WDPN32 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (ATSANI) 
WARNING NR 027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 23W (ATSANI), LOCATED APPROXIMATELY 381
NM SOUTH OF KADENA AB, HAS TRACKED WESTWARD AT 12 KNOTS OVER 
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS SPIRAL BANDS OF CONVECTION WRAPPING INTO A LOW 
LEVEL CIRCULATION CENTER (LLCC) THAT IS OBSCURED BY DENSE 
CONVECTION OVER THE CENTER OF THE SYSTEM. THE INITIAL POSITION 
IS PLACED WITH HIGH CONFIDENCE BASED ON THE LOW LEVEL 
CIRCULATION FEATURES IN THE MSI LOOP AS WELL AS IN A 041934Z 
SSMI 37 GHZ IMAGE. THE INITIAL INTENSITY OF 55 KTS IS PLACED 
WITH FAIR CONFIDENCE BASED ON A PGTW DVORAK CURRENT INTENSITY
ESTIMATE OF T3.5 (55 KTS) WHICH IS IN AGREEMENT WITH A 041717
CIMSS SATELLITE CONSENSUS INTENSITY ESTIMATE OF 56 KTS. THE 
ENVIRONMENT IS FAVORABLE FOR INTENSIFICATION WITH LOW (5-10) 
KTS VERTICAL WIND SHEAR (VWS), WARM (28-29 CELSIUS) SEA 
SURFACE TEMPERATURES AND ROBUST POLEWARD AND MODERATE 
EQUATORWARD OUTFLOW ALOFT. THE STEERING ENVIRONMENT HAS 
IMPROVED OVER THE LAST 6 HOURS AND THE SYSTEM IS NOW TRACKING 
WEST-SOUTHWESTWARD ALONG THE PERIPHERY OF THE SUBTROPICAL RIDE 
POSITIONED TO THE NORTHEAST. 
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 23W HAS BEGUN ITS WESTWARD MOVEMENT AS THE STR TO THE 
NORTHEAST BUILDS IN TO THE NORTH, AND IT IS FORECAST THAT THE
SYSTEM WILL ACCELERATE ALONG THIS GENERAL WEST-NORTHWEST 
MOTION THROUGH TAU 48. THE SYSTEM IS FORECAST TO GRADUALLY 
INTENSIFY TO 70 KTS BY THIS TIME DUE TO CONTINUED LOW (10-15 
KTS) VWS, WARM SST AND UPPER LEVEL SUPPORT. AFTER TAU 48, THE 
SYSTEM WILL SLOW SOMEWHAT AS THE STR WEAKENS SLIGHTLY AND 
REORIENTS TO A MORE SOUTHWEST TO NORTHEAST ORIENTATION. BY TAU 
72 THE PRIMARY STEERING MECHANISM WILL SHIFT TO THE STR LOCATED 
OVER CENTRAL CHINA, WHICH WILL SERVE TO SHIFT THE TRACK MORE 
SOUTHWESTWARD. THIS NEW TRACK WILL BRING THE SYSTEM INTO HIGH
(30-35 KTS) VWS WHICH WILL WEAKEN THE SYSTEM INTENSITY TO 40
KTS BY TAU 72. NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD 
AGREEMENT, HOWEVER NAVGEM AND AFUM DIVERGE SIGNIFICANTLY FROM
THE MULTI-MODEL CONSENSUS. SPECIFICALLY, NAVGEM DRIVES THE 
VORTEX NORTHWARD WHILE AFUM BRINGS THE SYSTEM SOUTH TOWARDS
LUZON. AS SUCH, THIS INITIAL PORTION OF THE JTWC FORECAST
TRACK IS PLACED WITH GOOD CONFIDENCE AND IS LAID SLIGHTLY 
SOUTH OF THE JTWC MULTI-MODEL CONSENSUS IN ORDER TO OFFSET THE 
UNREALISTIC TRACKS FROM THESE MODELS.
   C. IN THE EXTENDED TAUS, THE SYSTEM WILL ENTER THE NORTHERN 
PORTION OF THE SOUTH CHINA SEA BY TAU 72 ON A GENERALLY WEST-
SOUTHWESTWARD TRACK ALONG THE SOUTHEAST PERIPHERY OF THE STR 
OVER CENTRAL CHINA. SIMULTANEOUSLY, THE COMBINATION OF 
INCREASED VWS, CONVERGENT UPPER-LEVEL FLOW, ENTRAINMENT OF 
DRIER AIR FROM THE NORTH, AND COOLER SSTS WILL COMBINE TO 
STEADILY WEAKEN THE SYSTEM TO 25 KTS BY TAU 96. AS THE SYSTEM 
WEAKENS, IT WILL COME UNDER THE STEERING INFLUENCE OF THE LOW 
TO MID-LEVEL FLOW FROM THE NORTHEAST, LEADING TO A 
SOUTHWESTWARD TRACK THAT WILL LEAD TO LANDFALL AFTER SHORTLY 
AFTER TAU 96 ALONG THE SOUTH CENTRAL COAST OF VIETNAM. 
INTERACTION WITH THE UNDERLYING TERRAIN WILL LEAD TO FURTHER 
WEAKENING AND FULL DISSIPATION OVER LAND BY TAU 120. AFTER 
DISCOUNTING THE AFOREMENTIONED NAVGEM AND AFUM OUTLIERS, THERE 
REMAINS GOOD AGREEMENT IN NUMERICAL MODEL SOLUTIONS AND AS 
SUCH THE JTWC FORECAST TRACK IS PLACED WITH GOOD CONFIDENCE 
ALONG THE MULTI-MODEL CONSENSUS THROUGH THE REMAINDER OF THE 
FORECAST PERIOD.// 
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