Tropical Storm ATSANI Advisory Sat Nov 07

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (ATSANI) WARNING NR
036//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 23W (ATSANI), LOCATED APPROXIMATELY 191 NM
SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED WEST-NORTHWESTWARD AT 02
KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) REVEALS A FULLY-EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC) WITH TIGHTLY-CURVED BANDING WRAPPING INTO
THE CENTER. FURTHERMORE, THE MSI INDICATES THAT THE SYSTEM HAS
DEGRADED, SHOWING ONLY SHORT BURSTS OF DEEP CONVECTION OVER THE
NORTHEAST QUADRANT, RAPIDLY BEING SHEARED TO THE NORTHEAST UNDER
MODERATE (20-25 KT) VERTICAL WIND SHEAR (VWS). BASED ON THE FULLY-
EXPOSED LLCC IN MSI AND A WELL-DEFINED LLCC IN A 070530Z AMSR2 89
GHZ MICROWAVE IMAGE, THERE IS GOOD CONFIDENCE IN THE INITIAL
POSITION. THE INITIAL INTENSITY IS ASSESSED AT 40 KTS AND IS HEDGED
SLIGHTLY HIGHER THAN MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES
OF T2.5 (35 KTS, PGTW/RJTD) BASED ON A 070528Z AMSR2 WINDSPEED
ESTIMATE REVEALING AN AREA WITH 40 KT WINDS TO THE NORTH. IN
CONJUNCTION WITH THE AFOREMENTIONED MODERATE VWS, ENVIRONMENTAL
ANALYSIS REVEALS MARGINALLY WARM (25-26 CELSIUS) SEA SURFACE
TEMPERATURES (SST) AND ENHANCED POLEWARD OUTFLOW, CONTRIBUTING TO AN
OVERALL MARGINAL ENVIRONMENT. TS 23W IS SLOWLY TRACKING ALONG THE
SOUTHWESTERN PERIPHERY OF A WEAK SUBTROPICAL RIDGE (STR) POSITIONED
TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 23W IS EXPECTED TO TURN SHARPLY SOUTHWESTWARD AFTER TAU 06
AS LOW-LEVEL RIDGING ASSOCIATED WITH A NORTHEAST SURGE EVENT
STRENGTHENS OVER THE EAST CHINA SEA. TS 23W IS FORECAST TO
ACCELERATE ALONG THIS TRACK AS IT STEADILY WEAKENS DUE TO INCREASING
(30+ KTS) VWS AND COOLER SST VALUES (24-26 CELSIUS). THE SYSTEM IS
EXPECTED TO DISSIPATE OVER WATER BY TAU 36, IF NOT SOONER, AS THE
ENVIRONMENT QUICKLY DEGRADES. OVER THE PAST SIX HOURS, NUMERICAL
MODEL GUIDANCE HAS SIGNIFICANTLY CHANGED, WITH SEVERAL MODELS LOSING
THE VORTEX SIGNATURE WITHIN THE POOR ENVIRONMENT AND OTHER MODEL
SOLUTIONS LOSING THE VORTEX SIGNATURE IN THE NEXT 12 HOURS. HOWEVER,
THE JTWC TRACK HAS MAINTAINED A 36 HOUR FORECAST TO ACCOUNT FOR THE
TIME NEEDED FOR THE SYSTEM TO WEAKEN. BASED ON THE MODEL CHANGE AND
GENERALLY UNFAVORABLE ENVIRONMENT, THERE IS LOW CONFIDENCE IN THE
JTWC FORECAST TRACK.//
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