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| #306670 (Received by flhurricane at: 10:03 AM 07.Nov.2009) TCDAT1 TROPICAL STORM IDA DISCUSSION NUMBER 13 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112009 1000 AM EST SAT NOV 07 2009 RECENT MICROWAVE IMAGERY SUGGESTS THAT THE STRUCTURE OF IDA HAS CONTINUED TO IMPROVE THIS MORNING...WITH A COUPLE OF HOOKING BANDS NEAR THE CENTER. VISIBLE IMAGERY SHOWS AN EXPANDING CENTRAL DENSE OVERCAST FEATURE AND NO OBVIOUS SIGNS OF SIGNIFICANT SHEAR. THE LATEST DVORAK INTENSITY ESTIMATES ARE 45 KT FROM BOTH AGENCIES...BUT GIVEN THE INCREASE IN ORGANIZATION SINCE THAT TIME THE INITIAL INTENSITY HAS BEEN RAISED TO 50 KT. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS CURRENTLY EN ROUTE TO INVESTIGATE THE STORM. IDA IS MOVING NORTHWARD OR 355/8. IDA IS EXPECTED TO MOVE NORTH-NORTHWESTWARD BETWEEN A MID-LEVEL ANTICYCLONE OVER THE NORTH-CENTRAL CARIBBEAN SEA AND A DEEP-LAYER TROUGH OVER SOUTHERN MEXICO. THE TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH 36 TO 48 HOURS AND THE NHC FORECAST REMAINS IN LINE WITH THE MODEL CONSENSUS DURING THAT TIME. THEREAFTER...THERE IS A LARGE SPREAD AMONG THE MODELS AS TO HOW IDA INTERACTS WITH A MID- TO UPPER-LEVEL TROUGH DIGGING INTO THE NORTHERN GULF OF MEXICO. THE GFS...ECMWF...AND HWRF ALL MOVE THE CYCLONE QUICKLY NORTHWARD AND SHOW IT REACHING THE NORTHERN GULF COAST IN ABOUT 3 DAYS AS IT BECOMES AN EXTRATROPICAL CYCLONE. THE REMAINDER OF THE GUIDANCE HAS TRENDED NORTHWARD...BUT TURNS THE SYSTEM GENERALLY EASTWARD BEFORE REACHING THE NORTHERN GULF COAST. FOR NOW...THE OFFICIAL FORECAST IS BETWEEN THESE TWO SCENARIOS...BUT HAS BEEN ADJUSTED NORTHWARD TO ACCOUNT FOR THE LATEST TRENDS. ENVIRONMENTAL CONDITIONS...WHILE NOT IDEAL...APPEAR CONDUCIVE ENOUGH FOR STRENGTHENING DURING THE NEXT DAY OR SO AS THE CYCLONE TRAVERSES THE NORTHWEST CARIBBEAN SEA. THE OFFICIAL FORECAST HAS BEEN ADJUSTED UPWARD FROM THE PREVIOUS ONE BASED ON RECENT TRENDS. ONCE IDA REACHES THE GULF OF MEXICO...SHEAR IS FORECAST TO INCREASE AND WATERS BEGIN TO COOL. THESE FACTORS SHOULD CONTRIBUTE TO WEAKENING...HOWEVER THE INTERACTION WITH THE UPPER-TROUGH AND AN EXPECTED EXTRATROPICAL TRANSITION WILL LIKELY RESULT IN LESS WEAKENING THAN TYPICAL...GIVEN THE STRONG SHEAR. MOST OF THE GLOBAL MODELS SHOW A LARGE PRESSURE GRADIENT BETWEEN A HIGH PRESSURE RIDGE OVER THE SOUTHEASTERN UNITED STATES AND THE TROPICAL CYCLONE. THIS IS ALREADY CONTRIBUTING TO A LARGE AREA OF STRONG WINDS OVER THE SOUTHERN GULF OF MEXICO WHICH IS NOT DIRECTLY ATTRIBUTABLE TO IDA. FORECAST POSITIONS AND MAX WINDS INITIAL 07/1500Z 17.9N 84.1W 50 KT 12HR VT 08/0000Z 18.9N 84.6W 55 KT 24HR VT 08/1200Z 20.3N 85.5W 60 KT 36HR VT 09/0000Z 22.2N 86.8W 55 KT 48HR VT 09/1200Z 24.6N 88.0W 45 KT 72HR VT 10/1200Z 28.5N 88.0W 45 KT...EXTRATROPICAL 96HR VT 11/1200Z 29.0N 86.5W 40 KT...EXTRATROPICAL 120HR VT 12/1200Z 28.0N 85.0W 35 KT...EXTRATROPICAL $$ FORECASTER BROWN/CANGIALOSI/BLAKE |
