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Ike strengthens slightly, wobbles west; storm surge begins

September 12th, 2008 - 7:18 am

[NOTE: The Houston Chronicle's Eric Berger will be hosting a live chat on Hurricane Ike at 3:00 PM EDT today. His chats are always excellent.

Also, Dr. Jeff Masters has a new post up. His lede sentence: "Hurricane Ike is closing in on Texas, and stands poised to become one of the most damaging hurricanes of all time." Read the whole thing.]

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Ike’s winds strengthened slightly overnight, to 105 mph, and the National Hurricane Center is now once again predicting a “major hurricane” at landfall — minimal Cat. 3 instead of maximal Cat. 2. [UPDATE, 11:00 AM: Or not.] But some folks in the media area are focusing way too much on this distinction. The difference between 110 mph and 115 mph winds is negligible, and the Saffir-Simpson Scale is a poor indicator of storm surge potential.

Even if Ike’s winds were to unexpectedly weaken to Cat. 1 force (or, heck, to tropical storm force), Ike would still be a “major hurricane” in terms of its massive storm surge. The surge, not the category, is the story! This is because of the sheer volume of water Ike is pushing across the Gulf, as I discussed at length yesterday. And that water is already in motion, inexorably bearing down on the gently sloping Texas coast. If coastal residents are taking this storm less seriously than they might because it’s “only” a Category 2, they are making a serious mistake. Eric Berger has an excellent post this morning about the predicted surge, with an updated SLOSH map.

In fact, the storm surge has already begun. In comments, Shreela (who will be live-Twittering the storm from Houston) wrote earlier this morning: “Most coastal people have evac’d already, and now the surge has covered some roads too much to evac from some locations. Since the evac was mandatory, rescue personal is relieved of any liability of those that chose not to eac.” That’s right — almost 18 hours before landfall, and the storm surge is already underway. As AccuWeather’s Jesse Farrell writes:

I’m really worried about the situation in Texas, with the video that I’m seeing on-air this morning. I mean, we’re seeing the water level near the top of the sea-walls and piers being destroyed already, and the storm’s 230 miles away — it’s not even cloudy on the coast yet! It’s an eerie and foreboding situation.

Eerie and foreboding, but perhaps not surprising, since Ike has already caused flooding in such faraway locales as Pensacola. I can’t say it enough: this is going to be a very severe storm surge event!!

[UPDATE, 12:57 PM EDT: Lou Minatti notes that the Galveston Strand is already flooding! You can see for yourself on the Galveston webcam page.]

You can watch the surge’s progress live, via NOAA’s tidal gauges. I find the Texas station map particularly helpful in locating the relevant stations to check. For example, here’s the plot for the Galveston Bay Entrance North Jetty:

northjetty-friam.png
Tidal gauge at 9:36 AM EDT. Live data here.

[UPDATE: That tidal link seems not to be working, for some reason. Here's one that is, and here's its live data plot.

(If you've visited this page multiple times, you may need to hit your browser's "Reload" or "Refresh" button to view the latest image below. Note that times are in GMT, which is 4 hours ahead of EDT. So, for example, "16:00" on the chart is 12:00 noon EDT, and 11:00 AM Houston time.)

]

As you can see, the surge began with this morning’s high tide, and is continuing to steadily climb, even as the predicted tide (the blue line) is supposed to be going out somewhat. Today’s bigger “low tide,” this evening, won’t be very “low” at all — water will just keep piling in — and then things will get really bad as the tide begins to come back in, along with the center of the storm, overnight.

Recall what Alan Sullivan wrote about Isabel, another storm with a geographically huge swath of winds and surge:

Isabel caused record flooding in the upper Chesapeake (and it had weakened to tropical storm) because it was big and slow moving enough to pile three successive high tides into the mouth of the bay, and not let them out again. Weather was improving and residents thought the storm was over when the final surge broke all records.

Ike is not expected to linger, so that, at least, is a blessing. But it’s so big that “successive high tides” will still be a problem.

The one major question mark remains Ike’s track, and specifically, whether it will make landfall up the coast, or down the coast, from Galveston Bay. The surge will be significantly lower if the center comes ashore just to Galveston’s northeast, keeping the “right-front quadrant” away from the bay. Residents therefore need to hope for northward, not westward, wobbles in Ike’s track. Unfortunately, the 5am EDT discussion stated: “IKE WOBBLED A LITTLE WESTWARD DURING THE PAST SEVERAL HOURS…BUT APPEARS TO HAVE RESUMED A MOTION OF 290/11.”

The satellite loop shows that Ike has indeed resumed its expected course (click “Trop Fcst Pts” to see the forecast track), but the westward wobble overnight already resulted in a tiny southward “bump” in the expected landfall point, as of the 5am forecast track. It was a very slight change, but it’s still a change in the opposite direction from what folks in the Galveston Bay area want to see. In Berger’s words:

A more northward turn, which might spare . . . Galveston Island a catastrophic storm surge, has not yet happened. And with landfall due to occur in less than 18 hours, time is running out.

P.S. As the SLOSH surge map shows, the Port Arthur area is actually expected to get the worst of Ike’s surge on the current track, even though the center is forecast to hit Galveston Island. This is a consequence of Ike’s strange structure. (As Alan Sullivan says, “The wind maximum remains far removed from the center, and there is no real eye.”)

Don’t get me wrong, the surge will still be catastrophic in Galveston Bay on this track — we’re talking about the difference between 18-22 feet (in Galveston Bay) and 22-24 feet (near Port Arthur), so it’ll be bad in both places — but let’s not neglect the folks in the Port Arthur region (and, for that matter, in low-lying southwestern Louisiana), who will take a severe blow, but are likely to be completely overshadowed by whatever happens in Houston/Galveston.

P.P.S. Sullivan, incidentally, dissents somewhat from the projections:

Extreme surge scenarios are being propounded for this storm. I suspect we will learn that they are excessive. Ike is too broad and weak to follow models based on the tight core structure of a normal hurricane. The danger will arise not so much from the height and speed of surge; but from its duration, and the immense wave heights built in the huge storm. I do not believe any location will be as severely affected as Mobile Bay in Katrina, where surge heights really did exceed twenty feet. But the lesser surge of Ike will be spread along a much greater length of coast. It will be very destructive.

Analogy: The elevation of ocean surface resembles a pimple in a typical hurricane. Ike’s deformation of the sea will resemble a hive — broader and flatter.

P.P.P.S. Houblog is blogging from the Houston area. If you know of other folks with regularly-updated liveblogs, let me know! [UPDATE: Dr. Melissa Clouthier will be liveblogging, and live-Tweeting, too.]

UPDATE: Earlier, in a “programming note,” I mentioned that I was scheduled to appear on George Putnam’s syndicated radio show, “Talk Back,” at 3:20 PM EDT today, to talk about Ike. However, sadly, George Putnam died this morning, and the interview has been canceled. Guest-host Chuck Wilder will be devoting today’s broadcast to a tribute to Mr. Putnam, who was 92. R.I.P., George Putnam.

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