000 WTPZ45 KNHC 142031 TCDEP5 TROPICAL STORM ISELLE DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP102008 200 PM PDT THU AUG 14 2008 TROPICAL STORM ISELLE HAS WEAKENED AS NORTHEASTERLY VERTICAL WIND SHEAR HAS INCREASED ACROSS THE CYCLONE. THE ADVISORY INTENSITY IS BASED ON A CONSENSUS SATELLITE INTENSITY ESTIMATE OF 40 KT FROM TAFB AND SAB. TROPICAL STORM ISELLE HAS MADE A SLIGHT JOG TO THE WEST DURING THE PAST 6 HOURS...BUT THIS MAY BE A TEMPORARY MOTION DUE TO THE EARLIER WEAKENING OF THE INNER-CORE CONVECTION. HOWEVER... CONVECTION IN THE SOUTHWESTERN QUADRANT HAS REDEVELOPED...SO A TURN TO THE WEST-NORTHWEST IS EXPECTED TO RESUME AND CONTINUE FOR THE NEXT 48 HOURS OR SO. AFTERWARD...A SHALLOW TROPICAL DEPRESSION OR REMNANT LOW IS FORECAST TO TURN WESTWARD AS THE CIRCULATION GETS STEERED BY THE LOW-LEVEL EASTERLIES NORTH OF THE SYSTEM...AND ALSO POSSIBLY DUE TO INTERACTION WITH A LARGER CYCLONIC GYRE SITUATED TO THE WEST-SOUTHWEST OF ISELLE. ALL OF THE NHC MODEL GUIDANCE NOW SUPPORTS THIS SCENARIO AND THERE ARE NO LONGER ANY MODELS THAT TAKE ISELLE TOWARD SOUTHERN BAJA CALIFORNIA. THE OFFICIAL FORECAST TRACK IS SOUTH OF THE PREVIOUS TRACK AND IS SIMILAR TO THE NHC MODEL CONSENSUS. HOSTILE VERTICAL WIND SHEAR CONDITIONS OF 25 TO 30 KT THROUGH 96 HOURS ARE FORECAST TO PERSIST...AND THESE UNFAVORABLE UPPER-LEVEL CONDITIONS...COMBINED WITH STEADILY DECREASING SEA-SURFACE TEMPERATURES...ARE EXPECTED TO CAUSE GRADUAL WEAKENING OF THE CYCLONE THROUGHOUT THE FORECAST CYCLE WITH ISELLE POSSIBLY BECOMING A NON-CONVECTIVE LOW PRESSURE SYSTEM BY 72-96 HOURS. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE SHIPS INTENSITY MODEL. FORECAST POSITIONS AND MAX WINDS INITIAL 14/2100Z 17.8N 110.2W 40 KT 12HR VT 15/0600Z 18.3N 111.2W 40 KT 24HR VT 15/1800Z 18.9N 112.4W 35 KT 36HR VT 16/0600Z 19.5N 113.5W 35 KT 48HR VT 16/1800Z 19.8N 114.5W 30 KT 72HR VT 17/1800Z 20.0N 116.0W 30 KT 96HR VT 18/1800Z 20.0N 117.5W 25 KT 120HR VT 19/1800Z 20.0N 119.0W 20 KT $$ FORECASTER STEWART/PASCH