WDPN32 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W 
(ATSANI) WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 23W (ATSANI), LOCATED 
APPROXIMATELY 522 NM EAST-NORTHEAST OF MANILA, PHILIPPINES, 
HAS TRACKED WESTWARD AT 17 KNOTS OVER THE PAST SIX HOURS. 
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS 
BUILDING, DENSE CONVECTION OBSCURING A LOW LEVEL CIRCULATION 
CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH FAIR 
CONFIDENCE BASED ON THE LOW LEVEL BANDING FEATURES PRESENT 
IN THE EIR LOOP AS WELL AS THE LOW LEVEL CONVECTIVE FEATURES 
PRESENT IN A 011635Z ATMS 165.5 GHZ IMAGE. THE INITIAL 
INTENSITY OF 30 KTS IS PLACED WITH FAIR CONFIDENCE BASED ON 
A DVORAK CURRENT INTENSITY ESTIMATE OF T2.0 (30 KTS) FROM 
BOTH PGTW AND RJTD. THE SYSTEM IS TRACKING ALONG THE
SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST AND THROUGH A MARGINALLY
FAVORABLE ENVIRONMENT WITH WARM (29-30 KTS) SEA SURFACE 
TEMPERATURES (SST) AND LOW (10-15 KTS) VERTICAL WIND SHEAR
(VWS) SLIGHTLY OFFSET BY A LACK OF WELL ESTABLISHED UPPER
LEVEL SUPPORT WITH ONLY WEAK EQUATORWARD OUTFLOW PRESENT. 
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, STEERED BY THE STR, AND BY TAU 24, WILL REACH 
A COL AREA SOUTH OF A SHORTWAVE MIDLATITUDE TROUGH. DURING
THIS TIME, WEAK STEERING WILL LEAD TO A QUASI-STATIONARY (QS)
TRACK AND GRADUAL INTENSIFICATION DUE TO DECREASING VWS, WARM
SST AND ENHANCED POLEWARD OUTFLOW ALOFT. THIS IMPROVEMENT IN
ENVIRONMENTAL CONDITIONS WILL LEAD TS ATSANI TO INTENSIFY TO
70 KTS BY TAU 72, ALTHOUGH THERE REMAINS THE POTENTIAL FOR 
RAPID INTENSIFICATION DEPENDING ON THE TIMING AND DEGREE OF 
THE INTERACTION BETWEEN THE AFOREMENTIONED TROUGH AND STR. 
NUMERICAL MODEL TRACK GUIDANCE IS IN FAIR AGREEMENT THROUGH 
TAU 72 WITH A MAXIMUM SPREAD OF 290 NM AT THIS TIME AND LENDS
FAIR CONFIDENCE IN THIS INITIAL PORTION OF THE JTWC FORECAST
TRACK. 
   C. IN THE EXTENDED FORECAST, TS ATSANI WILL TRACK GENERALLY
WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STEERING RIDGE 
AND THROUGH A MARGINALLY FAVORABLE ENVIRONMENT WITH LOW VWS
AND RELATIVELY WARM (26-27 CELSIUS) SST OFFSET SLIGHTLY BY 
REDUCED UPPER LEVEL SUPPORT AND CONVERGENCE ALONG THE NORTHERN
PERIPHERY OF THE SYSTEM. THESE CONDITIONS WILL ALLOW FOR 
FURTHER INTENSIFICATION TO 80KTS BY TAU 96 AT WHICH TIME THE
SYSTEM WILL MOVE BRIEFLY OVER NORTHERN LUZON, PHILIPPINES. 
AFTER TAU 96, INCREASING VWS AND COOLER SST IN THE LUZON STRAIT 
WILL GRADUALLY WEAKEN THE SYSTEM DOWN TO 70KTS BY TAU 120. 
NUMERICAL MODELS SIGNIFICANTLY DIVERGE TO OVER 252NM BY TAU 
120 WITH AFUM, NAVTGEM AND UEMN SUGGESTING A RECURVATURE INTO 
JAPAN AND THE REMAINING MEMBERS OF THE JTWC MULTI-MODEL
CONSENSUS PROVIDING A GENERALLY WESTWARD TRACK. THIS BIFURCATION
IN MODEL SOLUTIONS LENDS LOW CONFIDENCE IN THIS EXTENDED 
PORTION OF THE JTWC FORECAST TRACK.//
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