Tropical Storm DUJUAN Advisory Cu, 25.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (DUJUAN) WARNING NR
13//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 21W (DUJUAN), LOCATED APPROXIMATELY 517 NM
SOUTH-SOUTHEAST OF KADENA AB, HAS TRACKED NORTHWESTWARD AT 03 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH TIGHTLY-CURVED BANDING
WRAPPING INTO AN ELONGATED BUT DEFINED CENTER. A 241622Z GCOM 37GHZ
IMAGE SHOWS MULTIPLE CONVECTIVE BANDS WRAPPING INTO THE LOW-LEVEL
CIRCULATION CENTER WITH A DEFINED MICROWAVE EYE FEATURE, THEREFORE,
THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION AND RECENT TRACK
MOTION. ANIMATED WATER VAPOR IMAGERY REVEALS SIGNIFICANTLY IMPROVED
OUTFLOW, ESPECIALLY OVER THE EASTERN SEMI-CIRCLE, DUE TO DECREASED
VERTICAL WIND SHEAR. THE INITIAL INTENSITY IS ASSESSED AT 55 KNOTS,
HEDGED HIGHER THAN THE DVORAK ESTIMATES OF T3.0 (45 KNOTS) BASED ON
THE CONVECTIVE STRUCTURE. TS DUJUAN IS TRACKING SLOWLY ALONG THE
SOUTHWESTERN PERIPHERY OF A DEEP LAYERED SUB-TROPICAL RIDGE (STR)
WITHIN A WEAK STEERING ENVIRONMENT.
3. FORECAST REASONING.
   A. NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. RECENT 500MB ANALYSES DEPICT A SHORTWAVE TROUGH OVER WESTERN
JAPAN WITH A BREAK IN THE STR NEAR OKINAWA. THE ANALYSES ALSO
INDICATE THAT THE WESTERN STR IS BUILDING INTO THE EAST CHINA SEA AS
THE SHORTWAVE TROUGH PROPAGATES EASTWARD OVER THE EASTERN STR.
FURTHERMORE, THE UPPER-LEVEL FLOW OVER ASIA IS ZONAL, WHICH SHOULD
ALLOW THE STR TO CONTINUE TO BUILD NORTH OF THE SYSTEM, RE-
ESTABLISHING THE DOMINANT STEERING INFLUENCE. TS 12W SHOULD CONTINUE
TRACKING NORTHWESTWARD TO WEST-NORTHWESTWARD THROUGH TAU 72. DYNAMIC
MODEL GUIDANCE IS IN GOOD AGREEMENT WITH SOME DIFFERENCES IN TRACK
SPEED AND TIMING OF THE WESTWARD TURN, HOWEVER, GUIDANCE (INCLUDING
ENSEMBLE GUIDANCE) HAS IMPROVED SIGNIFICANTLY AND HAS REMAINED
CONSISTENT OVER THE PAST DAY. AFTER TAU 24, TS 21W IS FORECAST TO
RAPIDLY INTENSIFY AFTER TAU 12 TO A PEAK INTENSITY OF 115 KNOTS BY
TAU 72.
   C. IN THE EXTENDED TAUS, TS 21W WILL TURN WESTWARD AS IT BEGINS
TO TRACK UNDER THE STEERING INFLUENCE OF THE WESTERN STR. DYNAMIC
GUIDANCE HAS IMPROVED WITH THE MAJORITY OF MODELS NOW SHOWING A
WESTWARD TRACK NEAR TAIWAN, HOWEVER, THERE IS UNCERTAINTY IN THE
EXACT LANDFALL POINT WITH SOLUTIONS RANGING FROM CENTRAL TAIWAN TO
NEAR 28N. TS 21W IS EXPECTED TO WEAKEN AS IT APPROACHES TAIWAN DUE
TO LAND INTERACTION AND WILL BEGIN DISSIPATING RAPIDLY AS IT TRACKS
INTO CHINA. OVERALL, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST
TRACK DUE TO TRACK UNCERTAINTY, MAINLY AFTER TAU 72.//
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