[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT41 KNHC 090301
TCDAT1
HURRICANE IDA DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112009
900 PM CST SUN NOV 08 2009

THE SATELLITE APPEARANCE OF IDA HAS CHANGED VERY LITTLE SINCE THE
AIRCRAFT DEPARTED THE HURRICANE JUST BEFORE 0000 UTC.  DURING THE
LAST COUPLE OF PASSES THROUGH THE CENTER THE AIRCRAFT MEASURED A
MAXIMUM 700 MB FLIGHT-LEVEL WIND OF 108 KT AND A SFMR SURFACE WIND
OF 84 KT. THESE DATA SUPPORT AN INTENSITY OF 90 KT.  ANOTHER AIR
FORCE PLANE IS SCHEDULED TO REACH IDA AROUND 0600 UTC.

THE LAST FEW AIRCRAFT FIXES PROVIDE A FAIRLY CONFIDENT INITIAL
MOTION OF 345/12...A LITTLE FASTER THAN BEFORE.  IDA IS FORECAST TO
CONTINUE MOVING NORTHWARD BETWEEN A MID/UPPER-LEVEL TROUGH OVER THE
WESTERN GULF MEXICO AND A MID/UPPER-LEVEL RIDGE OVER THE EASTERN
GULF OF MEXICO AND THE NORTHERN CARIBBEAN SEA.  THE TRACK MODELS
APPEAR TO BE IN A LITTLE BETTER AGREEMENT ON A NORTH-NORTHWESTWARD
TO NORTHWARD TRACK DURING THE NEXT 24-36 HOURS.  THE 12Z RUNS OF
THE ECMWF AND UKMET ARE A LITTLE WEST OF THE REMAINDER OF THE
GUIDANCE AND SHOW A TRACK NEAR EXTREME SOUTHEASTERN LOUISIANA.
DURING THE FIRST 24-36 HOURS...THE NEW OFFICIAL FORECAST IS NEAR
THE MODEL CONSENSUS AND THE PREVIOUS TRACK...BUT IS A LITTLE
FASTER.  AFTER LANDFALL ALONG THE NORTHERN GULF COAST...THE MODELS
TURN IDA EASTWARD THEN SOUTHEASTWARD AND THE NHC FORECAST FOLLOWS
SUIT...BUT DOES NOT SHOW AS SHARP A SOUTHEASTWARD TURN AS SOME OF
THE GUIDANCE INDICATES.  THE AIR FORCE ALSO FLEW A SURVEILLANCE
MISSION AROUND AND NORTH OF THE HURRICANE THIS AFTERNOON AND THAT
DATA SHOULD BE ASSIMILATED INTO THE 0000 UTC MODELS.

IDA IS FORECAST TO TRAVERSE COOLER WATERS...AND MOVE INTO A
COOLER AIRMASS AND INCREASING SHEAR DURING THE NEXT 24-36 HOURS.
AS THE CYCLONE APPROACHES THE NORTHERN GULF COAST IT WILL ALSO
LIKELY BEGIN EXTRATROPICAL TRANSITION.  HOWEVER...IT IS BECOMING
MORE LIKELY THAT IDA WILL RETAIN ITS TROPICAL CHARACTERISTICS
THROUGH LANDFALL.  THE INTENSITY GUIDANCE FORECASTS GRADUAL
WEAKENING AND ALL SHOW IDA AROUND HURRICANE STRENGTH AT LANDFALL.
THE OFFICIAL FORECAST IS IN LINE WITH THE GUIDANCE AND KEEPS THE
CYCLONE A HURRICANE WHEN IT REACHES THE COAST.  THIS HAS REQUIRED
THE ISSUANCE OF A HURRICANE WARNING FOR A PORTION OF THE NORTHERN
GULF COAST.

FORECAST POSITIONS AND MAX WINDS

INITIAL      09/0300Z 23.7N  86.7W    90 KT
 12HR VT     09/1200Z 25.8N  87.5W    85 KT
 24HR VT     10/0000Z 28.5N  87.7W    75 KT
 36HR VT     10/1200Z 30.5N  87.1W    65 KT...INLAND
 48HR VT     11/0000Z 31.2N  85.8W    40 KT...EXTRATROPICAL
 72HR VT     12/0000Z 30.5N  82.0W    30 KT...EXTRATROPICAL
 96HR VT     13/0000Z...DISSIPATED

$$
FORECASTER BROWN



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