Subtropical Storm ANDREA

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SUBTROPICAL STORM ANDREA DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL012007
500 AM EDT THU MAY 10 2007
 
ANDREA CONTINUES TO APPEAR RATHER UNIMPRESSIVE...WITH LATEST
SATELLITE IMAGERY AND RADAR INDICATING SOME WEAK PULSATING
CONVECTION TO THE EAST OF THE CENTER WHILE THE WESTERN HALF REMAINS
NEARLY CONVECTION FREE.  SATELLITE INTENSITY ESTIMATES HAVE
DECREASED TO 25 TO 30 KNOTS...AND THE INITIAL INTENSITY HAS BEEN
ADJUSTED DOWNWARD CONSERVATIVELY TO 35 KT.  AN AIR FORCE
RECONNAISSANCE AIRCRAFT IS SCHEDULED TO INVESTIGATE THE SYSTEM
LATER THIS MORNING TO PROVIDE A BETTER ESTIMATE OF THE INTENSITY.
 
WATER VAPOR IMAGERY DEPICTS VERY DRY AIR SURROUNDING THE CYCLONE IN
ALL QUADRANTS EXPECT FOR THE NORTH.  LATEST SHEAR ANALYSIS FROM
CIMSS SHOWS 20 KNOTS OF NORTHWEST SHEAR IMPINGING UPON THE CYCLONE.
THIS COMBINATION OF SHEAR AND DRY AIR IS INHIBITING CONVECTION AND
DISPLACING THE CONVECTION THAT DOES EXIST TO THE EAST OF THE
CENTER. BOTH THE SHIPS AND GFDL GUIDANCE SUGGEST POSSIBLE
STRENGTHENING.  HOWEVER GIVEN THE CURRENT NORTHWESTERLY SHEAR AND
THE ABUNDANCE OF DRY AIR...THE OFFICIAL FORECAST CALLS FOR GRADUAL
WEAKENING AND DISSIPATION IN 96 HOURS...IF NOT SOONER.  THERE IS A
CAVEAT TO THE INTENSITY FORECAST...IN THAT A MID- TO UPPER-LEVEL
LOW CURRENTLY OVER TEXAS MAY INTERACT WITH ANDREA IN 72 HOURS.
 
THE CYCLONE HAS DRIFTED SLIGHTLY TO THE SOUTHWEST...AS A RESULT OF
BEING EMBEDDED IN A LARGE DEEP-LAYER TROUGH.  THE TRACK FORECAST IS
A BIT COMPLEX.  MOST OF THE MODEL GUIDANCE TAKES THE CYCLONE
GENERALLY SOUTHWARD OVER THE NEXT TWO TO THREE DAYS...AS THE
UPPER-LEVEL TROUGH THAT THE SYSTEM IS CURRENTLY EMBEDDED IN OPENS
UP AND MOVES EASTWARD...AND THE LOW-LEVEL STEERING REMAINS WEAK. IF
ANDREA STILL EXISTS AFTER 72 HOURS...THE UKMET...GFS...AND ECMWF
FORECASTS A FRONT EXITING THE EASTERN U.S. PUSHING THE DISSIPATING
CYCLONE EASTWARD.
 
GIVEN THE UNCERTAINTIES IN THE FORECAST TRACK AND INTENSITY...THE
TROPICAL STORM WATCH REMAINS UNCHANGED AT THIS TIME.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      10/0900Z 30.4N  80.0W    35 KT
 12HR VT     10/1800Z 30.2N  80.1W    30 KT
 24HR VT     11/0600Z 29.9N  80.2W    30 KT
 36HR VT     11/1800Z 29.7N  80.2W    25 KT
 48HR VT     12/0600Z 29.5N  80.1W    25 KT
 72HR VT     13/0600Z 29.3N  79.9W    25 KT...DISSIPATING
 96HR VT     14/0600Z...DISSIPATED
 
$$
FORECASTER MAINELLI
 
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