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| #57523 (Received by flhurricane at: 10:11 PM 18.Nov.2005) TCDAT2 TROPICAL STORM GAMMA DISCUSSION NUMBER 13 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 10 PM EST FRI NOV 18 2005 THE AIR FORCE HURRICANE HUNTER AIRCRAFT... ON ITS LAST LEG ALONG THE NORTH-CENTRAL COAST OF HONDURAS EARLIER THIS EVENING JUST BEFORE 22Z... DID NOT MEASURE ANY WESTERLY WINDS. HOWEVER... SATELLITE IMAGERY AND SURFACE OBSERVATIONS IN HONDURAS SUGGESTED WESTERLY WINDS FARTHER SOUTH... SO THE LOW-LEVEL CENTER APPEARS TO HAVE BEEN ALONG THE IMMEDIATE COAST AT THAT TIME. MORE RECENT IMAGERY SUGGESTS THE LOW-LEVEL CENTER HAS EDGED NORTHWESTWARD OFF THE COAST AT A FORWARD SPEED OF ABOUT 4 KT. A MID-LEVEL CENTER IS APPARENT IN THE COLDER INFRARED TOPS FARTHER NORTH... WITH THE TILTING LIKELY CAUSED BY THE SOUTHERLY WIND SHEAR. ALSO ON ITS LAST LEG... THE AIRCRAFT MEASURED 1500-FT FLIGHT-LEVEL WINDS OF 56 KT. 00Z DVORAK INTENSITY ESTIMATES BASED ON THE CURVED BANDING IN THE MID-LEVELS ARE ONLY 30 KT... BUT A SHEAR PATTERN USING A MORE SOUTHERN CENTER LOCATION YIELDS A STRONGER ESTIMATE. THE ADVISORY INTENSITY IS SET TO 40 KT MAINLY BASED ON THE EARLIER AIRCRAFT DATA... BUT IT IS ALSO CONSISTENT WITH A 2330Z QUIKSCAT PASS. THE DYNAMICAL MODELS ARE UNANIMOUS IN FORECASTING AN EXTRATROPICAL LOW PRESSURE SYSTEM TO FORM OVER THE SOUTHEASTERN UNITED STATES IN A LITTLE MORE THAN TWO DAYS... IN ASSOCIATION WITH A DEVELOPING MID-LATITUDE TROUGH OVER THE EASTERN HALF OF THE U.S. THE MODELS ARE NOT IN AGREEMENT... HOWEVER... ON WHAT WILL BE LEFT OF GAMMA BY THAT TIME. MOST OF THEM FORECAST A TRACK THAT SEEMS TOO FAR TO THE WEST OVER YUCATAN AND TOO SLOW... GIVEN THE SOUTHERLY MID- TO UPPER-LEVEL FLOW THAT WILL LIKELY DRAG GAMMA MORE NORTHWARD OVER THE WESTERN CARIBBEAN SEA... WHILE SHEARING THE SYSTEM AND FORCING THE LOW-LEVEL CENTER TO STAY CLOSER TO THE CONVECTION. THE MODELS OFTEN DO NOT FORECAST THE TRACK WELL FOR SHEARED SYSTEMS... AND THE OFFICIAL FORECAST LEANS CLOSER TO THE DIRECTION IN WHICH THE SHEAR IS POINTED. BEYOND ABOUT 48 HOURS... ONCE THE EXTRATROPICAL SYSTEM FORMS OVER THE SOUTHEASTERN U.S... THE NEW OFFICIAL FORECAST... LIKE THE PREVIOUS ADVISORY... KEEPS GAMMA MOVING ALONG WITH THAT SYSTEM EVEN THOUGH MOST OF THE MODELS ARE MUCH SLOWER. THE WIND SHEAR WILL ONLY GET STRONGER AS THE TROUGH DEVELOPS OVER THE SOUTHEASTERN U.S. AND GULF OF MEXICO DURING THE NEXT 2-3 DAYS. THEREFORE... CONDITIONS DO NOT APPEAR CONDUCIVE FOR SIGNIFICANT STRENGTHENING... AND INTENSIFICATION TO A HURRICANE SEEMS RATHER UNLIKELY IN THIS ENVIRONMENT. THE GFDL NOW FORECASTS LITTLE CHANGE IN THE INTENSITY FOR THE NEXT 2-3 DAYS AND PEAKS AT ABOUT 45 KT. THE SHIPS IS SIMILAR BUT FORECASTS A DECLINE AFTER 24 HOURS AS THE SHEAR INCREASES. THE OFFICIAL INTENSITY FORECAST IS ADJUSTED DOWNWARD COMPARED TO THE PREVIOUS ADVISORY... ANTICIPATING THE POSSIBILITY OF SOME SLIGHT STRENGTHENING IN THE SHORT TERM BUT OVERALL LITTLE CHANGE UNTIL GAMMA BECOMES EXTRATROPICAL AND EVENTUALLY IS ABSORBED INTO THE LARGER EXTRATROPICAL SYSTEM OVER THE ATLANTIC. FORECASTER KNABB FORECAST POSITIONS AND MAX WINDS INITIAL 19/0300Z 16.4N 85.8W 40 KT 12HR VT 19/1200Z 16.8N 86.3W 45 KT 24HR VT 20/0000Z 17.4N 86.9W 45 KT 36HR VT 20/1200Z 18.8N 87.0W 45 KT 48HR VT 21/0000Z 20.8N 85.6W 45 KT 72HR VT 22/0000Z 25.0N 81.0W 45 KT 96HR VT 23/0000Z 34.0N 70.0W 40 KT...EXTRATROPICAL 120HR VT 24/0000Z...ABSORBED BY LARGER EXTRATROPICAL SYSTEM |
