Tropical Storm IDA Forecast Discussion

000
WTNT41 KNHC 080246
TCDAT1
TROPICAL STORM IDA DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112009
1000 PM EST SAT NOV 07 2009

THERE HAS BEEN LITTLE CHANGE TO THE SATELLITE APPEARANCE OF IDA
SINCE THE AIR FORCE PLANE LEFT EARLIER THIS AFTERNOON.  THE
LOW-LEVEL CENTER IS STILL EMBEDDED WITHIN A LARGE CENTRAL DENSE
OVERCAST ALTHOUGH RECENT MICROWAVE DATA SUGGEST THAT THE SYSTEM IS
BEING IMPACTED BY SOME SOUTHERLY SHEAR.  THE INTENSITY WILL BE HELD
AT 60 KT FOR THIS ADVISORY...WHICH IS SUPPORTED BY DVORAK ESTIMATES
OF 55 KT FROM BOTH TAFB AND SAB AND AN OBJECTIVE ADT ESTIMATE OF 61
KT.  ANOTHER AIR FORCE RECONNAISSANCE AIRCRAFT IS SCHEDULED TO
INVESTIGATE IDA IN A FEW HOURS TO PROVIDE UPDATED INFORMATION.

IDA HAS TURNED TO THE NORTH-NORTHWEST WITH AN INITIAL MOTION OF 340
DEGREES AT 10 KT AS IT IS STEERED BETWEEN AN AMPLIFIED TROUGH OVER
MEXICO AND A MID-LEVEL RIDGE THAT EXTENDS FROM THE SOUTHEASTERN
U.S. TO HISPANIOLA.  THE TRACK GUIDANCE IS IN EXCELLENT AGREEMENT
THROUGH 48 HOURS ON A CONTINUED NORTH-NORTHWESTWARD MOTION...AND
THE NEW OFFICIAL FORECAST IS ONLY SLIGHTLY TO THE EAST OF THE
PREVIOUS FORECAST.  THEREAFTER...ALL THE MODELS BRING IDA TO THE
COAST NEAR THE FLORIDA PANHANDLE AS AN EXTRATROPICAL CYCLONE BUT
QUICKLY TURN IT TO THE SOUTHEAST AS THE ABSORBING COLD FRONT
PUSHES SOUTHWARD OVER THE GULF.

ALTHOUGH SOME SHEAR IS AFFECTING IDA...IT IS NOT PROHIBITIVELY
STRONG.  STRONG UPPER-LEVEL WINDS NORTH OF THE SYSTEM ARE PROVIDING
SOME DIFFLUENCE ALOFT...AND THIS WILL CONTINUE TO GIVE IDA A 24-36
HOUR WINDOW TO STRENGTHEN TO A HURRICANE.  THE SHEAR IS EXPECTED TO
INCREASE AFTER 36 HOURS AND SHOULD LEAD TO SOME WEAKENING...BUT THE
NEW INTENSITY GUIDANCE INDICATES THAT THIS WEAKENING COULD BE
SLOWER TO OCCUR THAN PREVIOUSLY FORECAST.  IDA SHOULD BEGIN THE
EXTRATROPICAL TRANSITION PROCESS AROUND 48 HOURS AND BE FULLY
EXTRATROPICAL BY 72 HOURS.

A TIGHT PRESSURE GRADIENT BETWEEN IDA AND HIGH PRESSURE LOCATED OVER
THE SOUTHEASTERN UNITED STATES IS ALREADY PRODUCING STRONG WINDS
OVER THE SOUTHEASTERN GULF OF MEXICO...BUT THESE WINDS ARE NOT
DIRECTLY ATTRIBUTABLE TO THE CIRCULATION OF IDA. 

FORECAST POSITIONS AND MAX WINDS

INITIAL      08/0300Z 20.1N  84.6W    60 KT
 12HR VT     08/1200Z 21.2N  85.3W    70 KT
 24HR VT     09/0000Z 23.0N  86.5W    70 KT
 36HR VT     09/1200Z 25.4N  87.6W    65 KT
 48HR VT     10/0000Z 27.7N  87.9W    60 KT
 72HR VT     11/0000Z 30.0N  86.5W    45 KT...EXTRATROPICAL
 96HR VT     12/0000Z 29.0N  85.5W    35 KT...EXTRATROPICAL
120HR VT     13/0000Z...ABSORBED BY FRONT

$$
FORECASTER BERG/FRANKLIN