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| #200300 (Received by flhurricane at: 4:52 PM 10.Jul.2008) TCDAT2 HURRICANE BERTHA DISCUSSION NUMBER 31 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008 500 PM EDT THU JUL 10 2008 A RECENT TRMM OVERPASS AND GOES VISIBLE IMAGERY INDICATE THAT THE OUTER CONVECTIVE BANDING NOTED EARLIER HAS WRAPPED UP INTO AN OUTER EYEWALL WITH A DIAMETER OF ABOUT 75 N MI. THIS FEATURE SURROUNDS THE ORIGINAL INNER EYE WHICH IS ABOUT 10 N MI WIDE. BASED ON SATELLITE INTENSITY ESTIMATES AND WARMING OF THE CLOUD TOPS IN THE INNER EYEWALL...THE INITIAL INTENSITY IS REDUCED TO 75 KT. THE CIRRUS OUTFLOW REMAINS GOOD IN THE NORTHWESTERN SEMICIRCLE...AND HAS INCREASED SINCE THIS MORNING IN THE SOUTHEASTERN SEMICIRCLE. THE INITIAL MOTION IS 315/9. WATER VAPOR IMAGERY SHOWS A COMPLEX STEERING PATTERN...CONSISTING OF A BROAD MID/UPPER-LEVEL TROUGH OVER THE NORTHEASTERN UNITED STATES AND A MID-LEVEL RIDGE NORTH OF BERTHA THAT ARE MOVING EASTWARD...AND AN UPPER-LEVEL LOW NEAR 28N69W THAT IS MOVING SLOWLY WESTWARD. IN THE SHORT TERM...THIS PATTERN SHOULD CAUSE BERTHA TO TURN NORTHWARD AS SHOWN IN THE NEW FORECAST TRACK. DURING THE 36-72 HR PERIOD...A MID-LEVEL RIDGE DEVELOPING BEHIND THE SHORTWAVE TROUGH IS LIKELY TO BLOCK BERTHA'S NORTHWARD MOTION...WITH THE POSSIBILITY OF ERRATIC MOTION NEAR OR TO THE EAST OF BERMUDA. THEREAFTER...THE LARGE-SCALE MODELS CURRENTLY AGREE THAT A SECOND TROUGH MOVING THROUGH THE NORTHWESTERN ATLANTIC WILL BYPASS BERTHA...LEAVING THE STORM TRAPPED IN THE SUBTROPICAL RIDGE TO THE NORTH OR NORTHEAST OF BERMUDA. IN A MAJOR SHIFT FROM PREVIOUS RUNS...NONE OF THE DYNAMICAL MODELS SHOW BERTHA REACHING 40N IN 5 DAYS. BASED ON THIS...THE FORECAST TRACK WILL CALL FOR A SLOWER NORTHWARD MOTION THAN IN THE PREVIOUS PACKAGE... WITH THE TRACK SMOOTHING THROUGH SOME OF THE ERRATIC MOTION FORECASTS IN THE MODELS. THE NEW TRACK IS CLOSER TO BERMUDA THAN THE PREVIOUS TRACK...AND BERTHA COULD COME EVEN CLOSER TO BERMUDA IF THE JOGS TO THE LEFT IN THE UKMET AND CANADIAN MODELS VERIFY. AN UPPER-LEVEL ANTICYCLONE IS BUILDING OVER BERTHA...AND THE STORM STILL HAS A DAY OR TWO MORE OVER WARM SEA SURFACE TEMPERATURES. THUS...EVEN THOUGH NONE OF THE FORECAST MODELS CALL FOR SIGNIFICANT STRENGTHENING...THE HURRICANE COULD RE-INTENSIFY AT THE END OF THE EYEWALL REPLACEMENT CYCLE. BASED ON THIS...THE NEW INTENSITY FORECAST CALLS FOR MODEST STRENGTHENING IN 24 HR. LATER IN THE FORECAST PERIOD...BERTHA IS EXPECTED TO MOVE OUT FROM UNDER THE ANTICYCLONE AND ENCOUNTER VERTICAL WIND SHEAR. THIS SHOULD OCCUR AS BERTHA REACHES COOLER WATERS AND RESULT IN A WEAKENING TREND. FORECAST POSITIONS AND MAX WINDS INITIAL 10/2100Z 27.2N 60.8W 75 KT 12HR VT 11/0600Z 28.0N 61.7W 75 KT 24HR VT 11/1800Z 29.0N 62.2W 80 KT 36HR VT 12/0600Z 29.8N 62.5W 80 KT 48HR VT 12/1800Z 30.5N 62.5W 75 KT 72HR VT 13/1800Z 31.5N 62.5W 70 KT 96HR VT 14/1800Z 33.0N 62.5W 60 KT 120HR VT 15/1800Z 36.0N 62.0W 50 KT $$ FORECASTER BEVEN |
