11 September 2008

Ike now a serious threat to the entire Gulf coast...

As of 15Z today, Ike was still an 85kt CAT2 hurricane (945mb), but the feature that is becoming very disconcerting is the SIZE of the storm (defined as the radius of the wind field).  Tropical storm force winds should be affecting nearly all of LA and TX coasts within a couple days.  Right now, hurricane force winds extend out 100 miles to the north and east of the center.  A hurricane warning is already in effect for much of the TX and LA coasts, and Galveston and Houston have begun evacuating.  Landfall is expected just south of Houston in the early morning hours on Saturday as a CAT3 hurricane.  There is a substantial risk for storm surge flooding now through Saturday from Brownsville to Mobile, with the highest risk centered on Galveston Bay.  Ike is already more powerful than Katrina or Rita, as measured by its kinetic energy and potential for storm surge.

Storm surge is influenced by five primary factors: storm size, storm translation speed, storm direction, storm intensity, and bathymetry.  All five are working against the western and northern Gulf coast now, most notably the northern Texas coast, which is at extreme risk.
Ike is a strong storm, and still gradually getting stronger... it's also a large storm, and gradually getting larger.  It is moving slowly, and in a straight line (no curves in the track), and the Gulf coast has an extensive continental shelf offshore.  These all combine to produce an enormous storm surge over a large stretch of coastline.

The Navy has a model that predicts significant wave heights (individual waves could be twice as high as the sig wave ht):

The NHC produces a graphic showing the probability of a 5' or greater storm surge:

The maximum potential surge height is shown at:

And NHC runs a sophisticated storm surge model called SLOSH which accounts for storm motion, bathymetry, topography, etc... a worst-case scenario for a CAT3 Galveston Bay landfall can be found here:

Please visit my tropical Atlantic headquarters.

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