After causing “huge,” “terrible” damage overnight in the Turks and Caicos Islands, Hurricane Ike is holding steady at 135 mph, with a pressure of 949 mb, and its eye is now parked directly over Great Inagua in the Bahamas:
“Rainbow” infrared satellite view at 11:45 AM EDT. Live loop here.
Ike is continuing west toward Cuba, where it is expected to make landfall tonight. The official forecast track has Ike traversing almost the entire island from east to west, which would greatly weaken the storm, but would also, in Alan Sullivan‘s words, “cause massive devastation. Cuba is accustomed to hurricances, but rarely have I seen such an ominous looking onset. A large part of the country could be ravaged, including Havana.” Will Castro’s government again claim “no casualties,” as they rather implausibly did with Gustav, and again refuse international aid, a la the Burmese junta?
Ike could be somewhat less of a disaster for Cuba if it takes a slightly different course — for instance, “bouncing” off the coast and taking its WNW turn a little sooner than expected, tracing the north shore, which would keep the right-front quadrant over water — and this is entirely possible. Cuba is a long, narrow island, so a tiny “wobble” could have a huge impact. Such a lucky event for Cuba would be unlucky for the U.S., however, as it would keep Ike stronger as it approaches the Gulf of Mexico. As the National Hurricane Center’s 11am EDT discussion puts it:
ONCE INLAND…WEAKENING IS EXPECTED BUT THE DEGREE OF WEAKENING DEPENDS ON HOW LONG THE CENTER REMAINS INLAND. THE LATEST OFFICIAL FORECAST KEEPS IKE INLAND FOR APPROXIMATELY 36 HOURS SO SIGNIFICANT WEAKENING [TO A MINIMAL HURRICNAE] IS SHOWN. HOWEVER…ONLY A SMALL DEVIATION FROM THE FORECAST TRACK COULD RESULT IN THE CENTER OF IKE MOVING BACK OVER WATER SOONER.
Also, if Ike deviates a bit north of the current track (as opposed to south, which is also possible), Key West would be back in the bullseye. This could happen with little warning, which is why Sullivan continues to urge his fellow Floridians in the Keys to get the hell out:
I must remind residents of Key West that several models only brush the storm along the Cuban coast, retaining plenty of punch for the lower Keys. One outlier still brings Ike through the Florida Straits without Cuban landfall, and runs the storm directly over Key West. The scenario cannot be ruled out! If it occurs, Key West will be completely overwashed. I know you Conchs are a tough and prideful bunch, but what’s so great about dying like a damn fool because you didn’t take the Big One seriously? Leave today!
After Cuba (and perhaps the Keys) comes of Gulf of Mexico. Once Ike exits Cuba — whenever and wherever, exactly, that happens — and re-emerges over water, re-strengthening is expected. The Gulf of Mexico is still warm (in spite of moderate upwelling caused by Gustav), and, crucially, wind shear is expected to be low (though that, too, could change).
Moreover, the current forecast takes Ike directly over the Loop Current, which could fuel rapid re-intensification. And, as the Houston Chronicle‘s Eric Berger explains, we can’t count on Gustav Redux in this regard:
[T]here’s a reasonable chance a storm coming off Cuba would pass over the Loop Current, allowing for significant and rapid re-intensification.
But wait, didn’t forecasters say that about Hurricane Gustav? Yes, the forecasters predicted that. What they didn’t foresee was slightly higher than anticipated shear as Gustav crossed Cuba, which caused the storm’s vortex — it’s central tower — to become off-centered.
This could also happen with Ike, but we just cannot know at this time. Wind shear isn’t forecast to be a significant impediment in three to five days time, but such forecasts aren’t wholly reliable.
There are other potential mitigating factors in the Gulf, too. As noted by the forecasters at the Houston/Galveston office of the National Weather Service, one is the potential to encounter dry air along the Gulf Coast like that which has kept our recent mornings most pleasant. An incursion of dry air could also disrupt Ike’s circulation.
