Visible satellite view of Ike at 10:15 AM EDT. Live loop here.
Dr. Jeff Masters, in a hot-off-the-presses post, paints a frightening picture of Ike’s storm-surge potential:
Hurricane Ike’s winds remain at Category 2 strength, but Ike is a freak storm with extreme destructive storm surge potential. . . . Ike is now larger than Katrina was, both in its radius of tropical storm force winds–275 miles–and in it radius of hurricane force winds–115 miles. For comparison, Katrina’s tropical storm and hurricane force winds extended out 230 and 105 miles, respectively. Ike’s huge wind field has put an extraordinarily large volume of ocean water in motion. When this swirling column of water hits the shallow waters of the Continental Shelf, it will be be forced up into a large storm surge . . . Ike will probably inundate a 180-mile stretch of Texas coast from Port O’Connor to just north of Galveston with a 10-15 foot storm surge. This will occur even if Ike is a Category 1 storm at landfall. . . .
The amount of water Ike has put in motion is about 50% greater than what Katrina did, and thus we can expect Ike’s storm surge damage will be similar to or greater than Katrina’s. The way we can estimate this damage potential is to compute the total energy of Ike’s surface winds (kinetic energy). To do this, we must look at how strong the winds are, and factor in the areal coverage of these winds. Thus, we compute the Integrated Kinetic Energy (IKE) by squaring the velocity of the wind and summing over all regions of the hurricane with tropical storm force winds or higher. This “Integrated Kinetic Energy” was recently proposed by Dr. Mark Powell of NOAA’s Hurricane Research Division as a better measure of the destructive power of a hurricane’s storm surge than the usual Category 1-5 Saffir-Simpson scale. For example, Hurricane Katrina hit Mississippi as a strong Category 3 hurricane, yet its storm surge was more characteristic of a Category 5 storm. Dr. Powell came up with a new scale to rate potential storm surge damage based on IKE (not to be confused with Hurricane Ike!) The new scale ranges from 1-6. Katrina and Wilma at their peaks both earned a 5.1 on this scale (Figure 2). At 9:30am EDT this morning, Ike earned a 5.6 on this scale, the highest kinetic energy of any Atlantic storm in the past 40 years.
Masters’s post is, to me at least, a little confusing at first blush, because he says Ike’s “maximum surge is not likely to reach the extreme values above 20 feet seen in Hurricane Carla” — but then he talks about Ike’s surge damage being “similar to or greater than Katrina’s” record-setting surge! But I think this apparent discrepancy is explained by the size issue. What Masters is saying, if I understand him correctly, is not that Ike’s storm surge in any single location will approach or exceed Katrina’s stunning height (which approached 30 feet) or level of devastation, but rather that the total “storm surge damage,” across the entire region combined, will be higher, because a slightly lower (but still very severe) surge will be spread out over a wider area.
Add in the Texas coast’s unusual vulnerability to storm surge, and this looks to me like a real potential calamity, if Dr. Masters is right. And he’s got charts & graphs to back him up. Here’s that “Integrated Kinetic Energy” thingy — a.k.a. “Ike’s IKE” — comparing Ike to various historical storms, including Katrina:
On the other hand, one wonders what wind-speed values the IKE calculation is using, and thus what impact the “relatively little transport of winds aloft down to the surface” may have on this calculation. Recall that the NHC’s current official maximum surface wind value — 100 mph — is, concededly, probably overstated at the moment.
That’s probably a quibble, though: the basic premise of Masters’s argument seems sound, to me at least. Which leads to FlyOnTheWall’s excellent comment. He summarizes Masters’s post as follows:
In other words, the best case scenario is that Ike continues to confound expectations, remains a surface-level Category 1 hurricane (which it effectively is right now), and hits Texas with a storm surge of the sort that might ordinarily be generated by a Cat 4-5. Or, to be more precise, without the narrow peak a Cat 4-5 would generate just east of its eye, but with an even broader swath of serious flooding. The worst case scenario is that Ike confounds expectations by tying together its upper and lower circulation, its eyewall gets replaced, and it suddenly strengthens into a truly major hurricane — bringing incredibly destructive winds on top of the storm surge.
Listening to the emergency responders in the Houston metro area, I’m struck that they’re largely focused on the potential for the worst-case scenario. That is, they seem to be worried about shifts in the track and the strength of the winds. It’s now virtually certain that Galveston island will be flooded from the bay-side; and it’s not outside the realm of possibility that the surge will exceed the height of the floodwall, too. You’d think that, after Katrina, they might have figured out that the intensity at landfall matters a whole heck of a lot less than the width of the field and the resultant surge. Perhaps Ike will make them pay attention to the IKE.
Alan Sullivan, for his part, offers an additional reason to be concerned about the surge, while mildly pooh-poohing Masters’s premise:
I am concerned about surge. Because the storm is so broad, [Masters’s predicted] heights may be a bit melodramatic, but the duration of the event troubles me.
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.
P.S. Meanwhile, in comments and on his blog, Sullivan elaborates on the inland tornado and wind threat:
Ike has the potential to be unusually nasty inland. It is so big that the circulation will survive for some time. I expect a lot of tornadoes, and they could occur all the way to Oklahoma. . . . Tornado risk will be highest along the track of the core, and also in squall bands to the east. There may be heavy rains and tropical storm winds in some bands west of south of the center, as the storm moves inland, but those are much less likely to be tornadic. . . .
The combination of heavy rain and prolonged wind will make large trees extra vulnerable. Trees that could tolerate a quick blast may collapse when hit by a fourth hurricane-force squall after six inches of rain. Expect serious tree damage, blocked streets, power lines torn, crushed cars and mobile homes — all in much higher degree than would be usual in a landfalling category one or two hurricane. Even on high ground and well inland, mobile home residents should seek shelter this time.
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