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| #145699 (Received by flhurricane at: 11:05 AM 13.Aug.2007) TCDAT4 TROPICAL DEPRESSION FOUR DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042007 1100 AM EDT MON AUG 13 2007 METEOSAT-9 VISIBLE AND INFRARED IMAGERY DURING THE PAST SEVERAL HOURS REVEALS THAT THE LOW PRESSURE AREA OVER THE FAR EASTERN TROPICAL ATLANTIC HAS BECOME A TROPICAL DEPRESSION. THE DEEP CONVECTION HAS BEEN PERSISTENT FOR MORE THAN 12 HOURS...BUT IT IS MOSTLY CONFINED WEST OF THE CIRCULATION CENTER DUE TO MODERATE EASTERLY WIND SHEAR. A QUIKSCAT OVERPASS AT 0723Z THIS MORNING ONLY CAPTURED THE EASTERN SEMICIRCLE BUT AN AMBIGUITY ANALYSIS INDICATES SOME BELIEVABLE 30-KT WINDS. DVORAK INTENSITY ESTIMATES BASED ON THE CURVED BAND PATTERN AT 12Z WERE 25-30 KT...ALTHOUGH THE DEPTH AND COVERAGE OF CONVECTION HAVE DECREASED SINCE 12Z. THE ADVISORY INTENSITY IS SET TO 30 KT. THE LOW-LEVEL CENTER HAS BEEN MOVING SLIGHTLY SOUTH OF DUE WEST THIS MORNING...AND THE INITIAL MOTION ESTIMATE IS 265/18...BUT MORE RECENT VISIBLE AND MICROWAVE IMAGES SUGGEST THE CENTER MIGHT BE EVEN A LITTLE FARTHER SOUTH THAN THE ADVISORY POSITION. WITH THE DEEP-LAYER RIDGE NORTH OF THE CYCLONE FORECAST TO STRENGTHEN AND BUILD WESTWARD...A SLIGHT SOUTHWARD COMPONENT OF MOTION MIGHT PERSIST FOR A COUPLE OF DAYS...BUT THE TRACK SHOULD BE GENERALLY WESTWARD AND FAIRLY BRISK. A VERY GRADUAL BEND TO THE RIGHT AND A SLIGHTLY SLOWER FORWARD SPEED ARE FORECAST TO BEGIN ON DAY THREE AS THE RIDGE WEAKENS...BUT ONLY SLIGHTLY. THE OFFICIAL FORECAST TRACK IS A BLEND OF THE GFDL...UKMET...AND GFS. THE EASTERLY WIND SHEAR WILL PROBABLY LIMIT INTENSIFICATION DURING THE NEXT COUPLE OF DAYS. THEREAFTER...THE GLOBAL MODELS...EVEN THOSE THAT DO NOT HAVE A STRONG REPRESENTATION OF THE TROPICAL CYCLONE ITSELF...FORECAST AN UPPER-LEVEL RIDGE TO BUILD OVER AND NEAR THE LESSER ANTILLES. COMBINED WITH WARM SEA-SURFACE TEMPERATURES ALONG THE TRACK...CONDITIONS APPEAR CONDUCIVE FOR STEADY STRENGTHENING LATER IN THE FORECAST PERIOD. THE SHIPS GUIDANCE FORECASTS NEARLY HURRICANE STRENGTH BY 72 HOURS...AND THE GFDL FORECAST INTENSITY EXCEEDS 100 KT AT FIVE DAYS. THE OFFICIAL FORECAST IS CLOSE TO THE SHIPS GUIDANCE FOR THE FIRST THREE DAYS...THEN INDICATES A STRENGTHENING HURRICANE...BUT IS NOT AS AGGRESSIVE AS THE GFDL. IT IS IMPORTANT TO REMEMBER THAT SIGNIFICANT UNCERTAINTIES EXIST IN BOTH THE TRACK AND INTENSITY FORECASTS...ESPECIALLY AT LONG RANGES. FORECAST POSITIONS AND MAX WINDS INITIAL 13/1500Z 12.0N 31.6W 30 KT 12HR VT 14/0000Z 12.0N 34.3W 35 KT 24HR VT 14/1200Z 11.9N 38.0W 40 KT 36HR VT 15/0000Z 11.9N 41.4W 45 KT 48HR VT 15/1200Z 11.9N 44.7W 50 KT 72HR VT 16/1200Z 13.0N 51.0W 60 KT 96HR VT 17/1200Z 14.5N 57.5W 75 KT 120HR VT 18/1200Z 16.0N 63.5W 90 KT $$ FORECASTER KNABB |
