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| #200245 (Received by flhurricane at: 11:08 AM 10.Jul.2008) TCDAT2 HURRICANE BERTHA DISCUSSION NUMBER 30 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008 1100 AM EDT THU JUL 10 2008 SATELLITE IMAGERY INDICATES THAT THE EYE OF BERTHA HAS BECOME SOMEWHAT RAGGED THIS MORNING...AND THE CONVECTIVE TOPS IN THE EYEWALL HAVE WARMED. THIS HAS RESULTED IN THE SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB DECREASING TO 77 KT. THE INITIAL INTENSITY IS REDUCED TO 80 KT...AND THIS COULD BE A LITTLE GENEROUS. ALTHOUGH BERTHA HAS WEAKENED...THE OUTER BANDING HAS INCREASED DURING THE NIGHT AND NOW SURROUNDS THE EYE AND CENTRAL DENSE OVERCAST. THE CIRRUS OUTFLOW IS FAIR TO GOOD IN ALL DIRECTIONS EXCEPT THE SOUTHEAST...WHERE IT IS POOR TO NON-EXISTENT. THE INITIAL MOTION REMAINS 315/8. BERTHA IS ON THE SOUTH SIDE OF A MID-LEVEL ANTICYCLONE SEEN IN WATER VAPOR IMAGERY NEAR 37N59W. THE ANTICYCLONE WILL WEAKEN AS A MID/UPPER-LEVEL SHORTWAVE TROUGH OVER THE NORTHEASTERN UNITED STATES MOVES INTO THE ATLANTIC DURING THE NEXT 24-36 HOURS. THIS PATTERN EVOLUTION SHOULD CAUSE BERTHA TO TURN NORTHWARD. THE SHORTWAVE TROUGH IS FORECAST TO PASS NORTH OF BERTHA...AND FROM 36-72 HR THE LARGE-SCALE MODELS FORECAST A MID-LEVEL RIDGE TO BUILD NORTH OF THE HURRICANE IN THE WAKE OF THE TROUGH. THE TRACK MODELS RESPOND TO THIS BY FORECASTING ERRATIC MOTION AS BERTHA APPROACHES BERMUDA. THE NEW FORECAST TRACK WILL CALL FOR A SLOW NORTHWARD MOTION DURING THIS TIME AS A COMPROMISE BETWEEN THE VARIOUS TWISTS AND TURNS OF THE TRACK GUIDANCE. HOWEVER...THERE IS A POSSIBILITY THAT BERTHA COULD JOG LEFT OF THE FORECAST TRACK CLOSER TO BERMUDA AS SHOWN BY THE GFS...UKMET...AND CANADIAN MODELS. AFTER 72 HR...A SECOND MID/UPPER-LEVEL TROUGH MOVING INTO THE WESTERN ATLANTIC SHOULD WEAKEN THE RIDGE...WHICH SHOULD CAUSE BERTHA TO MOVE SOMEWHAT FASTER TOWARD THE NORTH. THE INTENSITY FORECAST IS A CONUNDRUM. THE LARGE-SCALE MODELS FORECAST A LARGE UPPER-LEVEL ANTICYCLONE TO DEVELOP OVER BERTHA DURING THE NEXT 24-48 HR WHILE THE SYSTEM IS STILL OVER WARM WATER. THIS ENVIRONMENT SHOULD BE FAVORABLE FOR STRENGTHENING...YET NONE OF THE INTENSITY FORECAST GUIDANCE CALLS FOR SIGNIFICANT STRENGTHENING DURING THIS TIME. GIVEN THE ENVIRONMENT...THE INTENSITY FORECAST WILL BUCK THE MODEL GUIDANCE AND CALL FOR SLIGHT STRENGTHENING DURING THE FIRST 24-36 HR. THEREAFTER...THE LARGE-SCALE MODELS SUGGEST THE POSSIBILITY OF INCREASED VERTICAL WIND SHEAR...ALTHOUGH THEY DIFFER ON THE DETAILS. THIS...COMBINED WITH COOLING SEA SURFACE TEMPERATURES...ARE EXPECTED TO CAUSE BERTA TO SLOWLY WEAKEN. FORECAST POSITIONS AND MAX WINDS INITIAL 10/1500Z 26.5N 60.2W 80 KT 12HR VT 11/0000Z 27.5N 61.0W 80 KT 24HR VT 11/1200Z 28.5N 61.6W 85 KT 36HR VT 12/0000Z 29.5N 62.0W 85 KT 48HR VT 12/1200Z 30.1N 62.0W 80 KT 72HR VT 13/1200Z 31.5N 62.0W 75 KT 96HR VT 14/1200Z 33.5N 61.5W 65 KT 120HR VT 15/1200Z 37.0N 61.0W 55 KT $$ FORECASTER BEVEN |
