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| #106109 (Received by flhurricane at: 4:55 PM 25.Aug.2006) TCDAT5 TROPICAL STORM ERNESTO DISCUSSION NUMBER 5 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL052006 500 PM EDT FRI AUG 25 2006 REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER INDICATE THAT TROPICAL DEPRESSION FIVE HAS STRENGTHENED INTO TROPICAL STORM ERNESTO. THE AIRCRAFT FOUND 48 KT WINDS AT A FLIGHT LEVEL OF 1000 FT ABOUT 40 N MI NORTHEAST OF THE CENTER...ALONG WITH A MINIMUM CENTRAL PRESSURE OF 1004 MB. THIS WIND WOULD NORMALLY SUPPORT A 40 KT INTENSITY. HOWEVER...THE CENTER WAS COMPLETELY EXPOSED AT THAT TIME...AND THE 48 KT WINDS WERE NOT IN SIGNIFICANT CONVECTION. THUS...THE INITIAL INTENSITY IS SET TO A MORE CONSERVATIVE 35 KT IN AGREEMENT WITH SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB. THE EXPOSED CENTER IS TO THE NORTH OF THE PREVIOUS TRACK...AND THE NEW INITIAL MOTION IS A SOMEWHAT UNCERTAIN 285/14. OTHERWISE... THERE IS LITTLE CHANGE IN THE FORECAST PHILOSOPHY OR THE TRACK FORECAST FOR THE FIRST 72 HR. ERNESTO IS SOUTH OF A LOW/MID-LEVEL RIDGE OVER THE WESTERN ATLANTIC...WHICH SHOULD KEEP THE SYSTEM MOVING GENERALLY WEST-NORTHWESTWARD. MODEL GUIDANCE SUPPORTS THIS SCENARIO WITH A TIGHT CLUSTERING OF TRACKS THROUGH THE NORTHWESTERN CARIBBEAN AND THE WESTERN END OF CUBA...WITH THE EXCEPTION OF THE GFDL WHICH CONTINUES TO CALL FOR A TRACK OVER THE LENGTH OF CUBA. SOME SPREAD APPEARS IN THE GUIDANCE AFTER 72 HR...WITH THE GFS BUILDING THE RIDGE ACROSS THE GULF OF MEXICO ENOUGH TO TURN ERNESTO WESTWARD...WHILE THE ECMWF AND CANADIAN MODELS HAVING ENOUGH OF A WEAKNESS FOR THE CYCLONE TO TURN NORTHWARD. THE UKMET FORECASTS A CONTINUED WEST-NORTHWESTWARD MOTION THROUGH 120 HR...WHILE THE NOGAPS STALLS ERNESTO OVER THE CENTRAL GULF OF MEXICO. THE NEW FORECAST TRACK IS NORTH OF...BUT PARALLEL TO...THE PREVIOUS TRACK FOR THE FIRST 72 HR BASED ON THE NEW POSITION AND MOTION. IT THEN CALLS FOR A SLOWER NORTHWESTWARD MOTION OVER THE GULF OF MEXICO IN RESPONSE TO THE GUIDANCE SPREAD. SATELLITE IMAGERY STILL SHOWS UPPER-LEVEL SOUTHWESTERLY FLOW JUST NORTHWEST OF ERNESTO. THIS SUGGESTS THAT THE CURRENT SHEAR WILL CONTINUE FOR ANOTHER 12 HR OR SO...WITH TRANSIENT BURSTS OF STRONG CONVECTION LIKELY. AFTER THAT...THE LARGE-SCALE MODELS ALL FORECAST AN UPPER-LEVEL RIDGE OR ANTICYCLONE TO BUILD OVER THE NORTHWESTERN CARIBBEAN. WHILE THERE ARE DIFFERENCES IN THE DETAILS...PARTICULARLY IN THE EXACT POSITION OF THE ANTICYCLONE AND A SOUTHWARD-MOVING CYCLONIC SHEAR AXIS ON ITS NORTH SIDE...THE SHEAR IS LIKELY TO DECREASE ENOUGH TO ALLOW ERNESTO TO STRENGTHEN. THE INTENSITY FORECAST THUS CALLS FOR SLOW STRENGTHENING FOR THE FIRST 24-36 HR...WITH SOMEWHAT FASTER STRENGTHENING THEREAFTER. THE NEW FORECAST CALLS FOR MORE STRENGTHENING OVER THE GULF OF MEXICO THAN PREVIOUSLY FORECAST DUE TO THE FORECAST UPPER-LEVEL WINDS AT 96 AND 120 HR. ALTHOUGH THE SHIPS AND SUPERENSEMBLE GUIDANCE CALLS FOR LITTLE CHANGE IN STRENGTH AFTER 96 HR...THERE IS A CHANCE THAT ERNESTO COULD BE MUCH STRONGER THAN CURRENTLY FORECAST OVER THE GULF OF MEXICO. FORECAST POSITIONS AND MAX WINDS INITIAL 25/2100Z 14.3N 67.6W 35 KT 12HR VT 26/0600Z 15.0N 69.7W 35 KT 24HR VT 26/1800Z 16.0N 72.2W 40 KT 36HR VT 27/0600Z 17.0N 74.7W 45 KT 48HR VT 27/1800Z 18.0N 77.2W 55 KT...OVER JAMAICA 72HR VT 28/1800Z 20.5N 82.0W 65 KT...OVER WATER 96HR VT 29/1800Z 23.0N 85.5W 70 KT 120HR VT 30/1800Z 24.5N 88.0W 75 KT |
