000 WTPZ41 KNHC 290259 TCDEP1 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