000 WTNT41 KNHC 080900 TCDAT1 HURRICANE IDA DISCUSSION NUMBER 17 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112009 300 AM CST SUN NOV 08 2009 DATA FROM THE AIR FORCE HURRICANE HUNTER AIRCRAFT SUGGEST THAT THE INTENSIFICATION OF IDA HAS HALTED...AT LEAST TEMPORARILY. THE LATEST PRESSURE MEASURED ON A PASS THROUGH THE CENTER WAS 984 MB...AND THE INITIAL INTENSITY IS HELD AT 80 KT FOR THIS ADVISORY. THE INTENSITY FORECAST SHOWS SOME STRENGTHENING IN THE SHORT TERM...AS IDA WILL REMAIN OVER VERY WARM WATERS THROUGH THE NEXT 24 HOURS. BEYOND THAT TIME...IDA WILL BEGIN TO MOVE OVER MUCH COOLER WATERS...BELOW 26C AFTER 48 HOURS...AND VERTICAL SHEAR WILL INCREASE MARKEDLY AS STRONG UPPER-LEVEL SOUTHWESTERLY FLOW AHEAD OF A MID- TO UPPER-LEVEL TROUGH IMPINGES ON IDA. GLOBAL MODEL GUIDANCE SHOWS IDA UNDERGOING EXTRATROPICAL TRANSITION IN THE 48 TO 72 HOUR TIME FRAME AS IT INTERACTS WITH THE TROUGH AND A SURFACE FRONT ALONG THE NORTHERN GULF COAST. THE OFFICIAL FORECAST SHOWS GRADUAL WEAKENING FROM 24 TO 48 HOURS...AND MORE RAPID WEAKENING AS IDA BECOMES EXTRATROPICAL. THE INITIAL MOTION ESTIMATE IS NORTHWEST...OR 325/10. THIS IS TO THE LEFT OF THE PREVIOUS PACKAGE...AS THE FLOW AROUND A MID- TO UPPER-LEVEL TROUGH OVER SOUTHERN MEXICO AND GUATEMALA MAY BE TUGGING IDA A LITTLE MORE TOWARD THE WEST. THE TRACK GUIDANCE IS IN GOOD AGREEMENT ON A TURN TOWARD THE NORTH-NORTHWEST AND THE NORTH OVER THE NEXT 48 HOURS AS IDA ACCELERATES AHEAD OF THE TROUGH THAT MOVES INTO THE NORTHERN GULF. GIVEN THE MORE WESTERLY COMPONENT OF THE INITIAL MOTION...THE TRACK GUIDANCE HAS SHIFTED WESTWARD COMPARED TO THE LAST PACKAGE...AND SO HAS THE OFFICIAL FORECAST... WHICH NOW TAKES THE CENTER OF IDA VERY CLOSE TO THE NORTHEASTERN TIP OF THE YUCATAN PENINSULA TODAY. IDA WILL THEN MOVE INTO THE GULF OF MEXICO AND APPROACH THE EAST-CENTRAL GULF COAST IN 48 TO 72 HOURS. MOST OF THE TRACK GUIDANCE SHOWS A TURN TOWARD THE EAST AND SOUTHEAST AT DAYS 3 AND 4 AS IDA BECOMES EXTRATROPICAL. HOWEVER... THERE IS LARGE SPREAD IN THE GUIDANCE WITH REGARD TO THE ULTIMATE FATE OF IDA. FOR EXAMPLE...THE ECMWF SHOWS THE EXTRATROPICAL REMNANTS OF IDA CONTINUING ACROSS THE SOUTHEASTERN UNITED STATES...WHILE THE GFS LEAVES THE REMNANTS OF IDA BEHIND A STRONGER BAROCLINIC LOW THAT FORMS OVER THE SOUTHEASTERN UNITED STATES. GIVEN THE LARGE RANGE OF POSSIBLE SOLUTIONS...THE OFFICIAL FORECAST SHOWS A SLOW SOUTHEASTWARD MOTION AT DAY 4...AND HAS IDA DISSIPATING AS IT IS ABSORBED INTO A FRONTAL ZONE BY DAY 5. THERE IS A HIGH DEGREE OF UNCERTAINTY IN THIS PART OF THE FORECAST SCENARIO. THE OFFICIAL FORECAST SHOWS TROPICAL STORM FORCE WINDS REACHING PORTIONS OF THE U.S. GULF COAST IN A COUPLE OF DAYS. HOWEVER... SINCE IDA IS EXPECTED TO BEGIN UNDERGOING EXTRATROPICAL TRANSITION AROUND THAT TIME...THESE HAZARDS 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 08/0900Z 20.5N 85.6W 80 KT 12HR VT 08/1800Z 21.8N 86.7W 85 KT 24HR VT 09/0600Z 24.0N 87.8W 85 KT 36HR VT 09/1800Z 26.7N 88.5W 80 KT 48HR VT 10/0600Z 28.5N 88.2W 65 KT 72HR VT 11/0600Z 29.8N 86.1W 45 KT...EXTRATROPICAL 96HR VT 12/0600Z 28.0N 84.0W 30 KT...EXTRATROPICAL 120HR VT 13/0600Z...DISSIPATED $$ FORECASTER BRENNAN/KIMBERLAIN