Tropical Storm IDA Forecast Discussion

000
WTNT41 KNHC 072056
TCDAT1
TROPICAL STORM IDA DISCUSSION NUMBER  14
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112009
400 PM EST SAT NOV 07 2009

THE SATELLITE APPEARANCE OF IDA HAS NOT CHANGED SIGNIFICANTLY THIS
AFTERNOON.  THE AIRCRAFT FOUND THE CENTER A LITTLE NORTH OF THE
EARLIER ESTIMATES...WELL EMBEDDED WITHIN THE CENTRAL DENSE
OVERCAST.  THE PLANE MEASURED A PEAK 850 MB FLIGHT-LEVEL WIND OF 68
KT AND A SFMR SURFACE WIND OF 60 KT. THESE DATA SUPPORT AN INITIAL
INTENSITY OF 60 KT.  CIRRUS ELEMENTS ARE MOVING NORTHEASTWARD...
SUGGESTING MODERATE SOUTHWESTERLY UPPER-LEVEL FLOW OVER THE
CYCLONE.  HOWEVER IT DOES NOT APPEAR THAT SHEAR WILL BE STRONG
ENOUGH IN THE SHORT-TERM TO INHIBIT SOME ADDITIONAL
INTENSIFICATION.  IDA WILL BE TRAVERSING THE VERY WARM WATER OF THE
NORTHWESTERN CARIBBEAN SEA AND THE INTENSITY GUIDANCE NOW
UNANIMOUSLY PREDICTS IDA TO BECOME A HURRICANE WITHIN 12
HOURS...AND THE OFFICIAL FORECAST FOLLOWS SUIT.  AFTER IDA REACHES
THE GULF OF MEXICO...THE SHEAR IS FORECAST TO INCREASE AND WATERS
BEGIN TO COOL. THESE FACTORS SHOULD CONTRIBUTE TO MORE STEADY
WEAKENING.

IDA HAS BEEN MOVING NORTHWARD AT A SLIGHTLY FASTER FORWARD SPEED
TODAY.  THE TRACK GUIDANCE IS TIGHTLY CLUSTERED ON A NORTH-
NORTHWESTWARD MOTION DURING THE NEXT 24 TO 36 HOURS.  THE OFFICIAL
FORECAST DURING THIS PERIOD REMAINS NEAR THE MODEL CONSENSUS BUT HAS
BEEN ADJUSTED A LITTLE EASTWARD PRIMARILY DUE TO THE MORE NORTHWARD
INITIAL POSITION AND HEADING.  THEREAFTER...THERE REMAINS
SIGNIFICANT DIFFERENCES IN THE GUIDANCE AS TO HOW IDA INTERACTS
WITH A MID- TO UPPER-LEVEL TROUGH THAT MOVES INTO THE NORTHWESTERN
GULF OF MEXICO IN A COUPLE OF DAYS.  THE 12Z GFS...ECMWF...AND HWRF
CONTINUE TO SHOW THE CYCLONE REACHING THE NORTHERN GULF COAST IN
ABOUT 72 HOURS AS IT BECOMES AN EXTRATROPICAL CYCLONE.  THE
OFFICIAL FORECAST IS A LITTLE FASTER THAN THE PREVIOUS ONE...AND
HAS ONCE AGAIN BEEN SHIFTED NORTHWARD.  THE NEW TRACK NOW SHOWS A
POSITION JUST SOUTH OF THE NORTHERN GULF COAST IN 3 DAYS.
THEREAFTER...MOST OF THE GUIDANCE TURNS THE CYCLONE EASTWARD...AND
SO DOES THE OFFICIAL FORECAST.  BY 120 HOURS...SOME OF THE GUIDANCE
SUGGEST THAT THE LOW WILL BE ABSORBED BY A FRONTAL BOUNDARY...AND
THE OFFICIAL FORECAST DOES NOT PROVIDE A 5-DAY POSITION FOR THIS
REASON.

MOST OF THE GLOBAL MODELS SHOW A LARGE PRESSURE GRADIENT BETWEEN
A HIGH PRESSURE RIDGE OVER THE SOUTHEASTERN UNITED STATES AND THE
TROPICAL CYCLONE.  THIS IS ALREADY CONTRIBUTING TO A LARGE AREA OF
STRONG WINDS OVER THE SOUTHERN GULF OF MEXICO WHICH IS NOT DIRECTLY
ATTRIBUTABLE TO IDA.

FORECAST POSITIONS AND MAX WINDS

INITIAL      07/2100Z 18.9N  84.3W    60 KT
 12HR VT     08/0600Z 20.1N  84.8W    75 KT
 24HR VT     08/1800Z 21.6N  85.8W    70 KT
 36HR VT     09/0600Z 23.8N  87.2W    60 KT
 48HR VT     09/1800Z 26.3N  88.0W    50 KT
 72HR VT     10/1800Z 29.5N  87.3W    45 KT...EXTRATROPICAL
 96HR VT     11/1800Z 29.5N  86.0W    40 KT...EXTRATROPICAL
120HR VT     12/1800Z...DISSIPATED

$$
FORECASTER BROWN