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| #113597 (Received by flhurricane at: 10:40 AM 29.Sep.2006) TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092006 1100 AM EDT FRI SEP 29 2006 SATELLITE IMAGES INDICATE THAT ISAAC IS MAINTAINING ITS SMALL CORE WITH MODERATE CONVECTION IN BANDS AROUND THE CENTER. A QUIKSCAT PASS AT 0958 UTC THIS MORNING SHOWED THAT THE MAXIMUM WINDS OF ISAAC REMAIN AROUND 40 KT. QUIKSCAT ALSO INDICATES THE STORM HAS DECREASED SOMEWHAT IN SIZE AND THE WIND RADII ARE ADJUSTED INWARD. THERE ARE NO CHANGES TO THE INTENSITY FORECAST PHILOSOPHY THIS MORNING. LATER TODAY THE TROPICAL CYCLONE WILL BE MOVING OVER WARMER WATER AND EXPERIENCING ONLY MODEST VERTICAL WIND SHEAR. THESE FACTORS... PLUS INCREASING MOISTURE ALOFT BASED ON THE SHIPS MODEL... SHOULD HELP INITIATE A SLOW INTENSIFICATION TREND. BY 36 TO 48 HOURS... SHEAR IS FORECAST TO INCREASE AND LIMIT STRENGTHENING. THE INTENSITY FORECAST IS BASICALLY THE SAME AS BEFORE. HOWEVER... IT IS WORTH NOTING THAT SHIPS AND GFDL INTENSIFY THE CYCLONE MORE THAN THE OFFICIAL FORECAST AFTER RECURVATURE. THIS SCENARIO SEEMS UNLIKELY GIVEN THE STRONG SHEAR FORECAST AND SHARPLY DECREASING SSTS. ISAAC HAS CONTINUED TO TURN MORE WESTWARD AND IS NOW MOVING 290/5. THE BIGGEST QUESTION IN THE TRACK FORECAST IS HOW LONG DOES THE WEST-NORTHWESTWARD MOTION CONTINUE BEFORE A TURN BACK TOWARD THE NORTHWEST BEGINS. THE ECMWF AND NOGAPS MODELS SUGGEST RIDGING WILL HOLD NORTH OF THE STORM FOR ABOUT 48 HOURS BEFORE STARTING A MORE NORTHWARD MOTION. THE UKMET CONTINUES TO BE ON THE RIGHT-HAND SIDE OF THE GUIDANCE BY SUGGESTING A NORTH-NORTHWEST MOTION IN AS LITTLE AS 24 HOURS. IN GENERAL... GLOBAL MODELS HAVE BEEN TRENDING A LITTLE TO THE LEFT AND THE OFFICIAL FORECAST IS NUDGED IN THAT DIRECTION... A TOUCH TO THE WEST OF THE PREVIOUS FORECAST. THE FORECAST TRACK DURING THE EXTRATROPICAL STAGE REMAINS UNCERTAIN DUE TO SOME SPREAD IN THE TRACK GUIDANCE. THE COMPUTER MODELS THAT TAKE THE STORM FARTHEST TO THE WEST ALSO MAKE ISAAC EXTRATROPICAL SOONER AS IT INTERACTS WITH A DEEP TROUGH IN THE WEST ATLANTIC OCEAN. IN ADDITION THESE WESTWARD MODELS AND THE GFS ALSO ABSORB ISAAC INTO A LARGER MID-LATITUDE LOW IN ABOUT 3 DAYS. FOR NOW ISSAC IS FORECAST TO REMAIN SEPARATE FROM THE OTHER EXTRATROPICAL LOW. HOWEVER IF THE WESTWARD TREND CONTINUES... THEN THE REMNANTS OF ISAAC COULD BECOME INDISTINCT FROM THE MID-LATITUDE LOW BY 96 HOURS. FORECAST POSITIONS AND MAX WINDS INITIAL 29/1500Z 29.4N 56.2W 40 KT 12HR VT 30/0000Z 29.9N 57.1W 45 KT 24HR VT 30/1200Z 30.7N 58.3W 45 KT 36HR VT 01/0000Z 31.9N 59.6W 50 KT 48HR VT 01/1200Z 33.8N 60.5W 50 KT 72HR VT 02/1200Z 41.6N 58.4W 50 KT...EXTRATROPICAL 96HR VT 03/1200Z 47.0N 49.0W 50 KT...EXTRATROPICAL 120HR VT 04/1200Z 49.0N 37.0W 50 KT...EXTRATROPICAL $$ FORECASTER BLAKE/STEWART |
