ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM TROPICAL STORM HELENE DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 1100 PM AST WED SEP 13 2006 INFRARED SATELLITE IMAGERY THIS EVENING INDICATES CONTINUED GRADUAL DEVELOPMENT WITH A DISTINCT CURVED BAND ON THE NORTHWESTERN SEMI-CIRCLE. BASED UPON UNANIMOUS DVORAK T-NUMBERS OF 2.5 AND EARLIER AMSU INTENSITY ESTIMATES...THE INTENSITY IS ANALYZED AT 35 KT AND IS GIVEN THE NAME HELENE. THE TROPICAL STORM APPEARS TO HAVE SPED UP WITH AN INITIAL MOTION OF 285/19...THOUGH THIS IS SOMEWHAT UNCERTAIN GIVEN THE SPREAD IN POSITIONS. HELENE SHOULD CONTINUE WEST-NORTHWESTWARD FOR THE NEXT DAY UNDER THE INFLUENCE OF A DEEP-LAYER RIDGE. BETWEEN 36 AND 72 HOURS...A MID TO UPPER TROUGH INDUCES A WEAKNESS IN THE RIDGE AND THIS MAY ACT TO STEER THE SYSTEM TOWARD THE NORTHWEST. AFTER THIS TROUGH BY-PASSES HELENE...A WEST-NORTHWESTWARD TRACK SHOULD RESUME AT DAYS 4 AND 5. ALL RELIABLE GUIDANCE SHOWS THIS STAIR-STEP SCENARIO...WITH NOGAPS BEING A MODEST OUTLIER TO THE SOUTHWEST OF THE PACK. THE FORECAST TRACK IS NEAR THE MODEL CONSENSUS AND IS TO THE RIGHT OF THE PREVIOUS FORECAST. WHILE THERE IS A LARGE SAHARAN AIR LAYER TO THE NORTH AND WEST OF HELENE...TOTAL PRECIPITABLE WATER ANALYSES FROM CIRA SUGGEST THAT THIS VERY DRY AIR IS NOT REACHING HELENE'S INNER CORE. THE SYSTEM'S PROJECTED TRACK SHOULD TAKE IT OVER WARM WATER...THROUGH ABUNDANT MOISTURE AND INTO LIGHT VERTICAL SHEAR FOR THE NEXT THREE DAYS. SHIPS AND THE FSU SUPER-ENSEMBLE THUS BRING HELENE UP TO ABOUT 100 KT IN THREE DAYS. THE GFDL...ON THE OTHER HAND...IS SUBSTANTIALLY WEAKER...LIKELY BECAUSE IT DEPICTS MORE SHEAR BEING IMPARTED ON HELENE DUE TO THE AFOREMENTIONED MID TO UPPER TROUGH. AT DAYS 4 AND 5...ALL GUIDANCE SUGGESTS THE SHEAR WILL PICK UP AND LIMIT FURTHER INTENSIFICATION. THE INTENSITY FORECAST IS CLOSE TO...BUT JUST BELOW...BOTH SHIPS AND THE FSU SUPER-ENSEMBLE. FORECAST POSITIONS AND MAX WINDS INITIAL 14/0300Z 13.3N 32.7W 35 KT 12HR VT 14/1200Z 13.7N 35.0W 45 KT 24HR VT 15/0000Z 14.7N 37.4W 55 KT 36HR VT 15/1200Z 15.9N 39.5W 65 KT 48HR VT 16/0000Z 17.4N 41.0W 75 KT 72HR VT 17/0000Z 20.0N 43.5W 90 KT 96HR VT 18/0000Z 21.5N 45.5W 95 KT 120HR VT 19/0000Z 22.5N 49.0W 85 KT $$ FORECASTER AVILA/LANDSEA NNNN
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Page last modified: Thursday, 14-Sep-2006 03:00:01 UTC