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| #46831 (Received by flhurricane at: 11:08 PM 18.Sep.2005) TCDAT3 TROPICAL STORM RITA DISCUSSION NUMBER 5 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT SUN SEP 18 2005 THE LAST RECON REPORT AT 17/2324Z INDICATED MAXIMUM RELIABLE 850 MB FLIGHT-LEVEL WINDS OF ABOUT 55 KT...OR ROUGHLY 44 KT SURFACE WINDS. THERE WAS ONE FLIGHT-LEVEL REPORT OF 67 KT...BUT THIS OCCURRED DURING CLIMBOUT TO A HIGHER ALTITUDE TO AVOID TURBULENCE...AND IS THEREFORE NOT DEEMED REPRESENTATIVE OF THE ACTUAL WIND FIELD. SINCE THE LAST RECON FLIGHT...CLOUD TOPS HAVE WARMED NEAR THE CIRCULATION CENTER...SO THE INTENSITY IS BEING HELD AT 45 KT. THE INITIAL MOTION ESTIMATE IS 300/09. RITA HAS ACTUALLY BEEN MOVING OR PROPAGATING NORTHWESTWARD THE PAST 6 TO 9 HOURS. THIS MOTION MAY BE DUE TO THE CENTER REFORMING CLOSER TO THE DEEP CONVECTION...OR ACTUAL MOVEMENT TOWARD A WEAKER BREAK IN THE MID-LEVEL RIDGE LOCATED ALONG 75W LONGITUDE. ALSO...AN UPPER-LEVEL LOW PREVIOUSLY LOCATED NEAR JAMAICA HAS MOVED NORTHWESTWARD TO NEAR CAYMAN BRAC AND HAS NOT WEAKENED LIKE THE GLOBAL MODELS HAVE BEEN FORECASTING. THE COMBINATION OF THE SOUTHEASTERLY FLOW ON THE EAST SIDE OF UPPER LOW...COMBINED WITH THE SOUTHEASTERLY FLOW ON THE SOUTHWEST SIDE OF A LARGE MID-LEVEL RIDGE LOCATED EAST OF BERMUDA...SHOULD STEER RITA IN A GENERAL WEST-NORTHWESTWARD MOTION FOR THE NEXT 12 TO PERHAPS 24 HOURS. AFTER THAT...ALL OF THE GLOBAL AND REGIONAL MODELS AGREE THAT THE LARGE MID-LEVEL RIDGE THAT EXTENDS ALONG THE GULF COAST FROM A HIGH CENTER OVER LOUISIANA WILL GRADUALLY BUILD EASTWARD AND TURN RITA WESTWARD. HOWEVER...THE SAME MODELS ALSO AGREE THAT THE HEIGHTS WILL NOT INCREASE ACROSS SOUTHERN FLORIDA AND...IN FACT... HEIGHTS FROM 700 MB TO 400 MB HAVE NOT INCREASED ACROSS SOUTH FLORIDA DURING THE PAST 24 HOURS...BUT THE WIND SPEEDS HAVE DECREASED. THIS ALL SUGGESTS THAT THE EASTERN EXTENT OF THE RIDGE EAST OF FLORIDA MAY NOT BE AS STRONG AS INDICATED IN THE MODEL FIELDS. AS SUCH...THERE MAY A NORTHWARD SHIFT IN THE MODEL GUIDANCE TRACKS IN THE 00Z MODEL RUNS. HOWEVER...WITH SUCH A LARGE AND STRONG RIDGE IN PLACE ACROSS THE GULF COAST...RITA SHOULD GRADUALLY EVENTUALLY MOVE WESTWARD ACROSS THE CENTRAL GULF AND INTO THE WESTERN GULF OF MEXICO BY THE END OF THE PERIOD. THE OFFICIAL TRACK WAS SHIFTED TO THE RIGHT OF THE PREVIOUS FORECAST TO ACCOUNT FOR THE MORE NORTHWARD INITIAL POSITION. THIS NORTHWARD SHIFT HAS REQUIRED THE PREVIOUS WATCHES FOR THE FLORIDA KEYS AND SOUTH FLORIDA TO BE UPGRADED TO HURRICANE AND TROPICAL STORM WARNINGS. THE VERTICAL SHEAR IS NOW FORECAST BY ALL OF THE MODELS TO GRADUALLY DECREASE FROM THE CURRENT 15 KT DOWN TO LESS THAN 5 KT BY 36-72 HOURS. THIS SHOULD ALLOW FOR SOME SIGNIFICANT STRENGTHENING TO COCUR...ESPECIALLY SINCE RITA WILL BE OVER 30C SSTS AND IMPRESSIVE POLEWARD OUTFLOW PATTERN WILL BE MAINTAINED. THE OFFICIAL INTENSITY FORECAST FOLLOWS THE TREND OF THE SHIPS...GFDL...AND FSU SUPER ENSEMBLE MODELS...WHICH ALL BRING THE CYCLONE TO MAJOR HURRICANE STRENGTH...AT LEAST 100 KT...BY 72 HOURS. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 19/0300Z 22.9N 73.3W 45 KT 12HR VT 19/1200Z 23.4N 75.1W 50 KT 24HR VT 20/0000Z 24.1N 77.5W 60 KT 36HR VT 20/1200Z 24.3N 80.1W 75 KT 48HR VT 21/0000Z 24.2N 83.0W 90 KT 72HR VT 22/0000Z 24.1N 88.5W 100 KT 96HR VT 23/0000Z 24.5N 92.0W 100 KT 120HR VT 24/0000Z 26.5N 95.5W 100 KT |
