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| #46793 (Received by flhurricane at: 5:11 PM 18.Sep.2005) TCDAT3 TROPICAL STORM RITA DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT SUN SEP 18 2005 THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT DID NOT FIND A VERY IMPRESSIVE WIND FIELD JUST ABOVE THE SURFACE NEAR THE CENTER OF CIRCULATION... BUT DID RECENTLY MEASURE A CENTRAL PRESSURE OF 1005 MB AND MAXIMUM FLIGHT LEVEL WINDS OF 45 KT... WELL TO THE NORTHEAST OF THE CENTER. ADDITIONALLY... SHIP OBSERVATIONS FROM WELL TO THE NORTH AND EAST OF THE CENTER HAVE INDICATED WINDS OF 30-35 KT DURING THE PAST SEVERAL HOURS. THESE DATA... COMBINED WITH DVORAK INTENSITY ESTIMATES OF 30-35 KT SUPPORT UPGRADING THE SYSTEM TO A TROPICAL STORM WITH 35 KT WINDS. THE LACK OF WIND NEAR THE CENTER IS NOT SURPRISING GIVEN THAT ALL OF THE CONVECTION AND PERHAPS A MID LEVEL CIRCULATION CENTER ARE DISPLACED TO THE NORTH... DUE TO SOUTHERLY SHEAR CAUSED BY THE UPPER-LEVEL LOW OVER EASTERN CUBA. THE TROPICAL STORM IS STILL IN THE PROCESS OF ORGANIZING. IT HAS A FAIRLY LARGE CIRCULATION AND SOME DEEP CONVECTION WITH TOPS COLDER THAN -70C... AND WHILE UPPER-LEVEL OUTFLOW IS RESTRICTED TO THE SOUTHWEST DUE TO THE SHEAR... IT IS BECOMING WELL ESTABLISHED IN THE REMAINING THREE QUADRANTS. SINCE DYNAMICAL MODELS FORECAST THE UPPER LOW TO WEAKEN AND ALLOW AN UPPER RIDGE TO BUILD IN ITS PLACE OVER FLORIDA AND THE NORTHERN BAHAMAS...ATMOSPHERIC CONDITIONS ARE EXPECTED TO GRADUALLY BECOME MORE CONDUCIVE FOR STRENGTHENING. WHILE THE GFDL STILL DOES NOT FORECAST DEVELOPMENT UNTIL RITA REACHES THE GULF OF MEXICO... THE SHIPS GUIDANCE FORECAST OF 64 KT BY 48 HOURS SEEMS MORE LIKELY. THE NEW OFFICIAL INTENSITY FORECAST IS BASICALLY AN UPDATE OF THE PREVIOUS ADVISORY...ANTICIPATING A HURRICANE IN 36-48 HOURS. ADDITIONAL DEVELOPMENT IS FORECAST ONCE THE STORM REACHES THE GULF OF MEXICO. THE INITIAL AND FORECAST MOTION ARE COMPLICATED BY THE ASYMMETRIC CLOUD PATTERN...WHICH SEEM TO WANT TO DRAG THE SYSTEM NORTH OF A DUE WEST TRACK...WHILE A MID LEVEL RIDGE TO THE NORTH OF THE CYCLONE IS TRYING TO FORCE THE SYSTEM DUE WESTWARD. THESE FACTORS WILL CONTINUE TO BATTLE FOR THE NEXT DAY OR SO UNTIL THE SHEAR RELAXES. THE DYNAMICAL MODELS HAVE SHIFTED FARTHER SOUTH IN TAKING THE SYSTEM THROUGH THE FLORIDA STRAITS...IN SOME CASES SOUTH OF DUE WEST...TOWARD THE GULF OF MEXICO. THE OFFICIAL FORECAST IS ONLY ADJUSTED SLIGHTLY SOUTHWARD SINCE IT IS QUITE POSSIBLE THE CENTER WILL REFORM FARTHER NORTH DURING THE NEXT 36 HOURS. FORECASTER KNABB FORECAST POSITIONS AND MAX WINDS INITIAL 18/2100Z 22.2N 72.7W 35 KT 12HR VT 19/0600Z 22.6N 74.7W 45 KT 24HR VT 19/1800Z 23.2N 77.3W 50 KT 36HR VT 20/0600Z 23.5N 79.7W 60 KT 48HR VT 20/1800Z 23.5N 82.5W 70 KT 72HR VT 21/1800Z 23.5N 87.5W 75 KT 96HR VT 22/1800Z 24.0N 91.5W 85 KT 120HR VT 23/1800Z 25.5N 95.0W 95 KT |
