WDPN32 PGTW 030900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (ATSANI) 
WARNING NR 020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 23W (ATSANI), LOCATED APPROXIMATELY 396 NM SOUTH 
OF KADENA AB, HAS TRACKED SOUTHEASTWARD AT 05 KNOTS OVER THE PAST 
SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A 
PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH 
CONVECTION BEGINNING TO ORGANIZE, CURRENTLY FLARING NEAR THE 
ASSESSED CENTER POSITION WITH SOMEWHAT WEAKER CONVECTION BEGINNING 
TO WRAP INTO THE LLCC. THE INITIAL POSITION IS PLACED WITH FAIR 
CONFIDENCE BASED ANALYSIS OF THE LOW-LEVEL BANDING FEATURES EVIDENT 
BETWEEN THE FLARE UPS OF CONVECTION, SUPPORTED BY EXTRAPOLATION TO A 
030718Z SSMIS 91GHZ MICROWAVE IMAGE, SHOWING DEEP CONVECTION TO THE 
SOUTH, AND WEAKER CONVECTIVE BANDING WRAPPING UP THE EAST SIDE. THE 
INITIAL INTENSITY IS SET AT 35KTS BASED ON MULTI-AGENCY DVORAK 
CURRENT INTENSITY ESTIMATES OF T2.5 (35 KNOTS) FROM PGTW, KNES AND 
RJTD, AN AUTOMATED DVORAK TECHNIQUE ESTIMATE OF T2.1 AND A SATELLITE 
CONSENSUS ESTIMATE OF 40 KNOTS. THE ENVIRONMENT IS OVERALL FAVORABLE 
WITH THE SYSTEM COCOONED IN A SMALL POCKET OF LOW (5 KNOTS OR LESS) 
VWS, RADIAL OUTFLOW BEING PROVIDED BY A RECENTLY DEVELOPED POINT 
SOURCE OVERHEAD, AND WARM (27 TO 28C) SEA SURFACE TEMPERATURES 
(SST). THE SYSTEM IS CURRENTLY MOVING SOUTHEAST AS IT MOVES IN A 
CLOCKWISE LOOP IN A WEAK STEERING ENVIRONMENT 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 SLOWLY DRIFT FIRST SOUTHEAST, THEN SOUTH, THEN 
SOUTHWEST OVER THE NEXT 12-24 HOURS AS IT COMPLETES THE CLOCKWISE 
LOOPING MOTION INSIDE THE AFOREMENTIONED COL REGION. BY TAU 24, STR 
LOCATED TO THE NORTHEAST WILL BEGIN TO BUILD AND EXTEND WESTWARD, 
ACCELERATING TS 23W ONTO A MORE WESTWARD TRACK BY TAU 24, CONTINUING 
GENERALLY WESTWARD THROUGH TAU 72, WHEN IT WILL ENTER THE LUZON 
STRAIT. SLOW BUT STEADY INTENSIFICATION IS FORECAST THOUGH TAU 72, 
UNDER WEAKLY FAVORABLE CONDITIONS OF LOW (5-10 KNOTS) VWS AND 
MODERATE UPPER-LEVEL OUTFLOW, BEING SOMEWHAT OFFSET BY THAT FACT 
THAT THE SSTS ARE NOT EXCEPTIONALLY WARM AND WILL BE DECREASING AS 
THE SYSTEM MOVES WEST. NUMERICAL MODELS ARE IN FAIR AGREEMENT THOUGH 
TAU 72, WITH A 140NM SPREAD AT TAU 72, IF THE NVGM SOLUTION IS 
DISCOUNTED, AND 270NM IF NVGM IS INCLUDED IN THE GUIDANCE ENVELOPE. 
THE NAVGEM SOLUTION IS THE POLEWARD OUTLIER IN THE MULTI-MODEL 
CONSENSUS, AND TAKES THE SYSTEM OVER SOUTHERN TAIWAN BEFORE DIVING 
IT SHARPLY SOUTH TO REJOIN THE REMAINDER OF THE MODEL TRACKERS BY 
TAU 72. IN LIGHT OF THE ERRATIC AND UNLIKELY NORTHWARD MOVEMENT 
REPRESENTED BY THIS MODEL, IT IS DISCOUNTED FROM THE CONSENSUS. THE 
JTWC FORECAST LIES VERY CLOSE TO THE MULTI-MODEL CONSENSUS SOLUTION 
THROUGH TAU 72 WITH FAIR CONFIDENCE.  
   C. IN THE EXTENDED TAUS, THE PRIMARY STEERING RIDGE WILL REORIENT 
TO A MORE SOUTHWEST-NORTHEAST ORIENTATION, PUSHING THE SYSTEM ONTO A 
MORE WEST-SOUTHWESTWARD TRACK BY TAU 96. AS THE SYSTEM EXITS THE 
LUZON STRAIT, IT WILL COME UNDER INCREASING PRESSURE FROM COOLER, 
DRIER NORTHEASTERLY FLOW EXITING THE TAIWAN STRAIT, WHICH COMBINED 
WITH INCREASED VWS, DECREASED UPPER-LEVEL OUTFLOW AND MARGINAL SSTS 
(27 DEG CELSISUS), WILL STEADILY WEAKEN THE SYSTEM THROUGH TAU 120. 
THE CONSENSUS MODELS, WITH THE EXCEPTION OF NVGM, ALL CONCUR ON THE 
GENERAL SCENARIO OF A WEAKENING SYSTEM MOVING SOUTHWEST AFTER TAU 
96, BUT DIFFER SOMEWHAT ON THE DEGREE OF THE TURN AND THE SPEED OF 
THE SYSTEM, CROSS-TRACK SPREAD INCREASING TO 250NM WHILE ALONG-TRACK 
SPREAD INCREASES TO 160NM BY TAU 120. THE JTWC OFFICIAL FORECAST 
FAVORS THE ECMWF SOLUTION ON THE NORTHERN SIDE OF THE GUIDANCE 
ENVELOPE WITH LOW CONFIDENCE.// 
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