Weather Nerd

Nagin orders mandatory evacuation, says "you need to be scared"

The Houston Chronicle‘s Eric Berger is looking at the 8pm EDT computer model runs, and he has some bad news for New Orleans:

I … expect the official track to be nudged slightly eastward toward New Orleans [at 11pm EDT] tonight. This raises the likelihood of the [“worse than Katrina”] New Orleans surge scenario I laid out below, but it’s by no means a certainty.

However, it’s not looking good.

Mayor Nagin must be looking at the same data, given his rhetoric in ordering a mandatory evacuation:

Mayor Ray Nagin late Saturday warned that Gustav is the “mother of all storms” and ordered a mandatory evacuation for the West Bank of New Orleans for 8 a.m. Sunday and noon for the East Bank.

“We want 100 percent evacuation,” said Nagin. “It has the potential to impact every area” . . .

“This is worse than a Betsy, worse than a Katrina,” Nagin said.

The mayor speculated that Gustav is so fierce Baton Rouge likely will experience 100 mph winds.

“You need to be scared and you need to get your butts out of New Orleans right now,” Nagin said.

Nagin said he expects Gustav to “punch holes in the Harvey Canal,” which will cause the West Bank to become a bath tub.

The West Bank has 8-foot-high to 10-foot-high protection, he said. Gustav’s storm surge may be 15-, to 18- to 24-feet high.

Anyone who opts to remain in New Orleans “will be on your own,” Nagin warned, adding that services will not be available.

Needless to say, I agree with the decision to evacuate. However, I think Nagin is actually going a bit overboard with his rhetoric here, perhaps overcompensating for his Katrina failures. More on that a little later.

One thing Nagin’s right about, for sure, is that New Orleans residents need to be scared — at least scared enough to, as the mayor said, get their butts out of New Orleans right now. One reason to be scared is that Gustav is actually accelerating, which is very bad news. As Alan Sullivan writes:

Forward speed has increased to 15 mph, and the steering current has really steadied. As I watch the time-lapse imagery, I can see that Gustav has settled into alignment with the other weather systems in the region, and it will probably not deviate from its present track before Gulf Coast landfall. Because it is moving faster than previous projections suggested, it will bring more of its force to the coast.

While Gustav wavered in the Caribbean, bouncing from island to island, I was hopeful that it would not reach the US as a major hurricane. Worst case scenarios rarely come to pass. First Gustav would have to escape the bind of other weather systems and mountainous terrain; then it would have to spin through a rapid intensification phase south of Cuba; finally it would have to find a strong steering current that would bear it swiftly across the Gulf before shear or cooling waters could weaken it. All these things have happened. Now it is just a question of where the eye goes ashore.

If landfall occurs near Atchafalaya Bay or further west, the eyewall will pass safely SW of New Orleans. In that case conditions at the city should not severe enough to breach major levees, unless they are weaker than they were before Katrina. But if landfall occurs near Grand Isle, then New Orleans will be hammered by the northeast quadrant of the storm — the strongest part.

That would the worst-case scenario, and indeed, the true “mother of all storms.”

But it’s only one scenario, and that’s where I think Nagin’s rhetoric is a bit overheated. Gustav may be worse than Betsy and Katrina, but that remains to be seen; it all depends on the track, how much the storm strengthens tomorrow morning and afternoon, and how much it weakens tomorrow night and Monday before landfall. Residents definitely need to know that it could be worse than Betsy and Katrina, you don’t want to tell people it’s definitely going to be worse than those storms, lest your overconfident forecast fail to verify, and you become the “boy who cried wolf” — unable to motivate people to leave the next time a potential “mother of all storms” threatens.

Moreover, Nagin made one statement that makes no sense whatsoever to me, which I edited out of my earlier blockquote because I think it’s just flat incorrect. According to the Times-Picayune paraphrase, Nagin said “Katrina had a footprint of about 400 miles … [whereas] Gustav is about 900 miles and growing.” As far as I can tell, that’s simply not true. According to the NHC, Gustav’s tropical-storm force winds extend a maximum of 170 miles out from the center, on the northeast side; on other sides, the boundary is about 140 or 85 miles. You could say it has a 300-mile “footprint,” perhaps a bit more if you include peripheral effects outside the sustained tropical-storm-force area — but certainly not 900 miles, which is roughly the width of the entire Gulf of Mexico from Texas to Florida!

And while Gustav is indeed growing, it’s not bigger than Katrina, at least not yet — and there’s no possible way it will ever be more than twice Katrina’s size. I don’t even think that’s physically possible at the Gulf’s latitude.