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WTNT41 KNHC 060241
TCDAT1
TROPICAL DEPRESSION IDA DISCUSSION NUMBER 7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112009
1000 PM EST THU NOV 05 2009
SURFACE OBSERVATIONS AND CONVENTIONAL SATELLITE IMAGERY INDICATE
THAT IDA HAS WEAKENED TO A TROPICAL DEPRESSION. WHAT REMAINS OF THE
DIMINISHING DEEP CONVECTION IS CURRENTLY CONFINED TO NORTHWEST AND
NORTHEAST QUADRANTS. SOME FURTHER WEAKENING IS LIKELY DURING THE
NEXT 12 TO 24 HOURS AS IDA CONTINUES ON A GENERAL NORTHWARD TRACK
OVER NORTHEASTERN NICARAGUA AND EASTERN HONDURAS. AROUND THE 36
HOUR PERIOD...THE CYCLONE SHOULD EMERGE OVER THE NORTHWEST
CARIBBEAN SEA AND...ASSUMING THE CIRCULATION IS NOT TOO SEVERELY
DISRUPTED BY ITS PASSAGE OVER LAND...THE SYSTEM SHOULD RESTRENGTHEN
INTO A TROPICAL STORM. HOWEVER...THE GLOBAL MODELS INDICATE ONLY A
MARGINALLY FAVORABLE UPPER-LEVEL WIND ENVIRONMENT OVER THE
REGION...WHICH SHOULD CURTAIL SIGNIFICANT INTENSIFICATION AS IDA
HEADS IN THE GENERAL DIRECTION OF THE YUCATAN CHANNEL. AFTER IDA
ENTERS THE SOUTHERN GULF OF MEXICO....THE INTENSITY FORECAST IS
HIGHLY UNCERTAIN. THE LARGE-SCALE MODELS ALL AGREE ON AN
INCREASINGLY STRONG VERTICAL SHEAR ENVIRONMENT DEVELOPING OVER THE
GULF OF MEXICO TOWARD THE END OF THE FORECAST PERIOD. THE GFDL AND
HWRF MODELS...PARTICULARLY THE FORMER...SHOW SIGNIFICANT
INTENSIFICATION OF IDA IN THE LATTER PART OF THE PERIOD. IT SHOULD
BE RECALLED HOWEVER THAT THESE MODELS HAVE BEEN KNOWN TO HAVE A
HIGH BIAS IN STRONGLY SHEARED ENVIRONMENTS...AS WAS THE CASE WITH
TROPICAL STORMS DANNY...ERIKA...AND HENRI OF THIS YEAR.
CONSEQUENTLY...THE OFFICIAL WIND SPEED FORECAST LEANS MORE TOWARD
THE WEAKER LGEM AND SHIPS PREDICTIONS.
THE INITIAL MOTION IS ESTIMATED TO BE 330/4...WITHIN THE SOUTHERLY
STEERING FLOW ON THE WEST SIDE OF A WEAK MID-LEVEL RIDGE. WITH THE
EXCEPTION OF FORWARD SPEED DISPARITIES...THE GLOBAL AND REGIONAL
MODELS CONTINUE TO INDICATE A GENERAL NORTH TO NORTH-NORTHWESTWARD
MOTION INTO THE CENTRAL GULF OF MEXICO OVER THE NEXT 4 DAYS.
AROUND THE END OF THE PERIOD...MOST OF THE TRACK GUIDANCE SHOWS A
TURN TO THE RIGHT AS IDA BEGINS TO INTERACT WITH THE WESTERLIES.
THE OFFICIAL FORECAST HAS CHANGED LITTLE FROM THE PREVIOUS ONE AND
IS CLOSE TO THE MODEL CONSENSUS.
THE BIGGEST IMPACT OF THIS SLOW-MOVING SYSTEM DURING THE NEXT DAY OR
SO WILL LIKELY BE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES
CAUSED BY EXTREMELY HEAVY RAIN OVER PORTIONS OF NICARAGUA AND
HONDURAS.
FORECAST POSITIONS AND MAX WINDS
INITIAL 06/0300Z 13.8N 84.1W 30 KT
12HR VT 06/1200Z 14.4N 84.1W 25 KT...INLAND
24HR VT 07/0000Z 15.4N 84.2W 25 KT...INLAND
36HR VT 07/1200Z 16.6N 84.5W 35 KT...OVER WATER
48HR VT 08/0000Z 17.7N 85.0W 40 KT
72HR VT 09/0000Z 20.3N 86.2W 45 KT
96HR VT 10/0000Z 23.0N 87.5W 45 KT
120HR VT 11/0000Z 26.0N 87.0W 45 KT
FORECASTER PASCH/ROBERTS
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