16 September 2003

Isabel weakens in the face of shear...

During the past 24 hours, Isabel has encountered fairly significant
vertical wind shear, on the order of 20kts from the southwest.  This is
very evident in satellite imagery.  SSTs under the storm continue to be
plenty warm at about 29C, but her slow forward motion could be
responsible for some degree of upwelling.  She's also been ingesting
some drier air from the western side which has snuffed convection out a

At 15Z today, Hurricane Isabel was located at 27.4N 71.2W and tracking
NNW at 7kts.  Intensity has dropped quite a bit to 90kts and 959mb,
making her a CAT2 storm.  That is still a strong hurricane, but there's
the possibility that she COULD reintensify before landfall if the shear
lets up at all.  The hurricane-force winds extend 80 miles on the
northwest quadrant, so the exact location of where the eyewall makes
landfall is not so important; it's a large storm.

A Hurricane Watch has been issued for a large stretch of the Atlantic
seaboard, from Little River Inlet, SC to Chincoteague, VA.  These
watches will probably be upgraded to warnings at the 21Z advisory today
or 03Z tomorrow.  Precautions are already being completed, such as
moving ships out to sea to avoid being battered at port, coastal
evacuations, inland shelters being established and manned, and
positioning of emergency managers, utility repair workers, and Red Cross
personnel.  It's likely that many more evacuations will be made
mandatory by Wednesday morning.  Although Isabel has weakened a bit
recently, she still poses a very significant threat, in terms of winds,
storm surge, high surf, and rainfall.

NHC's forecast places landfall near Cape Lookout, NC on Thursday
mid-morning, then tracking inland over central VA and PA.  The passage
over VA is expected early Friday morning, and then midday Friday for

Please visit my tropical Atlantic headquarters.

P.S.  The aircraft reconaissance data that we enjoy so much is something
we shouldn't take for granted.  First of all, the Atlantic basin is the
only one in the world with routine recon flights, thanks to both NOAA
and the US Air Force.  And this past Sunday, for the first time since
1989, there was a close call which thankfully didn't result in an
accident.  As Pete Black of the NHC describes, "While climbing back to
altitude on Sunday after the second stepped descent, less than a minute
after the 200 ft run, the inboard engine on the right side flamed out
with two small exhaust explosions, and had to be shut down. Thank God
the aircraft was back to 1500 ft at the time and that it was late in the
flight, as the aircraft was able to continue climbing to safe altitude
and return to St Croix, where they were greeted by the airport fire
department lining the field after the aircraft commander declared an
emergency."  The plane and all crew returned safely, but not without a
bit of a scare.

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