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| #306950 (Received by flhurricane at: 3:52 PM 08.Nov.2009) TCDAT1 HURRICANE IDA DISCUSSION NUMBER 20 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112009 300 PM CST SUN NOV 08 2009 REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE THAT THE CENTRAL PRESSURE OF IDA HAS FALLEN TO 976 MB. THE AIRCRAFT REPORTED MAXIMUM 700 MB FLIGHT-LEVEL WINDS OF 94 KT...WITH SFMR ESTIMATES OF 80-85 KT. BASED ON THIS...THE INITIAL INTENSITY IS 85 KT. SATELLITE IMAGERY AND RADAR DATA FROM MEXICO AND CUBA SUGGEST THAT THE EYEWALL HAS BECOME LESS ORGANIZED DURING THE PAST FEW HOURS...WHICH MAY BE A SIGN THAT IDA IS BEING AFFECTED BY ONGOING SOUTHWESTERLY VERTICAL WIND SHEAR. THE INITIAL MOTION IS 330/9. IDA REMAINS BETWEEN A MID/UPPER-LEVEL TROUGH OVER THE WESTERN GULF MEXICO AND ADJACENT LAND AREAS AND AN MID/UPPER-LEVEL RIDGE OVER THE EASTERN GULF OF MEXICO AND THE NORTHERN CARIBBEAN SEA. IN ADDITION...A STRONG LOW-LEVEL RIDGE COVERS THE NORTHERN GULF OF MEXICO. THE DYNAMICAL MODELS FORECAST THE TROUGH AND RIDGE TO MOVE EASTWARD...ALLOWING IDA TO TURN TOWARD THE NORTH DURING THE NEXT 36 HR OR SO. ALTHOUGH THE TRACK GUIDANCE AGREES WITH THIS SCENARIO...THERE IS CONSIDERABLE SPREAD IN BOTH THE LOCATION AND TIMING OF THE MODELS FORECAST LANDFALLS ON THE NORTHERN GULF COAST. THE ECMWF AND CANADIAN MODELS ARE ON THE WESTERN EDGE OF THE ENVELOPE WITH A SOUTHEASTERN LOUISIANA LANDFALL. THE HWRF IS ON THE EASTERN EDGE WITH A LANDFALL IN THE WESTERN FLORIDA PANHANDLE. THE UKMET IS NOTABLE SLOWER THAN THE OTHER GUIDANCE...CALLING FOR A LANDFALL AFTER 48 HR. THE NEW FORECAST TRACK COMPROMISES BETWEEN THESE EXTREMES AND LIES NEAR THE VARIOUS CONSENSUS MODELS. AFTER LANDFALL...THE MODEL SPREAD GETS VERY LARGE DUE TO MAJOR MODEL DIFFERENCES ON THE EVOLUTION OF THE WESTERLIES OVER THE SOUTHEASTERN UNITED STATES. THE NEW TRACK CALLS FOR A SLOW EASTWARD MOTION...BUT THIS PART OF THE TRACK IS LOW CONFIDENCE. THE HURRICANE MAY BE ABLE TO STRENGTHEN A LITTLE MORE IN THE NEXT 6-12 HR. AFTER THAT...IDA WILL BE MOVING OVER COOLER SEA SURFACE TEMPERATURES...INTO A COOLER AIR MASS...AND INTO STRONGER SHEAR. WHILE EXTRATROPICAL TRANSITION SHOULD BEGIN BEFORE IDA MAKES LANDFALL...IT IS UNCERTAIN IF THE CYCLONE WILL COMPLETELY LOSE ITS TROPICAL CHARACTERISTICS BEFORE LANDFALL. IN ADDITION...MOST OF THE INTENSITY GUIDANCE FORECAST IDA TO MAINTAIN HURRICANE STRENGTH UNTIL LANDFALL ON THE NORTHERN GULF COAST. BASED ON THIS...THE NEW INTENSITY FORECAST MAINTAINS IDA AS A WEAKENING HURRICANE THROUGH LANDFALL...THEN FORECASTS EXTRATROPICAL TO FINISH AFTER LANDFALL. IN THE 72-120 HR TIME FRAME...THE GFS...ECMWF...AND CANADIAN MODELS FORECAST A LARGE BAROCLINIC LOW OFF THE U. S. EAST COAST. IT IS NOT CLEAR WHETHER THIS IS THE REMAINS OF IDA OR A SECOND LOW THAT ABSORBS IDA. THE FORECAST CONTINUES TO USE THE SCENARIO THAT THIS IS A SECOND LOW THAT ABSORBS THE REMAINS OF IDA. THE UNCERTAINTY OVER THE TIMING OF EXTRATROPICAL TRANSITION REQUIRES A HURRICANE WATCH FOR PORTIONS OF THE NORTHERN GULF COAST. REGARDLESS OF WHETHER IDA LOSES ITS TROPICAL CHARACTERISTICS BEFORE LANDFALL...THE CYCLONE IS EXPECTED TO BRING STRONG WINDS...HEAVY RAINS...AND STORM SURGES TO THAT AREA. OUTSIDE OF THE HURRICANE WATCH AREA....POTENTIAL HAZARDS ASSOCIATED WITH IDA ARE BEING HANDLED BY LOCAL NATIONAL WEATHER SERVICE OFFICES ALONG THE GULF COAST IN THEIR PRODUCT SUITE WITH MARINE AND COASTAL FLOOD WATCHES...WARNINGS...AND ADVISORIES. FORECAST POSITIONS AND MAX WINDS INITIAL 08/2100Z 22.2N 86.3W 85 KT 12HR VT 09/0600Z 23.9N 87.4W 85 KT 24HR VT 09/1800Z 26.7N 88.0W 85 KT 36HR VT 10/0600Z 29.2N 87.9W 75 KT 48HR VT 10/1800Z 30.7N 86.7W 55 KT...EXTRATROPICAL INLAND 72HR VT 11/1800Z 31.0N 83.0W 40 KT...EXTRATROPICAL INLAND 96HR VT 12/1800Z 30.0N 79.5W 40 KT...EXTRATROPICAL 120HR VT 13/1800Z...ABSORBED BY EXTRATROPICAL LOW $$ FORECASTER BEVEN |
