[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 080900
TCDAT1
HURRICANE IDA DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112009
300 AM CST SUN NOV 08 2009

DATA FROM THE AIR FORCE HURRICANE HUNTER AIRCRAFT SUGGEST THAT THE
INTENSIFICATION OF IDA HAS HALTED...AT LEAST TEMPORARILY. THE
LATEST PRESSURE MEASURED ON A PASS THROUGH THE CENTER WAS 984
MB...AND THE INITIAL INTENSITY IS HELD AT 80 KT FOR THIS ADVISORY.
THE INTENSITY FORECAST SHOWS SOME STRENGTHENING IN THE SHORT
TERM...AS IDA WILL REMAIN OVER VERY WARM WATERS THROUGH THE NEXT 24
HOURS. BEYOND THAT TIME...IDA WILL BEGIN TO MOVE OVER MUCH COOLER
WATERS...BELOW 26C AFTER 48 HOURS...AND VERTICAL SHEAR WILL
INCREASE MARKEDLY AS STRONG UPPER-LEVEL SOUTHWESTERLY FLOW AHEAD OF
A MID- TO UPPER-LEVEL TROUGH IMPINGES ON IDA. GLOBAL MODEL GUIDANCE
SHOWS IDA UNDERGOING EXTRATROPICAL TRANSITION IN THE 48 TO 72 HOUR
TIME FRAME AS IT INTERACTS WITH THE TROUGH AND A SURFACE FRONT
ALONG THE NORTHERN GULF COAST. THE OFFICIAL FORECAST SHOWS GRADUAL
WEAKENING FROM 24 TO 48 HOURS...AND MORE RAPID WEAKENING AS IDA
BECOMES EXTRATROPICAL.

THE INITIAL MOTION ESTIMATE IS NORTHWEST...OR 325/10. THIS IS TO THE
LEFT OF THE PREVIOUS PACKAGE...AS THE FLOW AROUND A MID- TO
UPPER-LEVEL TROUGH OVER SOUTHERN MEXICO AND GUATEMALA MAY BE
TUGGING IDA A LITTLE MORE TOWARD THE WEST. THE TRACK GUIDANCE IS IN
GOOD AGREEMENT ON A TURN TOWARD THE NORTH-NORTHWEST AND THE NORTH
OVER THE NEXT 48 HOURS AS IDA ACCELERATES AHEAD OF THE TROUGH THAT
MOVES INTO THE NORTHERN GULF. GIVEN THE MORE WESTERLY COMPONENT OF
THE INITIAL MOTION...THE TRACK GUIDANCE HAS SHIFTED WESTWARD
COMPARED TO THE LAST PACKAGE...AND SO HAS THE OFFICIAL FORECAST...
WHICH NOW TAKES THE CENTER OF IDA VERY CLOSE TO THE NORTHEASTERN TIP
OF THE YUCATAN PENINSULA TODAY. IDA WILL THEN MOVE INTO THE GULF OF
MEXICO AND APPROACH THE EAST-CENTRAL GULF COAST IN 48 TO 72 HOURS.
MOST OF THE TRACK GUIDANCE SHOWS A TURN TOWARD THE EAST AND
SOUTHEAST AT DAYS 3 AND 4 AS IDA BECOMES EXTRATROPICAL. HOWEVER...
THERE IS LARGE SPREAD IN THE GUIDANCE WITH REGARD TO THE ULTIMATE
FATE OF IDA. FOR EXAMPLE...THE ECMWF SHOWS THE EXTRATROPICAL
REMNANTS OF IDA CONTINUING ACROSS THE SOUTHEASTERN UNITED
STATES...WHILE THE GFS LEAVES THE REMNANTS OF IDA BEHIND A STRONGER
BAROCLINIC LOW THAT FORMS OVER THE SOUTHEASTERN UNITED STATES.
GIVEN THE LARGE RANGE OF POSSIBLE SOLUTIONS...THE OFFICIAL FORECAST
SHOWS A SLOW SOUTHEASTWARD MOTION AT DAY 4...AND HAS IDA
DISSIPATING AS IT IS ABSORBED INTO A FRONTAL ZONE BY DAY 5. THERE
IS A HIGH DEGREE OF UNCERTAINTY IN THIS PART OF THE FORECAST
SCENARIO.

THE OFFICIAL FORECAST SHOWS TROPICAL STORM FORCE WINDS REACHING
PORTIONS OF THE U.S. GULF COAST IN A COUPLE OF DAYS.  HOWEVER...
SINCE IDA IS EXPECTED TO BEGIN UNDERGOING EXTRATROPICAL TRANSITION
AROUND THAT TIME...THESE HAZARDS ARE 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      08/0900Z 20.5N  85.6W    80 KT
 12HR VT     08/1800Z 21.8N  86.7W    85 KT
 24HR VT     09/0600Z 24.0N  87.8W    85 KT
 36HR VT     09/1800Z 26.7N  88.5W    80 KT
 48HR VT     10/0600Z 28.5N  88.2W    65 KT
 72HR VT     11/0600Z 29.8N  86.1W    45 KT...EXTRATROPICAL
 96HR VT     12/0600Z 28.0N  84.0W    30 KT...EXTRATROPICAL
120HR VT     13/0600Z...DISSIPATED

$$
FORECASTER BRENNAN/KIMBERLAIN



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