WDPN31 PGTW 210300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (IN-FA) WARNING NR 17//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 27W (IN-FA), LOCATED APPROXIMATELY 194 NM SOUTHWEST 
OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT 16 KNOTS OVER THE 
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THE 
SYMMETRY OF THE EYE HAS IMPROVED OVER THE PAST FEW HOURS, WITH A 
CLEARLY DEFINED 15-NM DIAMETER EYE, SUPPORTING HIGH CONFIDENCE IN 
POSITIONING TY 27W. DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD SHOW 
A STEADY INTENSIFICATION WITH THE CURRENT INTENSITY ESTIMATED AT 115 
KTS. UPPER-LEVEL ANALYSIS REVEALS A FAVORABLE ENVIRONMENT WITH LOW 
VERTICAL WIND SHEAR (VWS) AND GOOD OUTFLOW WITH AN EQUATORWARD BIAS. 
TY 27W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYERED 
SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 27W IS FORECAST TO MAINTAIN A WEST NORTHWESTWARD TRACK 
THROUGH TAU 48 UNDER THE STEERING INFLUENCE OF THE DEEP LAYERED STR, 
ENTRENCHED TO THE NORTH. AFTER TAU 48, THE SYSTEM WILL BEGIN TO 
TRACK MORE POLEWARD AS IT ROUNDS THE SOUTHWEST PERIPHERY OF THE STR. 
THE SYSTEM IS EXPECTED TO MAINTAIN RELATIVELY FAST TRACK SPEEDS 
THROUGH TAU 48 WHILE INTENSIFYING TO A PEAK OF 125 KNOTS IN THE NEXT 
12 TO 24 HOURS.
   C. IN THE EXTENDED TAUS, TY IN-FA WILL BEGIN SLOWING AS IT BEGINS 
TO RE-CURVE POLEWARD IN RESPONSE TO AN APPROACHING MID-LATITUDE 
TROUGH. EXTRA-TROPICAL TRANSITION IS EXPECTED TO COMMENCE NEAR TAU 
96 AS THE SYSTEM BEGINS TO INTERACT WITH THE BAROCLINIC ZONE AND THE 
STRONG MID-LATITUDE WESTERLIES. HIGH VWS VALUES ARE EXPECTED TO 
WEAKEN THE SYSTEM AFTER TAU 72. DYNAMIC MODEL GUIDANCE REMAINS IN 
TIGHT AGREEMENT THROUGH TAU 120, LENDING TO HIGH CONFIDENCE TO THE 
JTWC TRACK FORECAST WHICH IS POSITIONED CLOSE TO THE MULTI- MODEL 
CONSENSUS.//
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