WDPN32 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W 
(ATSANI) WARNING NR 015//
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 MULTISPECTRAL SATELLITE IMAGERY (MSI) 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 012221Z SSMIS 37 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 AND 
CONVERGENCE ALONG THE NORTHERN PERIPHERY OF THE SYSTEM. 
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 12, 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 TD ATSANI TO INTENSIFY TO
50 KTS BY TAU 48, ALTHOUGH THERE REMAINS THE POTENTIAL FOR 
RAPID INTENSIFICATION DEPENDING ON THE TIMING AND DEGREE OF 
THE INTERACTION BETWEEN THE AFOREMENTIONED TROUGH AND STR. AS
THE STEERING RIDGE TO THE EAST BUILDS WESTWARD, IT WILL BEGIN
TO DRIVE THE SYSTEM WESTWARD THROUGH TAU 72 DURING WHICH TIME
TD ATSANI WILL FURTHER INTENSIFY TO 65 KTS. NUMERICAL MODEL 
TRACK GUIDANCE IS IN FAIR AGREEMENT THROUGH TAU 72 WITH A 
MAXIMUM SPREAD OF 147 NM AT THIS TIME AND LENDS FAIR 
CONFIDENCE IN THIS INITIAL PORTION OF THE JTWC FORECAST TRACK. 
   C. IN THE EXTENDED FORECAST, TD 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 75 KTS BY TAU 96 AT WHICH TIME THE
SYSTEM WILL TRACK THROUGH THE LUZON STRAIT. AFTER TAU 96, 
INCREASING VWS AND COOLER SST WILL GRADUALLY WEAKEN THE SYSTEM 
TO 70 KTS BY TAU 120. NUMERICAL MODELS SIGNIFICANTLY DIVERGE TO 
OVER 682 NM BY TAU 120 WITH NAVGEM AND UEMN SUGGESTING A 
RECURVATURE SCENARIO INTO TAIWAN AND THE REMAINING MEMBERS OF 
THE JTWC MULTI-MODEL CONSENSUS PROVIDING A GENERALLY WESTWARD 
TO NORTHWESTWARD TRACK. THIS BIFURCATION IN MODEL SOLUTIONS IS
LIKELY DUE TO THE TIMING AND EXTENT OF THE STR REORIENTATION 
AS IT BUILDS WESTWARD TOWARDS CHINA. THIS UNCERTAINTY IN MODEL
SOLUTIONS LENDS LOW CONFIDENCE IN THIS EXTENDED PORTION OF THE 
JTWC FORECAST TRACK.//
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