ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM ISAAC DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092006 1100 AM EDT THU SEP 28 2006 ALTHOUGH THE CURRENT SATELLITE APPEARANCE IS A LITTLE SKELETAL... A QUIKSCAT PASS NEAR 0845 UTC PROVIDES STRONG EVIDENCE OF AT LEAST 35 KT WINDS IN THE SYSTEM. THUS THE NINTH TROPICAL STORM OF THE YEAR... ISAAC... IS BORN. THE STORM IS ALSO EXHIBITING SOME SUBTROPICAL CHARACTERISTICS WITH A RADIUS OF MAXIMUM WINDS LARGER THAN AVERAGE NEAR 75 NM... AND ALSO AN UPPER LOW IS NEARLY ON TOP OF THE CYCLONE. FURTHER INTENSIFICATION IS POSSIBLE FOR THE NEXT COUPLE OF DAYS AS VERTICAL WIND SHEAR REMAINS RELATIVELY LIGHT WITH UPPER RIDGING NEAR THE STORM. ALTHOUGH SSTS ARE HOVERING NEAR 26C IN THE PATH OF ISAAC... COLDER-THAN-AVERAGE UPPER-LEVEL TEMPERATURES ARE ALSO FORECAST... WHICH WOULD ALLOW FOR MORE INSTABILITY AND MORE CONVECTION. THE INTENSITY FORECAST IS A LITTLE HIGHER THAN SHIPS AND NOT TOO DISSIMILAR FROM THE FSU SUPERENSEMBLE. THE INITIAL MOTION IS 320/7... A LITTLE TO THE RIGHT AND SLOWER THAN EARLIER. A GENERAL NORTHWESTWARD MOTION SHOULD CONTINUE FOR THE NEXT 36 HOURS OR SO AS THE STORM IS STEERED BY MIDDLE-LEVEL RIDGING OVER THE CENTRAL ATLANTIC. THE RIDGE SHOULD STRENGTHEN SOMEWHAT AS WELL DURING THIS TIME AND COULD PUSH THE SYSTEM A LITTLE MORE TO THE LEFT THAN THE CURRENT MOTION. THEREAFTER... AN ENORMOUS TROUGH CURRENTLY OVER THE EASTERN UNITED STATES SHOULD MOVE INTO THE WESTERN ATLANTIC AND STEER THE STORM AWAY FROM BERMUDA AND NORTH AMERICA. HOWEVER... MODEL GUIDANCE IS GENERALLY SUGGESTING THAT THE UPPER RIDGING WILL HOLD A LITTLE LONGER THAN PREVIOUSLY EXPECTED... AND THE TRACK HAS BEEN SHIFTED WESTWARD IN AGREEMENT WITH NHC GUIDANCE. THE OFFICIAL FORECAST IS ON THE EASTERN SIDE OF THE MODEL ENVELOPE... BETWEEN THE UKMET AND THE FSU SUPERENSEMBLE. ISAAC SHOULD BECOME EXTRATROPICAL IN 3-4 DAYS DUE TO IT PASSING NORTH OF THE GULF STREAM AND INCREASING VERTICAL WIND SHEAR. FORECAST POSITIONS AND MAX WINDS INITIAL 28/1500Z 28.2N 54.7W 35 KT 12HR VT 29/0000Z 28.9N 55.4W 40 KT 24HR VT 29/1200Z 29.9N 56.6W 45 KT 36HR VT 30/0000Z 30.9N 57.8W 50 KT 48HR VT 30/1200Z 32.2N 58.8W 50 KT 72HR VT 01/1200Z 35.5N 59.5W 50 KT 96HR VT 02/1200Z 41.5N 56.0W 50 KT...EXTRATROPICAL 120HR VT 03/1200Z 47.5N 46.5W 50 KT...EXTRATROPICAL $$ FORECASTER BLAKE/STEWART NNNN
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Page last modified: Thursday, 28-Sep-2006 14:40:01 UTC