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New Orleans in peril
Posted by on Friday, August 26, 2005 at 1:57 pm

At the risk of being alarmist, we could be 3-4 days away from an unprecedented cataclysm that could kill as many as 100,000 people in New Orleans. Such a scenario is unlikely — the conditions would have be just right (or rather, just wrong) — but IMHO, it’s not nearly unlikely enough to feel good about things. If I were in New Orleans, I would seriously consider getting the hell out of dodge right now, just in case. Once the evacuation orders are issued, if it comes to that, it’ll inevitably be an absolute madhouse, despite officials’ best efforts. (More here.)

Some computer models are taking Katrina on a worst-case scenario track: almost due north over the marshlands and straight into the below-sea-level city, or just to its west. If the hurricane is strong enough — and Category 4 is looking more and more likely — that could very possibly “flood the bowl,” breaching the Lake Pontchartrain levees and “turn[ing] the city and the east bank of Jefferson Parish into a lake as much as 30 feet deep, fouled with chemicals and waste from ruined septic systems, businesses and homes… trap[ping] hundreds of thousands of people in buildings and in vehicles… [while] high winds and tornadoes…tear at everything left standing.” (Source.) And, even if evacuation orders are issued, lots of people won’t leave. Hence the prediction of between 25,000 and 100,000 deaths in a worst-case direct hit.

I, and everyone else, had the same fear when Ivan was approaching last September. That storm ultimately took a right-hand turn and hit near the Florida/Alabama border. Georges in 1998 was also a close call, but it, too, veered right at the last minute. Will Katrina do the same? Maybe, but increasingly the computer models are suggesting not. Note the distinct westward shift in the GFS model’s predicted landfall point between last night and this morning. And the GFS is not alone. According to Charles Fenwick at Eye of the Storm:

Every global model plus the GFDL shifted its track to the west its forecast to the west in its 12Z run. Forecasts are now in a fairly tight cluster between eastern Louisana and Mississippi.

While it is generally unwise to hop onto one run of the models as the gospel, it is meaningful when every model makes the same type of shift.

This definitely shifts the area of concern much further west than I had been figuring.

CAVEAT: Hurricane forecasting is an extremely inexact science, especially when we’re talking about what will happen in 72+ hours. Hence my statement that the New Orleans scenario is “unlikely.” It would be statistically unlikely even if the Big Easy were directly in the center of the NHC’s forecast track, because these things can, and usually do, change. That’s why the highest coastal strike probability percentages at this point are under 20%. Katrina is going to hit somewhere along the Gulf Coast, but the actual odds of her taking any particular track, even the most likely one, are still quite low, because there are just so many possibilities. But despite that fact, if New Orleans is anywhere near the center of the risk area, residents need to prepare as if there is a 100% chance of a direct hit, because the 90% chance it won’t happen isn’t going save their lives if the 10% chance it will happens to come true.

Anyway, it will be very interesting to see what the National Hurricane Center’s discussion at 4:00 PM EST says. Presumably this new computer-model guidance will cause them to shift the official forecast track substantially to the west. But how far west? And how long will they wait before issuing watches and warnings? Normally, watches go up approximately 48 hours before the leading edge of the storm is expected to hit, but I wonder whether the NHC might fudge that a bit, and issue watches earlier, if New Orleans looks like the target, in light of the time-consuming logistical nightmare that a citywide evacuation would be. On the other hand, an evacuation that ultimately proves to have been unnecessary is economically costly and, more importantly, may have a vigilance-lowering “boy who cried wolf” effect, especially since it would be the second time in as many years. So this is going to be a tough call for the NHC. Here’s hoping they get it right… and here’s praying that New Orleans is spared.




3 Comments on “New Orleans in peril”

  1. Charles Says:

    It will be reallllll bad.

    I have been in several floods in New Orleans. A Hurricane, again, will wipe the city clean off the map.

  2. Charles Fenwick Says:

    The report iskind of confusing. In the first paragraph it says the worst case is the storm coming in from due south of the city. But then it goes on to describe the effects caused by the storm being east of the city (and headed north).

    It kind of runs contrary to what I’ve always thought to be the threat… I thought the worst case would be water being pushed west up the mouth of the Mississippi, not water being pushed south along the Lake (as described here). It kind of surprises me that the Lake is large enough for there to be a fetch long enough to generate a surge.

    I suppose I am more ignorant of the subject than I had reasoned.

  3. Brendan Loy Says:

    I interpret it as meaning, almost due south, but east of the city such that, essentially, the western eyewall would be over the city.

    It’s also possible that the Times-Picayune reporter got it wrong. Either way, we just need to hope that the hurricane steers clear of New Orleans altogether.


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