
WDPN32 PGTW 142100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 08W WARNING
NR 03//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION 08W (EIGHT), LOCATED APPROXIMATELY 172 NM
SOUTH-SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED EAST-NORTHEASTWARD
AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY SHOWS DIMINISHING DEEP CONVECTION AND
BANDING WRAPPING INTO A CLOUD-COVERED LOW LEVEL CIRCULATION CENTER.
THE INITIAL POSITION IS BASED ON INFLOW AND BANDING FEATURES IN THE
EIR LOOP, AND LIES TO THE NORTHWEST OF THE 18Z PGTW FIX AND SLIGHTLY
BEHIND THE 18Z RJTD FIX. THERE IS LOW CONFIDENCE IN THE INITIAL
POSITION. THE INITIAL INTENSITY OF 30 KNOTS IS BASED ON A 141259Z
ASCAT PASS REVEALING BROAD AREAS OF 25 AND 35 KT WIND BARBS AND AN
ELONGATED SURFACE CIRCULATION. THE INITIAL INTENSITY OF 30 KTS IS
HEDGED ABOVE RJTD AND PGTW CURRENT INTENSITY FIXES OF T1.5 (25 KTS).
THE BROADER AREA OF 25-30 KT WINDS, AS WELL AS DEEP CONVECTION
DEPICTED IN A 141756Z ATMS MICROWAVE IMAGE, IS TO THE SOUTH OF THE
CIRCULATION, AND RELATED TO THE CLIMATOLOGICAL SOUTHWESTERLY MONSOON
SURGE IN THE AREA. ENVIRONMENTAL ANALYSIS SHOWS THAT POLEWARD
OUTFLOW IS BEING ENHANCED BY THE MIDLATITUDE WESTERLY JET
IMMEDIATELY TO THE NORTH OF TD 08W. TD 08W IS EXPERIENCING FAVORABLE
VERTICAL WIND SHEAR (5 TO 10 KNOTS) AND WARM SEA SURFACE
TEMPERATURES (29-30 DEGREES C). HOWEVER, 08W IS LOCATED JUST
OFFSHORE OF TAIWAN, AND THE OTHERWISE FAVORABLE ENVIRONMENT IS BEING
COUNTERACTED BY LAND INTERACTION. A 141100Z AMSU TEMPERATURE ANOMALY
CROSS-SECTION SHOWS THAT TD 08W HAS MAINTAINED WEAK WARM CORE
CHARACTERISTICS. TD 08W IS TRACKING NORTHEASTWARD NEAR THE BAIU
FRONTAL BOUNDARY, AND HAS SLOWED ITS FORWARD MOTION NOTICEABLY IN
THE LAST 6 HOURS DUE TO LAND
INTERACTION WITH TAIWAN.
3. FORECAST REASONING.
A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TD 08W WILL CONTINUE TO TRACK NORTHEASTWARD ALONG THE BAIU
FRONTAL BOUNDARY THROUGHOUT THE FORECAST PERIOD. TD 08W WILL
MAINTAIN ITS 30 KT INTENSITY AS IT TRACKS OVER TAIWAN. BY TAU 24, TD
08W WILL BE NORTH OF TAIWAN, UNDER THE MIDLATITUDE JET, AND WILL
INTERACT WITH THE BAROCLINIC ZONE AND BEGIN EXTRATROPICAL
TRANSITION. TD 08W WILL CONTINUE EXTRATROPICAL TRANSITION THROUGH TAU
36 WHILE LIKELY MAINTAINING INTENSITY BUT INCREASING THE EXPANSE OF
ITS WIND FIELD. EXTRATROPICAL TRANSITION WILL BE COMPLETE BY TAU 48
AS 08W ACCELERATES TO THE NORTHEAST UNDER STRONG VERTICAL WIND SHEAR
AND ENCOUNTERS COOLER SEA SURFACE TEMPERATURES. THE JTWC FORECAST
TRACK IS HEDGED BEHIND AND SLIGHTLY SOUTH OF CONSENSUS, AS THE ECMF
MODEL TRACKER DEPICTS SLOWER FORWARD MOTION THAN THE OTHER TRACKERS,
AND MOVES 08W DUE EASTERLY AND SLOWLY ACROSS TAIWAN BEFORE CURVING
TO THE NORTHEAST. THERE IS FAIR CONFIDENCE IN THE JTWC FORECAST
TRACK.//
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