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| #531447 (Received by flhurricane at: 4:53 AM 03.Aug.2012) TCDAT5 TROPICAL STORM ERNESTO DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052012 500 AM AST FRI AUG 03 2012 ERNESTO HAS NOT BECOME ANY BETTER ORGANIZED OVER THE PAST FEW HOURS. APART FROM A COUPLE OF BRIEF CONVECTIVE BURSTS...CLOUD TOPS HAVE WARMED AND SHRUNK AROUND THE CENTER OVERNIGHT. IN ADDITION...DATA FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT SUGGEST THAT WINDS ARE NOT MIXING DOWN TO THE SURFACE VERY EFFECTIVELY...WHICH IS CONSISTENT WITH THE LACKLUSTER CONVECTIVE STRUCTURE. THE INITIAL INTENSITY IS LOWERED TO 40 KT...AND THAT COULD BE SOMEWHAT GENEROUS GIVEN THAT THE HIGHEST 850-MB WINDS FROM THE AIRCRAFT WERE AROUND 45 KT. THE RAPID WESTWARD MOTION OF THE LOW-LEVEL CENTER IS RESULTING IN DEEP-LAYER SHEAR OF AROUND 20 KT AS ANALYZED BY UW-CIMSS AND THE SHIPS MODEL. GIVEN THIS...AND THE SOMEWHAT DRY AIR SEEN IN UPSTREAM SOUNDINGS OVER THE LESSER ANTILLES...ONLY MODEST INTENSIFICATION IS EXPECTED IN THE NEXT DAY OR SO. BEYOND THAT TIME...CONDITIONS APPEAR TO BECOME MORE FAVORABLE FOR INTENSIFICATION AS THE SHEAR DECREASES WHILE ERNESTO MOVES OVER WARMER WATERS. HOWEVER...GIVEN THE CURRENT STRUCTURAL CHALLENGES OF THE CYCLONE AND THE POTENTIAL FOR LAND INTERACTION...THE OFFICIAL FORECAST WILL REMAIN CONSERVATIVE. THE NEW NHC FORECAST IS SIMILAR TO THE PREVIOUS ONE...AND IS BETWEEN THE MORE AGGRESSIVE SHIPS AND LGEM MODELS AND THE IV15 CONSENSUS THAT INCLUDES THE HFIP GUIDANCE. THE INITIAL MOTION ESTIMATE IS 275/21...AS ERNESTO IS BEING STEERED RAPIDLY WESTWARD BY THE STRONG SUBTROPICAL RIDGE TO ITS NORTH. THIS RIDGE IS FORECAST BY THE GLOBAL MODELS TO BUILD WESTWARD FOR THE NEXT 2 TO 3 DAYS...WHICH SHOULD RESULT IN A CONTINUED WESTWARD MOTION OF THE CYCLONE. AFTER 72 HOURS...THE MODELS SHOW A WEAKNESS DEVELOPING IN THE RIDGE AS A MID-LATITUDE TROUGH MOVES INTO THE EASTERN UNITED STATES. THIS SHOULD LEAD TO A SLOWER WEST-NORTHWARD MOTION BY THE END OF THE PERIOD. THERE CONTINUES TO BE CONSIDERABLE SPREAD IN THE GUIDANCE AT DAYS 3 THROUGH 5...WITH THE ECMWF SHOWING A WEAKER SYSTEM MOVING WESTWARD AND THE STRONGER GFDL TURNING ERNESTO MORE TOWARD THE NORTHWEST. DUE TO THE INITIAL MOTION...THE NEW NHC FORECAST IS A LITTLE FASTER THAN THE PREVIOUS ADVISORY THROUGH 48 HOURS. AFTER THAT TIME...THE NHC FORECAST IS LARGELY AN UPDATE OF THE PREVIOUS ONE AND IS CLOSE TO THE MIDDLE OF THE GUIDANCE ENVELOPE AND THE TVCA/TV15 MULTI-MODEL CONSENSUS. GIVEN THE LARGE MODEL SPREAD AND THE DEPENDENCE OF THE TRACK ON THE FUTURE INTENSITY OF THE CYCLONE...CONFIDENCE IN THE TRACK FORECAST LATE IN THE PERIOD IS LOWER THAN USUAL. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 13.5N 60.7W 40 KT 45 MPH 12H 03/1800Z 14.0N 63.5W 45 KT 50 MPH 24H 04/0600Z 14.4N 66.7W 50 KT 60 MPH 36H 04/1800Z 14.9N 69.7W 55 KT 65 MPH 48H 05/0600Z 15.6N 72.8W 60 KT 70 MPH 72H 06/0600Z 17.0N 78.5W 65 KT 75 MPH 96H 07/0600Z 18.5N 82.5W 70 KT 80 MPH 120H 08/0600Z 20.5N 86.0W 75 KT 85 MPH $$ FORECASTER BRENNAN |
