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| #198911 (Received by flhurricane at: 10:37 PM 03.Jul.2008) TCDAT2 TROPICAL STORM BERTHA DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008 1100 PM EDT THU JUL 03 2008 BERTHA'S SATELLITE PRESENTATION HAS IMPROVED DURING THE LAST 6 HOURS COURTESY OF A NEW BURST OF DEEP CONVECTION THAT BEGAN AROUND 1900 UTC. BANDING FEATURES ARE ALSO BECOMING MORE PROMINENT IN BOTH CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY. BASED ON THIS TREND...THE INITIAL INTENSITY IS RAISED TO 40 KT WHICH IS A COMPROMISE BETWEEN DVORAK INTENSITY ESTIMATES OF 45 KT AND 35 KT FROM TAFB AND SAB...RESPECTIVELY. DURING THE NEXT COUPLE OF DAYS...BERTHA IS FORECAST TO BE LOCATED WITHIN A FAVORABLE ATMOSPHERIC ENVIRONMENT BUT OVER MARGINALLY WARM SSTS. SUCH CONDITIONS SHOULD ALLOW FOR SLOW STRENGTHENING IN THE SHORT-TERM. THE OFFICIAL INTENSITY FORECAST IS ESSENTIALLY AN UPDATE OF THE PREVIOUS ONE AND KEEPS BERTHA JUST BELOW HURRICANE STRENGTH OUT OF RESPECT OF THE HWRF MODEL. BEYOND 72 HOURS...VERTICAL SHEAR IS FORECAST TO INCREASE AND THIS IS REFLECTED IN THE OFFICIAL FORECAST WITH ARRESTED DEVELOPMENT. A SERIES OF VERY USEFUL MICROWAVE PASSES INDICATES THAT BERTHA IS A LITTLE FARTHER SOUTH THAN PREVIOUSLY THOUGHT WITH AN INITIAL MOTION MORE TOWARDS THE WEST...280/12. IT WOULD APPEAR THAT THE RECENT BURST OF CONVECTION IS CAUSING THE CYCLONE TO RESPOND TO THE LARGE MIDDLE TO UPPER-LEVEL RIDGE TO ITS NORTH. THIS RIDGE SHOULD KEEP BERTHA ON A GENERAL WEST-NORTHWESTWARD HEADING OVER THE NEXT 2-3 DAYS. THEREAFTER...MOST OF THE DYNAMICAL MODELS INDICATE A TURN TOWARDS THE NORTHWEST AS BERTHA REACHES A BREAK IN THE RIDGE. EVEN THOUGH BOTH THE UKMET AND ECMWF SHOW A SIMILAR EVOLUTION IN THE LARGE-SCALE PATTERN...THESE MODELS KEEP A WEAKER AND SHALLOWER CYCLONE ON A WEST-NORTHWESTWARD MOTION THROUGH THE ENTIRE FORECAST. SINCE THE OFFICIAL FORECAST ASSUMES BERTHA WILL REMAIN A DEEP SYSTEM...A TURN TOWARDS THE NORTHWEST IS INDICATED BEYOND 72 HOURS. THIS IS SIMILAR TO THE PREVIOUS FORECAST...ALBEIT A BIT FARTHER SOUTH TO ACCOUNT FOR THE INITIAL POSITION RELOCATION. FORECAST POSITIONS AND MAX WINDS INITIAL 04/0300Z 13.4N 27.0W 40 KT 12HR VT 04/1200Z 13.8N 29.2W 45 KT 24HR VT 05/0000Z 14.6N 32.5W 45 KT 36HR VT 05/1200Z 15.5N 35.9W 50 KT 48HR VT 06/0000Z 16.6N 39.4W 55 KT 72HR VT 07/0000Z 18.5N 45.5W 60 KT 96HR VT 08/0000Z 21.5N 51.0W 60 KT 120HR VT 09/0000Z 25.5N 54.0W 60 KT $$ FORECASTER RHOME |