All right, so Ike is headed for the Gulf of Mexico, with the potential to be a major hurricane — either because of less-than-forecast weakening over Cuba (due to a slight course variation) or because of rapid re-strengthening, or both. But where will it go? Isn’t that the million-dollar question.
Of course, we’re talking about a 5-7 day forecast, so it’s impossible to say with any precision. As the NHC discussion says, “IT IS MUCH TOO EARLY TO ANTICIPATE WHICH AREAS ALONG THE GULF COAST COULD BE IMPACTED BY THIS SYSTEM.” Anyone from Tampico to Tampa Bay could potentially be at risk. “From Corpus Christi to the Louisiana-Mississippi border remain the likeliest landfall locations,” according to Berger.
Extrapolating from the forecast track and the computer models, the current “bullseye” would appear to be somewhere between Houston/Galveston and the Texas/Louisiana border region. But that can, and probably will, change. (Case in point: just over 48 hours ago, Miami appeared to be in the bullseye; 24 hours ago, New Orleans did.) All anyone can really say at this point is, stay tuned.
Incidentally, Ike is now officially the only active storm left in the Atlantic basin. Josephine was downgraded to a remnant low yesterday, and the final advisory on Hanna — which proved, as expected, to be “little more than a windy rainstorm” for the East Coast — was issued at 5:00 this morning. Hanna’s extratropical remnant is now over Atlantic Canada, speeding northeastward. So Ike is now the only game in town. Moreover, Sullivan thinks Ike may be the last blockbuster storm of the season: “Fall is deepening prematurely. We will not see many more Cape Verde storms. Hanna’s remnant, caught in the polar jet, has rocketed all the way to Nova Scotia in the last few hours. Hurricane season has peaked. Once we’re done with Ike, things will be quieter.” We shall see.
P.S. In comments yesterday, a couple of questions:
Technical query: I often hear that warm waters power hurricanes. Does this mean that hurricanes cool the waters they pass over, so that another hurricane following too closely will typically be at a disadvantage?
and
I do not understand completely how a “lode of dry air” and a high pressure system affects a hurricane. Is this information available somewhere, hopefully in short form and non technical language.
I’ll start with the first question. Hurricanes do indeed tend to cool the waters they’re over, particularly if they move slowly or stall over those waters, due to “upwelling” — the winds dredge up cooler waters from beneath the surface. However, this has far less impact on areas, like the Loop Current, with a very high Tropical Cyclone Heat Potential, meaning the warm water is deep — in other words, there isn’t as much cool water under the surface to “upwell”!
With regard to Question #2: “dry air” is damaging to a tropical cyclone because these systems depend on moist air to power ther development. If a patch of dry air gets sucked into the circulation of a hurricane, it can cause significant short-term weakening. If a continuous stream of dry air is getting “entrained” into the storm’s core, the effect can be longer-lasting.
As for the high-pressure: in the post that spawned those comments, I had referenced an upper-level high pressure system that is steering Ike. (“Upper-level” meaning higher up in the atmosphere.) That is a key role of high-pressure systems vis a vis hurricanes: they tend to steer storms around their clockwise rotation, which generally means east to west in the Northern Hemisphere. (A “weakness” in the high can result in the storm moving more north. I like to think of high pressure as pushing hurricanes, whereas troughs of low pressure pull them.)
Another key role of upper-level high-pressure systems is in promoting a hurricane’s “outflow,” and thus helping to strengthen it. If an upper-level high-pressure system parks directly over the hurricane (which is itself a lower-level low-pressure system), this promotes healthy “outflow” of air from the hurricane into the surrounding environment, and leads to intensification. (By contrast, if an upper-level low-pressure system gets too close to a hurricane, it will cause “wind shear” and weaken the storm.)
A good source for reasonably non-technical explanations of lots of hurricane questions is the NOAA Hurricane FAQ.
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