Tropical Discussion

By: NWS
By: NWS

TROPICAL STORM IDA
DISCUSSION NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1000 PM EST WED NOV 04 2009.
SINCE THE LAST AIRCRAFT PENETRATION OF THE STORM...THE CLOUD PATTERN OF IDA HAS REMAINED WELL ORGANIZED WITH A PROMINENT COLD-TOPPED CDO AND SOME BANDING FEATURES OVER THE NORTHERN SEMICIRCLE. A RECENT SSMIS OVERPASS REVEALED A BANDING-TYPE EYE IN MICROWAVE IMAGERY. DVORAK INTENSITY ESTIMATES WERE 45 KT FROM TAFB AND SAB BUT THESE ARE CONSTRAINED BY THE RULES OF THE TECHNIQUE. BASED ON THE EARLIER AIRCRAFT DATA AND CURRENT ORGANIZATION OF THE SYSTEM...THE CURRENT INTENSITY IS ESTIMATED TO BE 55 KT. THE UPPER-LEVEL OUTFLOW IS WELL DEFINED AND THERE REMAINS A SHORT PERIOD PRIOR TO LANDFALL FOR IDA TO STRENGTHEN A LITTLE MORE. RAPID WEAKENING IS LIKELY WHEN THE CYCLONE INTERACTS WITH THE MOUNTAINOUS TERRAIN OF CENTRAL AMERICA. IDA IS PROJECTED TO MOVE BACK OVER THE WATERS OF THE CARIBBEAN SEA IN ABOUT 3 DAYS. THE INTENSITY FORECAST IN THE LATTER PART OF THE PERIOD IS HIGHLY UNCERTAIN...HOWEVER...BECAUSE IT IS NOT CLEAR WHETHER THE TROPICAL CYCLONE WILL SURVIVE ITS TRANSIT OVER LAND. THE ESTIMATED INITIAL MOTION IS NOW NORTHWESTWARD OR 315/6. IDA IS BEING STEERED BY THE FLOW BETWEEN A WEAK RIDGE OVER THE NORTH-CENTRAL CARIBBEAN SEA AND A WEAK TROUGH OVER THE SOUTHWESTERN GULF OF MEXICO. AS THE RIDGE BUILDS NORTHWARD OVER THE NEXT FEW DAYS...THE TROPICAL CYCLONE SHOULD GRADUALLY TURN TOWARD THE NORTH-NORTHWEST. MOST OF THE TRACK MODELS ARE IN FAIR AGREEMENT ON A GENERAL NORTHWARD OR NORTH-NORTHWESTWARD MOTION...BUT VARY SIGNIFICANTLY IN FORWARD SPEED. THE OFFICIAL FORECAST IS A BLEND OF THE MODEL CONSENSUS AND THE PREVIOUS NHC TRACK. THE BIGGEST IMPACT OF THIS SLOW-MOVING SYSTEM WILL LIKELY BE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES CAUSED BY EXTREMELY HEAVY RAINS.


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