Tropical Storm ALVIN

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TROPICAL STORM ALVIN DISCUSSION NUMBER   9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP012007
800 PM PDT MON MAY 28 2007
 
THE CONVECTIVE PATTERN HAS BEEN FAIRLY STABLE FOR THE PAST SEVERAL
HOURS...WITH A SPOT OF -80C CLOUD TOPS PERSISTING SOUTH OF THE
ESTIMATED LOCATION OF THE LOW-LEVEL CENTER.  DVORAK INTENSITY
ESTIMATES AT 00Z WERE T2.5 OR 35 KT FROM BOTH TAFB AND SAB.  ON
THAT BASIS THE SYSTEM IS UPGRADED TO TROPICAL STORM ALVIN...THE
FIRST OF THE 2007 EASTERN NORTH PACIFIC SEASON.  DESPITE THE
UPGRADE...THE SYSTEM IS NOT EXCEPTIONALLY WELL-ORGANIZED...AND
CONDITIONS ALONG THE FORECAST TRACK STILL DO NOT APPEAR TO FAVOR
SIGNIFICANT STRENGTHENING.  THE OFFICIAL INTENSITY FORECAST AGAIN
CALLS FOR ALVIN TO REACH 45 KT DURING THE MIDDLE OF THE FORECAST
PERIOD...OVER SSTS NEAR 28C AND CONTINUING MODERATE EASTERLY WIND
SHEAR...BUT IN A LESS THAN IDEAL THERMODYNAMIC ENVIRONMENT.  THIS
FORECAST IS ABOUT IN THE MIDDLE OF THE VARIOUS INTENSITY GUIDANCE
SOLUTIONS.

I CANNOT ACTUALLY SEE THE LOW-LEVEL CENTER...BUT HAVE ATTEMPTED TO
TRIANGULATE ITS LOCATION USING LOW CLOUD MOTIONS OUTSIDE OF THE
DEEP CONVECTION...AND USING CONTINUITY FROM AN EARLIER TRMM
OVERPASS AT 1859Z.  BEST ESTIMATE OF THE INITIAL MOTION IS
WEST-SOUTHWESTWARD OR 245/5.  THE MAIN STEERING MECHANISM DURING
THE NEXT FEW DAYS WILL BE A MID-LEVEL RIDGE CURRENTLY SITUATED TO
THE NORTHWEST OF ALVIN.  AS THIS RIDGE MIGRATES NORTHEASTWARD
TOWARD MEXICO... ALVIN WILL PROBABLY TURN SLIGHTLY TO THE RIGHT AND
HEAD ALMOST DUE WESTWARD BUT SLOW DOWN LATE IN THE FORECAST PERIOD. 
THE OFFICIAL FORECAST IS JUST A LITTLE SOUTH OF THE PREVIOUS
ADVISORY AND IS SIMILAR TO THE ECMWF GUIDANCE.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/0300Z 12.6N 113.7W    35 KT
 12HR VT     29/1200Z 12.4N 114.4W    35 KT
 24HR VT     30/0000Z 12.3N 115.4W    40 KT
 36HR VT     30/1200Z 12.2N 116.4W    45 KT
 48HR VT     31/0000Z 12.1N 117.5W    45 KT
 72HR VT     01/0000Z 12.0N 119.0W    45 KT
 96HR VT     02/0000Z 12.0N 120.2W    40 KT
120HR VT     03/0000Z 12.0N 121.5W    40 KT
 
$$
FORECASTER KNABB
 
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