000 WTNT42 KNHC 110255 TCDAT2 SUBTROPICAL STORM OLGA DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL172007 1100 PM EDT MON DEC 10 2007 SATELLITE IMAGERY AND RADAR DATA FROM THE SAN JUAN WSR-88D INDICATE THAT THE LOW PRESSURE SYSTEM CENTERED NEAR THE VIRGIN ISLANDS AND PUERTO RICO HAS ACQUIRED A WELL-DEFINED...THOUGH BROAD...SURFACE CIRCULATION AND ORGANIZED CONVECTION NOT FAR FROM THE CENTER. DUE TO THE PRESENCE OF AN UPPER-LEVEL LOW JUST SOUTH OF THE VIRGIN ISLANDS...IT IS BEING DESIGNATED A SUBTROPICAL CYCLONE. NOAA BUOY 41043 NORTH OF THE CENTER HAS TWICE REPORTED 1-MIN AVERAGE WINDS OF 33 KT AT AN ELEVATION OF 5 METERS...WHICH SUGGESTS TROPICAL-STORM FORCE WINDS ARE OCCURRING AT THE STANDARD SURFACE ELEVATION OF 10 METERS. BASED ON ALL THIS...THE SYSTEM IS UPGRADED TO SUBTROPICAL STORM OLGA. THE INITIAL INTENSITY OF 35 KT IS IN AGREEMENT WITH SUBTROPICAL INTENSITY ESTIMATES OF 35-40 KT FROM TAFB. THE INITIAL MOTION IS 275/13. OLGA IS ON THE SOUTH SIDE OF A STRONG LOW/MID-LEVEL RIDGE OVER THE WESTERN ATLANTIC...FLORIDA... AND THE EASTERN GULF OF MEXICO. THIS RIDGE SHOULD PERSIST FOR THE NEXT SEVERAL DAYS AND STEER OLGA ON A GENERAL WESTWARD TO WEST- SOUTHWESTWARD TRACK. THE FORECAST TRACK FOLLOWS THIS SCENARIO AND IS DOWN THE MIDDLE OF THE SUITE OF DYNAMICAL MODELS. OLGA CURRENTLY HAS GOOD OUTFLOW OVER THE NORTHWESTERN SEMICIRCLE... WITH OUTFLOW AND CONVECTION IN THE SOUTHEASTERN SEMICIRCLE SUPPRESSED BY THE UPPER-LEVEL LOW. IN THE SHORT-TERM...THIS PATTERN IS FAVORABLE FOR SOME STRENGTHENING...AND THE INTENSITY FORECAST CALLS FOR MODEST INTENSIFICATION BEFORE THE CENTER REACHES THE DOMINICAN REPUBLIC ON TUESDAY. AFTER THAT...THE LARGE-SCALE MODELS FORECAST STRONG WESTERLY VERTICAL WIND SHEAR TO DEVELOP ALONG THE FORECAST TRACK. THAT...COMBINED WITH THE LIKELY DISRUPTION OF THE CIRCULATION BY PASSAGE OVER HISPANIOLA...SHOULD CAUSE WEAKENING. THE LARGE-SCALE MODELS FORECAST OLGA TO WEAKEN TO AN INVERTED TROUGH BY 36-48 HR... WHILE THE SHIPS MODEL FORECASTS DISSIPATION IN 60 HR. BASED ON THIS...THE INTENSITY FORECAST CALLS FOR OLGA TO SURVIVE FOR 48 HR BEFORE DISSIPATING. AFTER COORDINATION WITH THE WFO SAN JUAN...IT WAS DECIDED THAT WATCHES AND WARNINGS WERE NOT NEEDED FOR PUERTO RICO SINCE THE TROPICAL STORM-FORCE WINDS ARE CURRENTLY OVER WATER WELL TO THE NORTH AND WEST OF THE CENTER. FORECAST POSITIONS AND MAX WINDS INITIAL 11/0300Z 18.5N 65.3W 35 KT 12HR VT 11/1200Z 18.5N 67.6W 40 KT 24HR VT 12/0000Z 18.4N 70.6W 30 KT...INLAND 36HR VT 12/1200Z 18.0N 73.8W 25 KT...OVER WATER 48HR VT 13/0000Z 17.8N 76.9W 25 KT...DISSIPATING 72HR VT 14/0000Z...DISSIPATED $$ FORECASTER BEVEN