Tropical Storm ALBERTO

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TROPICAL STORM ALBERTO DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL012012
500 PM EDT SUN MAY 20 2012
 
ALBERTO DOES NOT HAVE THE TYPICAL VERTICAL WIND PROFILE OF A HEALTHY
TROPICAL CYCLONE.  THE AIR FORCE PLANE THAT SAMPLED THE STORM ONLY
MEASURED MAXIMUM 850-MB FLIGHT-LEVEL WINDS OF 37 KT...YET SFMR
VALUES WERE AS HIGH AS ABOUT 50 KT.  THE SFMR ESTIMATES ARE LIKELY
TOO HIGH BASED ON COINCIDENT SPIKES IN THE RAIN RATE AND A
WELL-DOCUMENTED HIGH BIAS AT LOW-END TROPICAL STORM WIND SPEEDS. 
IN ADDITION...DROPSONDE DATA FROM THE AIRCRAFT DO NOT SUPPORT WINDS
OF 50 KT NEAR THE SURFACE.  THE INTENSITY IS THEREFORE BEING HELD
AT 40 KT.  THE AIRCRAFT DATA SUGGEST THAT THE BOUNDARY LAYER HAS
DECOUPLED...AND THE SURFACE CIRCULATION MAY NOW BE TAKING SOME TIME
TO SPIN DOWN.
 
ALBERTO IS INGESTING DRY AIR...AND IT HAS MOVED OVER SHELF WATERS
THAT ARE COLDER THAN 26C.  IN ADDITION...WESTERLY VERTICAL WIND
SHEAR IS EXPECTED TO INCREASE MARKEDLY DURING THE NEXT 24 HOURS. 
ALTHOUGH THE CYCLONE WILL TRAVERSE THE GULF STREAM AGAIN WHEN IT
ACCELERATES NORTHEASTWARD ON MONDAY...THE OTHERWISE HOSTILE
CONDITIONS SUGGEST THAT SIGNIFICANT INTENSIFICATION IS UNLIKELY. 
SMALL FLUCTUATIONS IN INTENSITY ARE POSSIBLE THROUGH TUESDAY
DEPENDING ON THE BEHAVIOR OF DEEP CONVECTION...BUT OVERALL LITTLE
CHANGE IN STRENGTH IS ANTICIPATED.  THIS SCENARIO IS SUPPORTED BY
THE BULK OF THE INTENSITY GUIDANCE.  ALBERTO COULD BECOME POST- 
TROPICAL BY WEDNESDAY AS IT MOVES TOWARDS EVEN COLDER WATER...WITH
DISSIPATION POSSIBLE BY THURSDAY.
 
THE MOTION HAS BECOME SOUTHWESTWARD DURING THE DAY...AND IT APPEARS
THAT ALBERTO IS BEGINNING ITS ANTICIPATED COUNTER-CLOCKWISE LOOP.
THE BLOCKING PATTERN IN PLACE OVER THE EASTERN U.S. IS STILL
EXPECTED TO BREAKDOWN THROUGH MONDAY...AND ALBERTO WILL RESPOND BY
ACCELERATING NORTHEASTWARD AHEAD OF AN APPROACHING LONGWAVE TROUGH.
THE 12Z ECMWF MODEL RUN...LIKE THE PREVIOUS ONE...IS STILL A LITTLE
SOUTH OF THE REST OF THE TRACK GUIDANCE ENVELOPE.  THE OFFICIAL
FORECAST IS CLOSE TO THE VARIOUS CONSENSUS MODELS THROUGH 48 HOURS
BUT A LITTLE FARTHER SOUTH AT 72 HOURS...HEDGING TOWARD THE ECMWF
SOLUTION.
 

FORECAST POSITIONS AND MAX WINDS
 
INIT  20/2100Z 30.9N  80.0W   40 KT  45 MPH
 12H  21/0600Z 30.8N  79.8W   40 KT  45 MPH
 24H  21/1800Z 31.2N  78.6W   40 KT  45 MPH
 36H  22/0600Z 32.5N  76.6W   40 KT  45 MPH
 48H  22/1800Z 34.7N  73.8W   40 KT  45 MPH
 72H  23/1800Z 38.0N  66.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  24/1800Z...DISSIPATED
 
$$
FORECASTER BERG
 
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