WDPN32 PGTW 022100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W 
(ATSANI) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 23W (ATSANI), LOCATED APPROXIMATELY 472 NM 
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED EASTWARD AT 02 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE 
IMAGERY REVEALS THE SYSTEM HAS BECOME QUASISTATIONARY OVER THE PAST 
SIX HOURS, THE CENTRAL CONVECTION IS BECOMING DISPLACED OVER THE 
SOUTHERN SEMICIRCLE OF THE SYSTEM, HOWEVER IT CONTINUES TO PARTIALLY 
OBSCURE THE LOW LEVEL CIRCULATION (LLC) DECREASING CONFIDENCE IN THE 
EXACT POSITION. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE 
BASED ON THE LOW-LEVEL BANDING WRAPPING IN TO AN OBSCURED LLC IN THE 
EIR LOOP AND A 021721Z AMSR2 89GHZ MICROWAVE IMAGE THAT REVEALS THE 
SAME LOW-LEVEL BANDING, BUT THE EXACT CENTER POSITION IS STILL 
OBSCURED. THE INITIAL INTENSITY OF 35KTS IS BASED ON THE DVORAK 
ESTIMATES OF T2.5/35KTS FROM PGTW AND RJTD. THE ENVIRONMENT IS 
FAVORABLE WITH LOW (5-15KT) VERTICAL WIND SHEAR (VWS) AND WARM (29-
30C) SEA SURFACE TEMPERATURES (SST), HOWEVER THE UPPER LEVEL OUTFLOW 
IS LIMITED TO SINGLE-CHANNEL EQUATORWARD OUTFLOW. THE CYCLONE IS 
CURRENTLY QUASISTATIONARY LOCATED IN A COL AREA BETWEEN TWO 
SUBTROPICAL RIDGES (STR), ONE TO THE EAST-NORTHEAST AND A SECOND TO 
THE WEST-NORTHWEST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 23W WILL REMAIN QUASI-STATIONARY THROUGH TAU 48 WITH NO 
DOMINANT STEERING MECHANISM AS IT CONTINUES TO SLOWLY MEANDER AROUND 
THE COL IT IS CURRENTLY LOCATED NEAR. AROUND TAU 48 THE STR TO THE 
EAST-NORTHEAST OF THE SYSTEM WILL BUILD AND TAKE OVER AS THE PRIMARY 
STEERING MECHANISM SENDING TS 23W WESTWARD BETWEEN TAUS 48 AND 72. A 
FAVORABLE ENVIRONMENT CONSISTING OF LOW (5-15KT) VWS, WARM (28C) 
SST, AND DECENT UPPER LEVEL OUTFLOW TO THE WEST WILL PROMOTE STEADY 
INTENSIFICATION TO A PEAK OF 65 KTS AT TAU 72. ALTHOUGH THERE HAVE 
BEEN INDICATIONS OF THE POTENTIAL FOR RAPID INTESIFICATION THE QUASI-
STATIONARY NATURE OF THE SYSTEM CHURNING UP COOLER WATER BENEATH THE 
SURFACE WILL LIKELY INHIBIT THE ABILITY OF THE SYSTEM TO RAPIDLY 
INTENSIFY. 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 STEER TS 23W WEST-
NORTHWESTWARD THROUGH THE LUZON STRAIT, AND INTO THE SOUTH CHINA SEA 
(SCS) TURNING TO THE WEST-SOUTHWEST BETWEEN TAUS 96 AND 120. THE 
ENVIRONMENT WILL DETERIORATE DUE TO DECREASED DIVERGENCE ALOFT AND 
COOLING SST IN THE SCS, WEAKENING THE SYSTEM TO 45KTS BY TAU 120. 
NUMERICAL MODELS SIGNIFICANTLY DIVERGE WITH A SPREAD OF 600 NM BY 
TAU 120 WITH ECMWF AND UEMN SUGGESTING A RECURVATURE INTO TAIWAN, 
LENDING LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST 
THAT IS LAID WITH THE MAIN CLUSTER OF THE MODEL ENVELOPE.// 
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