WDPN32 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (ATSANI) 
WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 23W (ATSANI), LOCATED APPROXIMATELY 963 NM 
EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 12 
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) 
SATELLITE IMAGERY SHOWS A WEAK AND DISORGANIZED SYSTEM WITH FLARING 
CENTRAL CONVECTION. THE INITIAL POSITION IS PLACED WITH LOW 
CONFIDENCE BASED ON A NOTCH FEATURE IN THE EIR LOOP. THE INITIAL 
INTENSITY IS BASED ON PGTW AND RJTD DVORAK ESTIMATES OF T2.0/30KTS. 
THE ENVIRONMENT IS OVERALL UNFAVORABLE WITH MODERATE TO HIGH 
(20-25KT) VERTICAL WIND SHEAR (VWS) AND WEAK OUTFLOW ALOFT OFFSET 
ONLY SLIGHTLY BY WARM (30-31C) 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. THERE IS A NOTABLE CHANGE IN THE FORECAST TRACK PHILOSOPHY. 
THE MID-PORTION OF THE FORECAST HAS BEEN SLOWED SIGNIFICANTLY TO 
REFLECT A QUASI-STATIONARY MOTION IN THE COL ZONE BETWEEN TWO 
RIDGES SPLIT BY A TRANSITORY MIDLATITUDE TROUGH. THE INTENSITIES 
IN THE EXTENDED PORTION OF THE FORECAST HAVE ALSO BEEN GREATLY 
REDUCED.
   B. TD 23W WILL CONTINUE ON ITS CURRENT TRACK IN THE PHILIPPINE 
SEA UNDER THE SAME STR. AFTER TAU 36, A SHORTWAVE MIDLATITUDE 
TROUGH APPROACHING FROM THE NORTHWEST WILL ERODE AND SPLIT THE STR 
AND PULL THE CYCLONE POLEWARD INTO THE COL ZONE BETWEEN THE 
RIDGES. THE ENVIRONMENT IS FORECAST TO IMPROVE SLIGHTLY AS VWS 
WEAKENS IN THE COL ZONE AND POLEWARD OUTFLOW IMPROVES, LEADING TO 
A SLOW INTENSIFICATION TO 55KTS BY TAU 72. NUMERICAL MODELS ARE 
IN FAIR AGREEMENT UP TO TAU 36. AFTERWARD, NAVGEM DIVERGES TO THE 
RIGHT OF THE MODEL ENVELOPE. THERE IS FAIR CONFIDENCE IN THIS 
PORTION OF THE JTWC TRACK FORECAST WHICH IS PLACED SLIGHTLY LEFT 
OF THE MULTI-MODEL CONSENSUS TO OFFSET THE UNLIKELY NAVGEM SOLUTION 
DRIVING THE VORTEX INTO THE STR. 
   C. IN THE EXTENDED FORECAST, THE SECONDARY STR BEHIND THE 
SHORTWAVE TROUGH WILL ASSUME STEERING AND SLOWLY DRIVE TD 23W WEST-
SOUTHWESTWARD THEN 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 80KTS 
BY TAU 120. NUMERICAL MODELS SIGNIFICANTLY DIVERGE TO OVER 400NM BY 
TAU 120 WITH VARYING TRACK SPEEDS, LENDING POOR CONFIDENCE IN THE 
EXTENDED PORTION OF THE JTWC FORECAST TRACK.//
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