[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 250300
TCDAT3
TROPICAL STORM DELTA DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
10 PM EST THU NOV 24 2005

DELTA HAS A BAND OF FAIRLY DEEP CONVECTION WITH TOPS COLDER THAN
-60C IN THE NORTHEASTERN QUADRANT... BUT THE OVERALL ORGANIZATION
OF THE INNER CORE DOES NOT APPEAR TO HAVE CHANGED APPRECIABLY
DURING THE PAST FEW HOURS. DVORAK INTENSITY ESTIMATES REMAIN 55
KT... WHILE CIRA AND CIMSS ESTIMATES BASED ON AN AMSU OVERPASS AT
2023Z WERE 60 AND 73 KT RESPECTIVELY. A QUIKSCAT OVERPASS AT ABOUT
21Z PROVIDED SEEMINGLY UNCONTAMINATED WIND SPEED ESTIMATES OF 55 KT
JUST OUTSIDE OF THE DEEP CONVECTION... AND THE WINDS ARE LIKELY A
LITTLE STRONGER BENEATH THE CONVECTION. THE ADVISORY INTENSITY IS
KEPT AT 60 KT USING A BLEND OF THE VARIOUS INTENSITY ESTIMATES. THE
QUIKSCAT DATA ALSO REVEAL THAT THE WIND FIELD IS NOT QUITE AS LARGE
AS IT WAS PREVIOUSLY... SO THE INITIAL AND FORECAST 34 KT RADII
HAVE BEEN DECREASED SOMEWHAT.

DELTA HAS BEEN MOVING SLOWLY SOUTHWARD DURING THE PAST SEVERAL HOURS
AT ABOUT 5 KT... APPARENTLY INFLUENCED BY THE DEEP-LAYER RIDGE TO
ITS WEST.  THE DYNAMICAL MODELS... INCLUDING THE GFS AND NOGAPS
THAT HAVE INITIALIZED THE POSITION AND MOTION REASONABLY WELL...
FORECAST THE RIDGE TO BREAK DOWN ON FRIDAY AND CORRESPONDINGLY FOR
DELTA TO EXPERIENCE LITTLE NET MOTION DURING THE NEXT 24 HOURS.
WITH A NEW MID- TO UPPER-LEVEL TROUGH FORECAST TO REPLACE THE RIDGE
WITHIN A COUPLE OF DAYS... DELTA SHOULD THEN MOVE TO THE NORTH AND
EVENTUALLY NORTHEAST AS ANTICIPATED BY ALL OF THE TRACK GUIDANCE.
THE NEW OFFICIAL TRACK FORECAST FOLLOWS THIS GENERAL SCENARIO...
WHICH IS AN EASTWARD SHIFT COMPARED TO THE PREVIOUS ADVISORY.  A
POTENTIAL COMPLICATING FACTOR... HOWEVER... IS A SEPARATE SURFACE
LOW PRESSURE SYSTEM FORECAST TO DEVELOP WEST OF DELTA IN
ASSOCIATION WITH THE NEW MID- TO UPPER-LEVEL TROUGH.  THE MODELS
GENERALLY AGREE THAT DELTA WILL REMAIN SEPARATED FAR ENOUGH EAST
FROM THAT SYSTEM AND NOT BE DRAWN WESTWARD LATE IN THE FORECAST
PERIOD... BUT THE EVOLUTION OF THE TWO SYSTEMS IN THE MODELS IS
QUITE COMPLEX AND COULD CHANGE.

EVEN THOUGH THE OFFICIAL INTENSITY FORECAST AND THE SHIPS GUIDANCE
DO NOT ANTICIPATE DELTA BECOMING A HURRICANE... IT COULD STILL DO
SO FOR A BRIEF PERIOD DURING THE NEXT 24-36 HOURS WHILE REMAINING
SO CLOSE TO THAT INTENSITY.  WESTERLY VERTICAL SHEAR SHOULD BEGIN
TO INCREASE IN ABOUT 36 HOURS... WHICH SHOULD INDUCE A GRADUAL
WEAKENING TREND.  THEREAFTER DELTA WILL MOVE NORTHWARD OVER
PROGRESSIVELY COOLER WATERS AND EVENTUALLY BECOME EXTRATROPICAL.


FORECASTER KNABB


FORECAST POSITIONS AND MAX WINDS

INITIAL      25/0300Z 23.7N  39.0W    60 KT
 12HR VT     25/1200Z 23.4N  39.0W    60 KT
 24HR VT     26/0000Z 23.7N  39.0W    60 KT
 36HR VT     26/1200Z 24.5N  38.8W    60 KT
 48HR VT     27/0000Z 26.1N  38.5W    55 KT
 72HR VT     28/0000Z 29.0N  38.0W    50 KT...BECOMING EXTRATROPICAL
 96HR VT     29/0000Z 31.5N  37.0W    50 KT...EXTRATROPICAL
120HR VT     30/0000Z 34.0N  34.5W    50 KT...EXTRATROPICAL


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