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| #199167 (Received by flhurricane at: 5:08 AM 05.Jul.2008) TCDAT2 TROPICAL STORM BERTHA DISCUSSION NUMBER 9 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008 500 AM EDT SAT JUL 05 2008 BERTHA IS PASSING OVER SEA-SURFACE TEMPERATURES OF ROUGHLY 25 DEGREES CELSIUS...ABOUT THE COOLEST THE CYCLONE HAS ENCOUNTERED YET DURING THE USUAL DIURNAL CONVECTIVE MAXIMUM...AND IT HAS BEEN STRUGGLING TO PRODUCE VERY MUCH DEEP CONVECTION OVERNIGHT. DVORAK INTENSITY ESTIMATES AT 06Z WERE 35-45 KT...AND WHILE IT IS POSSIBLE THE WINDS HAVE WEAKENED...THE ADVISORY INTENSITY WILL REMAIN 45 KT FOR NOW. DURING THE NEXT THREE DAYS...BERTHA HAS AN OPPORTUNITY TO STRENGTHEN AS THE UNDERLYING WATER TEMPERATURES STEADILY WARM BY ABOUT A DEGREE CELSIUS PER DAY ALONG THE FORECAST TRACK. ALL OF THE OBJECTIVE INTENSITY MODELS FORECAST INTENSIFICATION THROUGH 72 HOURS...WITH THE SHIPS AND LGEM REACHING 65 KT BY THEN...WHILE HWRF AND GFDL ARE MORE CONSERVATIVE. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF THESE SOLUTIONS AND IS THE SAME AS THE PREVIOUS ADVISORY IN PEAKING AT 60 KT. ONE SHOULD NOT PAY TOO MUCH ATTENTION TO THE EXACT INTENSITY FORECAST...HOWEVER. THE MAXIMUM WIND SPEED PROBABILITY TABLE INCLUDED IN THIS FORECAST PACKAGE INDICATES ROUGHLY EQUAL CHANCES OF BERTHA BEING A TROPICAL STORM OR A HURRICANE AT 3 TO 5 DAYS. WHETHER OR NOT BERTHA BECOMES A HURRICANE WOULD SEEM TO DEPEND ON HOW WELL IT SURVIVES ITS STAY OVER COOLER WATERS...AND JUST HOW MUCH WIND SHEAR IMPACTS THE CYCLONE ONCE IT REACHES THE WARMER WATERS...AND BOTH OF THOSE FACTORS ARE SOMEWHAT UNCERTAIN RIGHT NOW. A COUPLE OF RECENT MICROWAVE OVERPASSES FROM AMSU AND AMSR-E PROVIDE THE BASIS FOR THE INITIAL MOTION ESTIMATE OF 285/18. OVERALL THE DYNAMICAL MODEL GUIDANCE PROVIDES NO STRONG INDICATION THAT BERTHA WILL DEVIATE MUCH FROM THE CURRENT WEST-NORTHWESTWARD HEADING DURING THE NEXT SEVERAL DAYS. THE WEAKNESS IN THE SUBTROPICAL RIDGE CURRENTLY ALONG ABOUT 55W IS FORECAST BY THE MODELS TO BECOME LESS PRONOUNCED AND TO PROPAGATE EASTWARD DURING THE NEXT COUPLE OF DAYS...AND MOST OF THE GUIDANCE TRACKS SHOW BERTHA BYPASSING THIS FEATURE WITH JUST A SLIGHT BEND TO THE RIGHT ON DAYS 3 THROUGH 5. THE HWRF IS THE ONLY DYNAMICAL MODEL CURRENTLY CALLING FOR BERTHA TO TURN NORTHWARD BEFORE REACHING 60W. THE MODEL CONSENSUS HAS HARDLY BUDGED ON THIS CYCLE...AND THE NEW OFFICIAL TRACK FORECAST IS ADJUSTED ONLY SLIGHTLY FASTER AND TO THE LEFT AT DAYS 3 THROUGH 5. THIS NEW TRACK IS MOST SIMILAR TO THE GFDL...GFS...AND ECMWF...BUT THE TRACK FORECAST UNCERTAINTY REMAINS SIGNIFICANT AS REFLECTED BY THE CONTINUING LARGE SPREAD IN THE LONG-RANGE MODEL GUIDANCE. FORECAST POSITIONS AND MAX WINDS INITIAL 05/0900Z 16.5N 35.3W 45 KT 12HR VT 05/1800Z 17.0N 38.0W 45 KT 24HR VT 06/0600Z 17.6N 41.8W 50 KT 36HR VT 06/1800Z 18.2N 45.6W 55 KT 48HR VT 07/0600Z 19.0N 49.3W 60 KT 72HR VT 08/0600Z 20.5N 56.0W 60 KT 96HR VT 09/0600Z 22.5N 61.0W 60 KT 120HR VT 10/0600Z 24.5N 66.0W 60 KT $$ FORECASTER KNABB |
