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WTNT41 KNHC 081516
TCDAT1
HURRICANE IDA DISCUSSION NUMBER 18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112009
900 AM CST SUN NOV 08 2009
THE LAST PASS OF AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT NEAR
1100 UTC SHOWED A CENTRAL PRESSURE OF 983 MB AND AN ELLIPTICAL EYE.
SATELLITE IMAGERY AND RADAR DATA FROM CUBA AND MEXICO SINCE THAT
TIME SUGGEST LITTLE CHANGE HAS OCCURRED IN THE STRUCTURE. BASED ON
THIS AND SATELLITE INTENSITY ESTIMATES OF 90 AND 77 KT FROM TAFB
AND SAB...THE INITIAL INTENSITY REMAINS 80 KT. ANALYSES FROM CIMSS
AT THE UNIVERSITY OF WISCONSIN INDICATE THAT THE HURRICANE IS
CURRENTLY EXPERIENCING ABOUT 20 KT OF SOUTHWESTERLY VERTICAL WIND
SHEAR.
THE INITIAL MOTION IS 325/9. IDA REMAINS BETWEEN A MID/UPPER-LEVEL
TROUGH OVER THE WESTERN GULF MEXICO AND ADJACENT LAND AREAS AND AN
MID/UPPER-LEVEL RIDGE OVER THE EASTERN GULF OF MEXICO AND THE
NORTHERN CARIBBEAN SEA. IN ADDITION...A STRONG LOW-LEVEL RIDGE
COVERS THE NORTHERN GULF OF MEXICO. THE DYNAMICAL MODELS FORECAST
THE TROUGH AND RIDGE TO MOVE EASTWARD...ALLOWING IDA TO TURN TOWARD
THE NORTH DURING THE NEXT 36 HR OR SO. THE GFDL...HWRF...GFS...
ECMWF...AND CANADIAN MODELS ARE NOW FORECASTING A FASTER NORTHWARD
MOTION...WITH THE CENTER OF IDA REACHING THE NORTHERN GULF COAST IN
36-48 HR. THE UKMET AND NOGAPS MODELS CONTINUE TO SHOW A SLOWER
FORWARD SPEED. THE NEW FORECAST TRACK IS FASTER THAN THE PREVIOUS
TRACK THROUGH 48 HR...ALTHOUGH IT IS SLOWER THAN THE GFDL AND ITS
COLLEAGUES. THE FASTER NORTHWARD MOTION ALSO RESULTS IN A MORE
NORTHERLY POSITION FOR THE LATER PART OF THE FORECAST TRACK...SO
THE 72-96 HR POSITIONS HAVE BEEN ADJUSTED NORTHWARD AS WELL.
SOME STRENGTHENING IS POSSIBLE TODAY. AFTER THAT...IDA WILL BE
MOVING OVER COOLER SEA SURFACE TEMPERATURES...INTO A COOLER AIR
MASS...AND INTO STRONGER SHEAR. THE DYNAMICAL MODELS AGREE THAT
EXTRATROPICAL TRANSITION SHOULD BEGIN BY ABOUT 24 HOURS AND IS
LIKELY TO BE COMPLETE IN ABOUT 48 HR. HOWEVER...THE INTENSITY
GUIDANCE FORECASTS HURRICANE-FORCE WINDS THROUGH 48 HR...SO THE
INTENSITY FORECAST MAINTAINS HURRICANE STRENGTH THROUGH THAT TIME.
IN THE 72-120 HR TIME FRAME...THE GFS...ECMWF...AND CANADIAN MODELS
FORECAST A LARGE BAROCLINIC LOW OFF THE U. S. EAST COAST. IT IS
NOT CLEAR WHETHER THIS IS THE REMAINS OF IDA OR A SECOND LOW THAT
ABSORBS IDA. AT THIS TIME...THE FORECAST USES THE SCENARIO THAT
THIS IS A SECOND LOW THAT ABSORBS THE REMAINS OF IDA.
WHILE IT IS LIKELY THAT IDA WILL LOSE TROPICAL CYCLONE
CHARACTERISTICS BEFORE REACHING THE NORTHERN GULF COAST...IT IS
POSSIBLE THAT TROPICAL STORM- OR HURRICANE-FORCE WINDS COULD REACH
PORTIONS OF THE COAST BEFORE EXTRATROPICAL TRANSITION IS COMPLETE.
THUS...A HURRICANE WATCH HAS BEEN ISSUED FOR PORTIONS OF THE
NORTHERN GULF COAST AT THIS TIME. OTHER POTENTIAL HAZARDS
ASSOCIATED WITH IDA ARE...FOR NOW...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 08/1500Z 21.2N 86.0W 80 KT
12HR VT 09/0000Z 22.8N 87.1W 85 KT
24HR VT 09/1200Z 25.6N 88.4W 85 KT
36HR VT 10/0000Z 28.2N 88.6W 75 KT
48HR VT 10/1200Z 30.0N 87.8W 65 KT...EXTRATROPICAL
72HR VT 11/1200Z 30.5N 84.5W 40 KT...EXTRATROPICAL INLAND
96HR VT 12/1200Z 30.0N 81.0W 30 KT...EXTRATROPICAL
120HR VT 13/1200Z...ABSORBED BY EXTRATROPICAL LOW
FORECASTER BEVEN
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