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| #7655 (Received by flhurricane at: 10:40 PM 08.Sep.2004) TCDAT4 HURRICANE IVAN DISCUSSION NUMBER 27 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT WED SEP 08 2004 IVAN WENT THROUGH A PERIOD OF RAPID DEEPENING THIS AFTERNOON...WITH THE CENTRAL PRESSURE FALLING FROM 951 TO 938 MB IN A PERIOD OF ABOUT 5.5 HOURS. THE MAXIMUM 700 MB FLIGHT LEVEL-WINDS WERE 131 KT...AND A NORTHEAST EYEWALL DROPSONDE SUGGESTED SURFACE WINDS NEAR 120 KT. BASED ON THE DROPSONDE AND THE PRESSURE...THE MAXIMUM INTENSITY IS INCREASED TO 125 KT...WHICH IS IN GOOD AGREEMENT WITH 127 KT SATELLITE INTENSITY ESTIMATES FROM TAFB...SAB...AND AFWA. THE SATELLITE SIGNATURE OF THE HURRICANE HAS NOT CHANGED SIGNIFICANTLY SINCE THE HURRICANE HUNTER LEFT...SO IT IS UNKNOWN IF THE DEEPENING HAS CONTINUED. THE INITIAL INTENSITY COULD BE A LITTLE CONSERVATIVE. IVAN HAS NUDGED A LITTLE TO THE LEFT DURING THE EVENING AND THE INITIAL MOTION IS NOW 290/15. THERE IS LITTLE CHANGE TO THE FORECAST PHILOSOPHY DURING THE FIRST 48 HR...AS IVAN SHOULD CONTINUE WEST-NORTHWESTWARD TOWARD JAMAICA ON THE SOUTH SIDE OF THE SUBTROPICAL RIDGE. THINGS GETS MORE UNCERTAIN AFTER 48 HR...AS THE RIDGE STARTS TO WEAKEN DUE TO A DIGGING MID/UPPER-LEVEL TROUGH OVER THE EASTERN UNITED STATES AND AN UPPER-LEVEL LOW MOVING WESTWARD UNDER THE RIDGE. THIS COMBINATION SHOULD ALLOW IVAN TO TURN NORTHWESTWARD AND EVENTUALLY NORTHWARD...WITH THE USUAL QUESTIONS OF WHERE AND WHEN. THE GFS...GFDL...NOGAPS...AND FSU SUPERENSEMBLE HAVE ALL SHIFTED TO THE RIGHT...WITH THE GFS RECURVING IVAN THROUGH THE BAHAMAS...THE GFDL MOVING IT INTO SOUTHEASTERN FLORIDA...THE NOGAPS MOVING IT UP THE LENGTH OF THE FLORIDA PENINSULA...AND THE SUPERENSEMBLE PASSING JUST WEST OF KEY WEST. GIVEN THE INCONSISTENCY OF THE MODELS...AND THE LEFTWARD NUDGE THAT OCCURRED THIS EVENING...THE FORECAST TRACK WILL NOT SHIFT AS FAR EAST AS THE GUIDANCE AT THIS TIME. THE NEW TRACK IS SHIFTED A LITTLE WEST OF THE PREVIOUS TRACK FOR THE FIRST 24-36 HR AND THEN SOMEWHAT TO THE RIGHT AFTER 72 HR. THE INTENSITY FORECAST CALLS FOR IVAN TO REACH 135 KT IN 12 HR ON THE PREMISE THAT THE AFTERNOON STRENGTHENING WILL CONTINUE. AFTER THAT...VARIOUS ANALYSES INDICATE THAT IVAN SHOULD PASS OVER COOLER SEA SURFACE TEMPERATURES AND REDUCED MAXIMUM POTENTIAL INTENSITY FOR ABOUT 24 HR. THIS COMBINED WITH AN EXPECTED CONCENTRIC EYEWALL CYCLE SHOULD CAUSE SOME WEAKENING. WARMER WATER AWAITS OVER THE NORTHWESTERN CARIBBEAN AND THE STRAITS OF FLORIDA...WHICH WOULD ALLOW SOME STRENGTHENING WHEN IVAN IS NOT HITTING LAND OR UNDERGOING CONCENTRIC EYEWALL CYCLES. AFTER 96 HR...SOME WESTERLY SHEAR MAY DEVELOP AND THE INTENSITY FORECAST REFLECTS A SLIGHT WEAKENING AT 120 HR. WHILE THE INTENSITY UPS AND DOWNS MAY BE MORE PRONOUNCED THAN FORECAST HERE...IVAN IS EXPECTED TO REMAIN A MAJOR HURRICANE THROUGH THE FORECAST PERIOD. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 09/0300Z 13.6N 69.1W 125 KT 12HR VT 09/1200Z 14.5N 71.0W 135 KT 24HR VT 10/0000Z 15.9N 73.4W 130 KT 36HR VT 10/1200Z 17.4N 75.6W 125 KT 48HR VT 11/0000Z 18.6N 77.5W 120 KT...NEAR JAMAICA 72HR VT 12/0000Z 21.0N 80.0W 125 KT 96HR VT 13/0000Z 23.5N 82.0W 120 KT 120HR VT 14/0000Z 27.0N 82.5W 115 KT |
