WDPN32 PGTW 020900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W 
(ATSANI) WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 23W (ATSANI), LOCATED APPROXIMATELY 504 
NM NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD 
AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) SHOWS A WEAK SYSTEM THAT HAS MAINTAINED AN OVERALL 
POORLY-ORGANIZED CONVECTIVE STRUCTURE DISPLACED WESTWARD FROM A WEAK 
AND RAGGED LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS 
PLACED WITH FAIR CONFIDENCE BASED ON THE PARTLY EXPOSED LLC IN THE 
MSI LOOP AND IN MICROWAVE IMAGES INCLUDING THE 020510Z AMSR2 AND THE 
020436Z ATMS IMAGES. THE INITIAL INTENSITY OF 25KTS IS BASED ON THE 
WIND FIELD AROUND THE LLC IN THE 012345Z DIRECT ASCAT PASS AND 
REFLECTS THE SUSTAINED 6-HR CONVECTIVE STRUCTURE. THE ENVIRONMENT IS 
MARGINAL WITH MODERATE (20-25KT) VERTICAL WIND SHEAR (VWS) AND WEAK 
OUTFLOW ALOFT OFFSET SLIGHTLY BY WARM (29-30C) SEA SURFACE 
TEMPERATURES (SST) IN THE PHILIPPINE SEA. THE CYCLONE IS TRACKING 
ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE 
(STR) TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TD 23W WILL TRACK MORE POLEWARD, AS IT ROUNDS THE WESTERN EDGE 
OF THE STR, INTO A COL AREA SOUTH OF A SHORTWAVE MIDLATITUDE TROUGH 
AND BETWEEN THE STEERING STR AND A SECONDARY STR TO THE NORTHWEST, 
WHERE IT WILL REMAIN IN A QUASI-STATIONARY (QS) STATE UP TO TAU 48. 
AFTERWARD, THE PRIMARY STR WILL BUILD AND SLOWLY DRIVE TD 23W WEST-
SOUTHWESTWARD AND OUT OF THE COL. THE ENVIRONMENT IS FORECAST TO 
IMPROVE AS VWS WEAKENS AND POLEWARD OUTFLOW INCREASES, FUELING A 
STEADY INTENSIFICATION TO 65KTS BY TAU 72. NUMERICAL MODELS DIVERGE 
SIGNIFICANTLY WITH VARYING SOLUTIONS IN THE DURATION OF QS STATE IN 
THE COL, LENDING LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST 
TRACK. 
   C. IN THE EXTENDED TAUS, THE PRIMARY STR WILL CONTINUE TO STEER TD 
23W WEST-SOUTHWESTWARD IN THE PHILIPPINE SEA, THROUGH LUZON STRAIT, 
AND INTO THE SOUTH CHINA SEA BY TAU 120. THE FAVORABLE ENVIRONMENT  
CONDITIONS WILL PROMOTE FURTHER INTENSIFICATION TO A PEAK OF 75KTS BY 
TAU 96. AFTERWARD, INCREASING VWS WILL WEAKEN THE SYSTEM TO 60KTS BY 
TAU 120. NUMERICAL MODELS SIGNIFICANTLY DIVERGE TO OVER 800 NM BY TAU 
120 WITH NAVGEM AND UEMN SUGGESTING A RECURVATURE INTO JAPAN, LENDING 
LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST.// 
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