000 WTNT41 KNHC 081516 TCDAT1 HURRICANE IDA DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112009 900 AM CST SUN NOV 08 2009 THE LAST PASS OF AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT NEAR 1100 UTC SHOWED A CENTRAL PRESSURE OF 983 MB AND AN ELLIPTICAL EYE. SATELLITE IMAGERY AND RADAR DATA FROM CUBA AND MEXICO SINCE THAT TIME SUGGEST LITTLE CHANGE HAS OCCURRED IN THE STRUCTURE. BASED ON THIS AND SATELLITE INTENSITY ESTIMATES OF 90 AND 77 KT FROM TAFB AND SAB...THE INITIAL INTENSITY REMAINS 80 KT. ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN INDICATE THAT THE HURRICANE IS CURRENTLY EXPERIENCING ABOUT 20 KT OF SOUTHWESTERLY VERTICAL WIND SHEAR. THE INITIAL MOTION IS 325/9. 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. THE GFDL...HWRF...GFS... ECMWF...AND CANADIAN MODELS ARE NOW FORECASTING A FASTER NORTHWARD MOTION...WITH THE CENTER OF IDA REACHING THE NORTHERN GULF COAST IN 36-48 HR. THE UKMET AND NOGAPS MODELS CONTINUE TO SHOW A SLOWER FORWARD SPEED. THE NEW FORECAST TRACK IS FASTER THAN THE PREVIOUS TRACK THROUGH 48 HR...ALTHOUGH IT IS SLOWER THAN THE GFDL AND ITS COLLEAGUES. THE FASTER NORTHWARD MOTION ALSO RESULTS IN A MORE NORTHERLY POSITION FOR THE LATER PART OF THE FORECAST TRACK...SO THE 72-96 HR POSITIONS HAVE BEEN ADJUSTED NORTHWARD AS WELL. SOME STRENGTHENING IS POSSIBLE TODAY. AFTER THAT...IDA WILL BE MOVING OVER COOLER SEA SURFACE TEMPERATURES...INTO A COOLER AIR MASS...AND INTO STRONGER SHEAR. THE DYNAMICAL MODELS AGREE THAT EXTRATROPICAL TRANSITION SHOULD BEGIN BY ABOUT 24 HOURS AND IS LIKELY TO BE COMPLETE IN ABOUT 48 HR. HOWEVER...THE INTENSITY GUIDANCE FORECASTS HURRICANE-FORCE WINDS THROUGH 48 HR...SO THE INTENSITY FORECAST MAINTAINS HURRICANE STRENGTH THROUGH THAT TIME. 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. AT THIS TIME...THE FORECAST USES THE SCENARIO THAT THIS IS A SECOND LOW THAT ABSORBS THE REMAINS OF IDA. WHILE IT IS LIKELY THAT IDA WILL LOSE TROPICAL CYCLONE CHARACTERISTICS BEFORE REACHING THE NORTHERN GULF COAST...IT IS POSSIBLE THAT TROPICAL STORM- OR HURRICANE-FORCE WINDS COULD REACH PORTIONS OF THE COAST BEFORE EXTRATROPICAL TRANSITION IS COMPLETE. THUS...A HURRICANE WATCH HAS BEEN ISSUED FOR PORTIONS OF THE NORTHERN GULF COAST AT THIS TIME. OTHER POTENTIAL HAZARDS ASSOCIATED WITH IDA ARE...FOR NOW...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 08/1500Z 21.2N 86.0W 80 KT 12HR VT 09/0000Z 22.8N 87.1W 85 KT 24HR VT 09/1200Z 25.6N 88.4W 85 KT 36HR VT 10/0000Z 28.2N 88.6W 75 KT 48HR VT 10/1200Z 30.0N 87.8W 65 KT...EXTRATROPICAL 72HR VT 11/1200Z 30.5N 84.5W 40 KT...EXTRATROPICAL INLAND 96HR VT 12/1200Z 30.0N 81.0W 30 KT...EXTRATROPICAL 120HR VT 13/1200Z...ABSORBED BY EXTRATROPICAL LOW $$ FORECASTER BEVEN