Ike just keeps growing, but still not strengthening

The headline on the National Hurricane Center’s 11am EDT public advisory reads: “IKE CONTINUES TO GROW IN SIZE BUT HAS NOT STRENGTHENED YET.”

They’re not kidding about that “grow in size” thing. Check out Ike’s wind field 36 hours ago, versus Ike’s wind field now:

You can see this growth in animated form, using the NHC’s Surface Wind Field archive loop.

Meanwhile, here’s what the 11am discussion has to say about Ike’s current intensity and structure:

DATA FROM AIR FORCE AND NOAA AIRCRAFT INDICATE THAT IKE IS MAINTAINING AN ATYPICAL WIND STRUCTURE…CHARACTERIZED BY A VERY BROAD WIND FIELD WITH MULTIPLE WIND MAXIMA AND RELATIVELY LITTLE TRANSPORT OF WINDS ALOFT DOWN TO THE SURFACE. THE NOAA AIRCRAFT REPORTED MAXIMUM FLIGHT-LEVEL WINDS OF [119 MPH] 100 NMI NORTH-NORTHEAST OF THE CENTER…BUT SFMR AND DROPSONDE DATA INDICATE THAT THE SURFACE WINDS IN THAT AREA WERE ONLY AROUND [75 MPH]. IN FACT…THERE HAS BEEN NOTHING AT THE SURFACE RECENTLY THAT QUITE SUPPORTS THE CURRENT [100 MPH] ADVISORY INTENSITY.

To give you an idea, the usual formula for converting flight-level winds to surface winds is a multiple of 0.9, so you’d expect 119 mph flight-level winds to correspond roughly to 107 mph surface winds — not 75 mph! As I said before, Ike is truly a weird storm.

The NHC’s observation about “relatively little transport of winds aloft down to the surface” supports Alan Sullivan’s prediction that “I am not persuaded [the] tight core will be vigorous enough to bring maximum winds down to the surface when it arrives in the coastal zone.” That’s if the current structure doesn’t change, of course, which is a huge “if.”

It’s also worth noting that the NHC is now saying Ike has “multiple wind maxima,” not just “double.” I guess that means it has three eyewalls?! The second paragraph of the discussion also suggests this:

FORECASTING CHANGES IN THE WIND STRUCTURE OF TROPICAL CYCLONES IS EVEN MORE CHALLENGING THAN FORECASTING THE INTENSITY…BUT IKE HAS PLENTY OF TIME FOR ONE OF THE OUTER MAXIMA TO CONTRACT AND FOR THE WINDS TO TRY TO CATCH UP TO THE CENTRAL PRESSURE…CURRENTLY ABOUT 945 MB.  ALTHOUGH OUTFLOW CONTINUES TO BE RESTRICTED TO THE NORTHWEST…IT IS STRONG ELSEWHERE AND THE SHEAR IS EXPECTED TO REMAIN LIGHT.  ONE INHIBITING FACTOR COULD BE UPWELLING/MIXING OF COOLER WATER AHEAD OF THE PATH OF IKE DUE TO THE UNUSUALLY LARGE EXPANSE OF STRONG WINDS.  THE OBJECTIVE GUIDANCE NEAR LANDFALL RANGES FROM A CATEGORY FOUR FROM THE GFDL TO CATEGORY TWO FROM THE SHIPS MODEL…ABOUT THE ERROR ONE CAN EXPECT FROM AN OFFICIAL FORECAST ONE TO TWO DAYS OUT.  THE OFFICIAL FORECAST ROUGHLY SPLITS THE DIFFERENCE BETWEEN THESE GUIDANCE MODELS…AND ANTICIPATES THAT IKE WILL BE A MAJOR HURRICANE AT LANDFALL.

What a weird hurricane. The NHC really doesn’t know what to expect. But Texans should prepared for the possibility of a Cat. 4, just in case.

UPDATE: Eric Berger — who is currently experiencing a Drudgelanche — has much more on Ike. He will host a live chat at 3pm EDT.

Meanwhile, Alan Sullivan writes:

For several days weather observers have been remarking on the spread of the models, which resulted from differences in timing [the right-hand] turn.  At one extreme, recurvature would not commence until Ike was inland at the Rio Grande.  At the other, it would begin while Ike was still at sea, producing potential landfall locations all the way to the Louisiana-Texas border.

At this time the consensus suggests recurvature will begin near the coast and continue as the center moves inland.  Of course this is the trickiest scenario of all.  It means that the storm may be approaching middle Texas, at a safe distance from Houston, only to bend closer at the last minute and put the big city in the right front quadrant — the worst place.

I don’t blame Houston residents for worrying, and for treating the storm as though it were slamming the coast perpendicularly at high speed, with category four force.  But that is not going to happen.  The curving course and relatively slow forward motion (though it should accelerate some during recurvature) will allow a bit more time for land interaction, and Houston lies far enough inland that extreme winds can occur there only in direct, fast landfall.  Even if Ike tightens in proximity to land, its worst winds will be diminishing before it reaches the city.

However, I think Berger is a bit too casual about the rainfall potential of this very large system, and the double-flooding effect of prolonged onshore wind driving tidal surge to dam floodwaters from rainfall.  For Houston and many other places, flooding could prove the real menace of Ike. Get your property ready! And then go as local authorities direct.