000 WTPZ42 KNHC 271432 TCDEP2 TROPICAL STORM BORIS DISCUSSION NUMBER 2 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP022008 800 AM PDT FRI JUN 27 2008 A CONVECTIVE BAND WITH CLOUD TOP TEMPERATURES TO -80C HAS DEVELOPED AROUND THE CENTER OF TROPICAL DEPRESSION TWO-E DURING THE PAST SEVERAL HOURS. SATELLITE INTENSITY ESTIMATES ARE 35 KT FROM BOTH SAB AND TAFB...AND RE-EXAMINATION OF EARLIER SCATTEROMETER DATA SUGGESTED 35 KT WINDS. BASED ON THIS...THE DEPRESSION IS UPGRADED TO TROPICAL STORM BORIS. THE INITIAL INTENSITY IS INCREASED TO 35 KT...AND THIS MAY BE CONSERVATIVE. THE CIRRUS OUTFLOW IS CURRENTLY GOOD IN THE SOUTHWESTERN SEMICIRCLE AND POOR ELSEWHERE. THE INITIAL MOTION IS 295/8. WATER VAPOR IMAGERY AND LARGE-SCALE MODEL ANALYSES SHOW A MID/UPPER-LEVEL TROUGH OVER THE PACIFIC NORTH OF 15N BETWEEN 115-135W. THE MODELS FORECAST THIS TROUGH TO MOVE WESTWARD AND WEAKEN...WITH A MID/UPPER-LEVEL RIDGE BUILDING WESTWARD FROM MEXICO TO THE NORTH OF BORIS. THIS EVOLUTION SHOULD ALLOW BORIS TO MOVE WEST-NORTHWESTWARD FOR 24 HR OR SO...FOLLOWED BY A TURN TOWARD THE WEST AS SHOWN BY THE GFS GFDL AND HWRF. THE FORECAST TRACK FOLLOWS THIS SCENARIO...WITH THE NEW FORECAST BEING A LITTLE NORTH OF AND SLOWER THAN THE PREVIOUS FORECAST. IT IS DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE IN BEST AGREEMENT WITH THE CORRECTED MODEL CONSENSUS. THE ECMWF SHOWS AN ALTERNATE SCENARIO...WITH BORIS BECOMING STATIONARY OR MOVING EASTWARD AFTER 96 HR DUE TO THE DEVELOPMENT OF ANOTHER TROPICAL CYCLONE TO THE EAST. WHILE ANOTHER CYCLONE IS A DISTINCT POSSIBILITY...THE ECMWF MAY BE MAKING THE SYSTEM TOO POWERFUL AND TOO LARGE. THUS...ITS FORECAST TRACK FOR BORIS APPEARS UNLIKELY AT THIS TIME. BORIS IS CURRENTLY IN AN ENVIRONMENT OF LIGHT TO MODERATE EAST-NORTHEASTERLY VERTICAL WIND SHEAR. THE LARGE-SCALE MODELS FORECAST THIS PATTERN TO PERSIST FOR 24-36 HR. AFTER THAT...THEY FORECAST A PIECE OF AN UPPER-LEVEL TROUGH CURRENTLY OVER THE GULF OF MEXICO TO MOVE WESTWARD AND PASS NEAR BORIS...ACCOMPANIED BY A SIGNIFICANT INCREASE IN SHEAR. THIS WOULD LIKELY STOP INTENSIFICATION...SO THE INTENSITY FORECAST CALLS FOR BORIS TO REACH A PEAK INTENSITY OF 50 KT IN ABOUT 48 HR. THE SHEAR IS FORECAST TO DECREASE AFTER 72 HR...BUT BY THAT TIME BORIS IS FORECAST TO MOVE OVER COOLER SEA SURFACE TEMPERATURES. AN ALTERNATIVE SCENARIO BASED ON CURRENT CONVECTIVE TRENDS IS THAT BORIS COULD STRENGTHEN FASTER THAN CURRENTLY FORECAST FOR THE FIRST 36 HR AND REACH A HIGHER PEAK INTENSITY. FORECAST POSITIONS AND MAX WINDS INITIAL 27/1500Z 12.6N 109.3W 35 KT 12HR VT 28/0000Z 13.0N 110.4W 40 KT 24HR VT 28/1200Z 13.3N 111.8W 45 KT 36HR VT 29/0000Z 13.4N 113.5W 50 KT 48HR VT 29/1200Z 13.5N 115.2W 50 KT 72HR VT 30/1200Z 13.5N 118.5W 50 KT 96HR VT 01/1200Z 13.5N 122.0W 40 KT 120HR VT 02/1200Z 13.5N 125.0W 35 KT $$ FORECASTER BEVEN