west over or near Cuba. So we’d be talking about a weakening storm (weakening temporarily…probably), with an uncertain track, triggering potential widespread and politically charged evacuations.

Note that I said “over or near Cuba.” That’s a hugely important distinction. The exact path will matter a lot, both to Isaac’s ultimate U.S. landfall location and its ultimate U.S. landfall intensity. But it may well be impossible to predict, as of Saturday evening, whether the storm’s center will remain a few miles inland over Cuba, or a few miles offshore. Even the best forecasters and computer models in the world are simply incapable of predicting hurricanes with that level of detail — but in this case, because of the angle and proximity to land, those tiny, detailed differences can potentially make an enormous difference. Hurricanes, of course, thrive over water, but wilt over land. So a wobble of a few dozen miles in either direction can literally change the course of history.

From that 8:00 PM Saturday point, all kinds of wildly divergent possibilities would still be very much alive. Isaac would still be capable of weakening tremendously over Cuba with a slight jog west, emerging over the Gulf as a far more disorganized system than expected, and winding up passing well west of Tampa with perhaps just tropical storm force winds. Conversely, it would also still be capable of popping off Cuba earlier than expected, weakening less than forecast, quickly rebuilding its strength, and making a beeline for Florida’s west coast as it rapidly intensifies, maybe becoming a major hurricane en route to the Tampa area or elsewhere.

Faced with such a wide array of scenarios, what would prudent disaster planners do? Assume the worst, of course. But that always carries the risk of being myopically accused, with 20/20 hindsight, of “overhype” when the worst-case scenario doesn’t materialize, as I’ve written before. And the risk of such accusations is even higher in this case, with such a politically charged decision as how to handle the RNC — a decision possibly being made by a Democrat, no less!

I don’t know exactly how long it takes to evacuate vulnerable areas in and near Tampa, but it’s a highly flood-prone city, and so I assume Saturday afternoon/night would be prudent, perhaps Sunday morning at the absolute latest, if a potential Monday-evening landfall is anticipated (with conditions already worsening by early Monday). I would also assume that it’ll be necessary to make a call about such a massive event as the RNC as early as possible, given the logistics involved, and the need to avoid adding to the burden of local law enforcement, traffic management and so forth, if a evacuation of locals is anticipated. All in all, it seems highly plausible to me that a decision would need to be made sometime on Saturday.

And it seems equally plausible that, by Saturday, anything from a Category 3 hurricane directly slamming Tampa to a tropical storm passing well offshore will remain viable possibilities.

If so, and if Mayor Buckhorn cancels the RNC and orders evacuations because of the worst-case scenario, I hope he won’t be raked over the coals and accused of naked partisanship if the best-case scenario occurs instead. I also suspect that hope is entirely in vain.