WDPN32 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (ATSANI) 
WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 23W (ATSANI), LOCATED APPROXIMATELY 689 NM 
EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 16 
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) SHOWS A WEAK SYSTEM THAT HAS MAINTAINED AN OVERALL 
POORLY-ORGANIZED CONVECTIVE STRUCTURE. THE INITIAL POSITION IS 
PLACED WITH LOW CONFIDENCE BASED ON LOW-CLOUD TRACING INTO AN 
OBSCURED LOW LEVEL CIRCULATION IN THE MSI LOOP. THE INITIAL 
INTENSITY OF 30 KTS IS BASED ON THE DVORAK ESTIMATE ESTIMATE OF 
T2.0/30KTS FROM PGTW. THE ENVIRONMENT IS OVERALL UNFAVORABLE WITH 
MODERATE (20-25KT) VERTICAL WIND SHEAR (VWS) AND WEAK OUTFLOW ALOFT 
OFFSET BY WARM (29-30C) SEA SURFACE TEMPERATURES (SST). 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 CONTINUE ON ITS CURRENT TRACK IN THE PHILIPPINE 
SEA UNDER THE AFOREMENTIONED STR. AFTER TAU 24, A SHORTWAVE 
MIDLATITUDE TROUGH APPROACHING FROM THE NORTHWESTWILL ERODE AND 
SPLIT THE STR AND PULL THE CYCLONE POLEWARD INTO A QUASI-STATIONARY 
STATE IN THE COL ZONE BETWEEN THE TWO RIDGES. THE ENVIRONMENT IS 
FORECAST TO IMPROVE SLIGHTLY AS VWS WEAKENS AND POLEWARD OUTFLOW 
IMPROVES, FUELING A STEADY INTENSIFICATION TO 60KTS BY TAU 72. 
NUMERICAL MODELS ARE IN GOOD AGREEMENT UP TO TAU 24 WITH NAVGEM THE 
SOLE OUTLIER TO THE RIGHT. AFTERWARD, THE 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 SECONDARY STR BEHIND THE SHORTWAVE 
TROUGH WILL ASSUME STEERING AND SLOWLY DRIVE TD 23W WESTWARD. 
ENVIRONMENTAL CONDITIONS ARE FORECAST TO IMPROVE EVEN MORE WITH 
DECREASED VWS (10-15KTS) AND THE ADDITION OF AN EQUATORWARD OUTFLOW 
CHANNEL. THESE CONDITIONS, COUPLED WITH CONTINUED WARM SST, WILL 
ALLOW FOR FURTHER INTENSIFICATION TO 85KTS AS IT CROSSES THE LUZON 
STRAIT. NUMERICAL MODELS SIGNIFICANTLY DIVERGE TO 400 NM BY TAU 120 
WITH VARYING TRACK SPEEDS, LENDING POOR CONFIDENCE IN THE EXTENDED 
PORTION OF THE JTWC FORECAST TRACK.//
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