WDPN32 PGTW 191500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 17W (USAGI) WARNING NR 
12//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 17W (USAGI), LOCATED APPROXIMATELY 422 NM 
EAST-NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 
09 KNOTS OVER THE PAST SIX HOURS. STY 17W HAS RAPIDLY INTENSIFIED 
OVER THE PAST 24 HOURS WITH A 75-KNOT INCREASE IN MAXIMUM SUSTAINED 
WINDS FROM 65 TO 140 KNOTS. ANIMATED INFRARED SATELLITE IMAGERY 
DEPICTS A 15-NM ROUND EYE WITH A BANDING FEATURE OVER THE SOUTHWEST 
QUADRANT. ANIMATED WATER VAPOR IMAGERY DEPICTS RADIAL OUTFLOW, WHICH 
IS FUELING THE RECENT RI PHASE. A 190924Z WINDSAT 37H IMAGE DEPICTS 
AN INCIPIENT EYEWALL REPLACEMENT CYCLE (ERC) WITH A WEAK OUTER BAND 
NOW SURROUNDING THE EYEWALL WITH A DEFINED MOAT. THERE IS HIGH 
CONFIDENCE IN THE INITIAL POSITION BASED ON THE EYE IN IMAGERY. THE 
INITIAL INTENSITY IS BASED ON DVORAK INTENSITY ESTIMATES OF 140 
KNOTS FROM ALL AGENCIES. STY 17W IS TRACKING NORTHWESTWARD ALONG THE 
SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) THAT EXTENDS FROM 
CENTRAL CHINA INTO THE EAST CHINA SEA.
3. FORECAST REASONING.
   A. NO CHANGE FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. STY 17W IS FORECAST TO TURN WEST-NORTHWESTWARD BY TAU 24 AS 
THE SYSTEM TRACKS UNDER THE STEERING INFLUENCE OF AN EAST-
WEST ORIENTED STR. BASED ON THE 19/00Z 500MB ANALYSIS, THE STR IS 
ASSESSED AS STRONG BASED ON 25 TO 40 KNOT EASTERLY WINDS AND EXTENDS 
FROM 150E LONGITUDE WESTWARD INTO CENTRAL CHINA. THE STR IS EXPECTED 
TO MAINTAIN THROUGHOUT THE FORECAST PERIOD AND WILL DRIVE THE SYSTEM 
WESTWARD AT 10 TO 12 KNOTS SPEED THROUGH TAU 72. WITH THE EXCEPTION 
OF EGRR, DYNAMIC GUIDANCE IS IN TIGHT AGREEMENT WITH MINOR 
DIFFERENCES IN TRACK SPEED. STY 17W IS FORECAST TO MAINTAIN 
INTENSITY NEAR 140 KNOTS THROUGH TAU 12; HOWEVER, INITIAL WEAKENING 
IS EXPECTED BETWEEN TAU 12 AND TAU 24 DUE TO THE ERC. STY 17W WILL 
FURTHER WEAKEN AFTER TAU 36 AS IT BEGINS TO APPROACH TAIWAN AND 
ENCOUNTERS INCREASING LAND INTERACTION.  
   C. IN THE EXTENDED TAUS, DYNAMIC MODEL GUIDANCE REMAINS IN TIGHT 
AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST 
TRACK. STY 17W SHOULD MAKE LANDFALL NEAR HONG KONG BY TAU 72 THEN 
WEAKEN SIGNIFICANTLY AS IT SKIRTS THE SOUTHERN COAST OF CHINA.//
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