Subtropical Storm ANDREA

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SUBTROPICAL STORM ANDREA DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL012007
1100 AM EDT WED MAY 09 2007
 
AN AIR FORCE RECONNAISSANCE PLANE HAS BEEN INVESTIGATING THE LOW
PRESSURE SYSTEM OFF THE SOUTHEAST U.S. COAST SINCE EARLY THIS
MORNING.  THE INITIAL LEG OF THE MISSION WAS FLOWN AT 300 MB FROM
WEST TO EAST OVER THE CIRCULATION CENTER...AND SEVERAL DROPSONDES
WERE RELEASED.  THE TEMPERATURE PROFILES REVEAL A RATHER FLAT
THERMAL CROSS-SECTION...NOT INDICATING A DISCERNIBLE WARM OR COLD
CORE AT ANY VERTICAL LEVEL.  THE WIND PROFILES...HOWEVER...SHOW
WINDS INCREASING WITH HEIGHT IN THE WESTERN HALF OF THE CIRCULATION
AND DECREASING WITH HEIGHT IN THE EASTERN HALF.  GOES IMAGERY
INDICATES THAT...COMPARED TO YESTERDAY...THE THUNDERSTORM ACTIVITY
HAS CONSOLIDATED CLOSER TO THE CENTER...BUT PRIMARILY IN THE
EASTERN SEMICIRCLE.  THERE IS ALSO A SLIGHT HINT OF UPPER-LEVEL
OUTFLOW WHICH WAS COMPLETELY ABSENT YESTERDAY...BUT THE SYSTEM
REMAINS EMBEDDED WITHIN A LARGE DEEP-LAYER TROUGH.  ALSO...THE
RADIUS OF MAXIMUM WINDS HAS CONTRACTED FROM MORE THAN 100 N MI
YESTERDAY TO ABOUT 50-60 N MI THIS MORNING.  BASED ON THE HYBRID
STRUCTURE OF THE SYSTEM...ADVISORIES ARE BEING INITIATED ON
SUBTROPICAL STORM ANDREA.  THE 40 KT INITIAL INTENSITY IS BASED ON
AN EARLY MORNING QUIKSCAT PASS AND RECENT AIRCRAFT DATA FROM 850
MB.

THE INITIAL MOTION IS SLOW AND GENERALLY WESTWARD...ABOUT 270
DEGREES AT 4 KT.  SINCE ANDREA IS ESSENTIALLY TRAPPED WITHIN A
MIDDLE- TO UPPER-LEVEL TROUGH THAT THE DYNAMICAL MODELS FORECAST TO
NOT MOVE MUCH DURING THE NEXT FEW DAYS...ANDREA WILL PROBABLY
CONTINUE TO MOVE SLOWLY...BUT IN THE GENERAL DIRECTION OF THE
NORTHEAST FLORIDA COAST.  THE OFFICIAL FORECAST GENERALLY FOLLOWS
THE SCENARIO PAINTED BY ALL OF THE MODELS...TAKING THE SYSTEM
SLOWLY SOUTHWESTWARD AND THEN SOUTHWARD DURING THE NEXT 3 DAYS OR
SO.  NONE OF THE MODELS BRING ANDREA INLAND...AND NEITHER DOES THE
OFFICIAL FORECAST.  ANDREA IS CURRENTLY OVER SEA-SURFACE
TEMPERATURES OF NO MORE THAN ABOUT 25 CELSIUS...AND THEY WILL NOT
GET ANY WARMER ALONG THE FORECAST TRACK.  THEREFORE A SLOW
WEAKENING TREND IS ANTICIPATED AND THE OFFICIAL FORECAST SHOWS
DISSIPATION NEAR THE COAST IN LESS THAN FIVE DAYS.  HOWEVER...SINCE
ANDREA MIGHT BRING WINDS OF TROPICAL STORM FORCE TO THE COAST...A
TROPICAL STORM WATCH HAS BEEN ISSUED.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/1500Z 30.8N  79.3W    40 KT
 12HR VT     10/0000Z 30.6N  79.9W    40 KT
 24HR VT     10/1200Z 30.2N  80.6W    35 KT
 36HR VT     11/0000Z 29.8N  81.0W    35 KT
 48HR VT     11/1200Z 29.6N  81.0W    30 KT
 72HR VT     12/1200Z 29.5N  81.0W    25 KT
 96HR VT     13/1200Z 29.5N  81.0W    25 KT...DISSIPATING
120HR VT     14/1200Z...DISSIPATED
 
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FORECASTER KNABB
 
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