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| #306607 (Received by flhurricane at: 3:59 AM 07.Nov.2009) TCDAT1 TROPICAL STORM IDA DISCUSSION NUMBER 12 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112009 400 AM EST SAT NOV 07 2009 THE SATELLITE PRESENTATION OF IDA HAS IMPROVED OVER THE PAST SEVERAL HOURS...WITH AN INCREASE IN DEEP CONVECTION NEAR THE ESTIMATED LOCATION OF THE LOW LEVEL CENTER. THE INITIAL INTENSITY IS RAISED TO 40 KT BASED ON A BLEND OF DVORAK ESTIMATES OF 35 KT FROM SAB AND 45 KT FROM TAFB. THE INITIAL MOTION ESTIMATE IS 350/07...A LITTLE FASTER THAN BEFORE. IDA IS MOVING NORTHWARD BETWEEN A MID-LEVEL ANTICYCLONE OVER THE NORTH-CENTRAL CARIBBEAN SEA AND A DEEP-LAYER TROUGH OVER SOUTHERN MEXICO. MOST OF THE TRACK GUIDANCE IS TIGHTLY CLUSTERED THROUGH 48 HOURS...AND THE OFFICIAL FORECAST THROUGH THAT TIME IS CLOSE TO THE MODEL CONSENSUS BUT A LITTLE FASTER THAN THE PREVIOUS PACKAGE. BEYOND 48 HOURS...THE GLOBAL MODELS SHOW A MID- TO UPPER-LEVEL SHORTWAVE TROUGH DIGGING INTO THE NORTHERN GULF OF MEXICO. WHILE THE DETAILS ON THE TIMING AND DEGREE OF THE INTERACTION BETWEEN IDA AND THE TROUGH DIFFER...MOST OF THE MODELS...WITH THE EXCEPTION OF THE NOGAPS AND GFDN...SHOW IDA TURNING NORTHWARD AND THEN NORTHEASTWARD IN 3 OR 4 DAYS. IDA IS EXPECTED TO BECOME EXTRATROPICAL DURING THIS TIME AS IT BECOMES INVOLVED WITH A LOW-LEVEL FRONTAL ZONE ALONG THE NORTHERN GULF COAST. BY DAY 5 MOST OF THE GUIDANCE SHOWS THE FRONT...AND WHAT IS LEFT OF IDA... TURNING SOUTHWARD OR SOUTHEASTWARD IN RESPONSE TO A LARGE SCALE MID- TO UPPER-LEVEL TROUGH AMPLIFYING OVER EASTERN NORTH AMERICA. AT DAYS 3 THROUGH 5 THE NEW OFFICIAL THE FORECAST IS ADJUSTED A LITTLE NORTHWARD TOWARD THE MODEL CONSENSUS. WHILE IDA WILL BE MOVING OVER VERY WARM WATERS FOR THE NEXT COUPLE OF DAYS THE ENVIRONMENT WILL NOT BE IDEAL FOR STRENGTHENING...AS THE SHIPS MODEL SHOWS ABOUT 20 KT OF VERTICAL SHEAR OVER THE CYCLONE. BEYOND THAT TIME...THE SHEAR IS FORECAST TO INCREASE FURTHER AS IDA BEGINS TO INTERACT WITH THE MID- TO UPPER-LEVEL SHORTWAVE. THE OFFICIAL FORECAST IS ADJUSTED UPWARD A LITTLE GIVEN THE OBSERVED INTENSITY TRENDS...AND SHOWS A PEAK OF 50 KT IN 36 HOURS. THIS IS IN BEST AGREEMENT WITH THE SHIPS MODEL AND CLOSE TO THE ICON INTENSITY CONSENSUS. GRADUAL WEAKENING IS EXPECTED TO BEGIN ON DAY 2 AS IDA ENCOUNTERS THE STRONGER SHEAR AND BEGINS TO UNDERGO EXTRATROPICAL TRANSITION. MOST OF THE GLOBAL MODELS SHOW A LARGE PRESSURE GRADIENT DEVELOPING BETWEEN A HIGH PRESSURE RIDGE OVER THE SOUTHEASTERN UNITED STATES AND THE TROPICAL CYCLONE. THIS WILL CONTRIBUTE TO A LARGE AREA OF STRONG WINDS OVER THE GULF OF MEXICO NOT DIRECTLY ATTRIBUTABLE TO IDA. THE ISSUANCE OF A TROPICAL STORM WATCH IS REQUIRED AT THIS TIME FOR PORTIONS OF THE YUCATAN PENINSULA AND WESTERN CUBA. FORECAST POSITIONS AND MAX WINDS INITIAL 07/0900Z 17.1N 84.1W 40 KT 12HR VT 07/1800Z 18.1N 84.4W 45 KT 24HR VT 08/0600Z 19.5N 85.0W 45 KT 36HR VT 08/1800Z 21.0N 86.0W 50 KT 48HR VT 09/0600Z 23.0N 87.1W 45 KT 72HR VT 10/0600Z 26.5N 88.0W 45 KT 96HR VT 11/0600Z 28.0N 86.5W 40 KT...EXTRATROPICAL 120HR VT 12/0600Z 27.0N 85.0W 35 KT...EXTRATROPICAL $$ FORECASTER BRENNAN |
