Tropical Storm DUJUAN Advisory Fri Sep 25

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (DUJUAN) WARNING NR 14//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 21W (DUJUAN), LOCATED APPROXIMATELY 501 NM SOUTH-
SOUTHEAST OF KADENA AB, HAS TRACKED NORTH-NORTHWESTWARD AT 03
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH TIGHTLY-CURVED BANDING
WRAPPING INTO AN 18-NM RAGGED EYE WHILE A 242245Z SSMIS 37GHZ
IMAGE SHOWS A DEFINED MICROWAVE EYE FEATURE. OVERALL, 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 65 KNOTS, HEDGED
HIGHER THAN THE DVORAK ESTIMATES OF T3.5 (55 KNOTS) BASED ON THE
CONVECTIVE STRUCTURE AND SATCON ESTIMATE OF 70 KNOTS. TY 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. TY 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. TY 21W IS FORECAST TO RAPIDLY
INTENSIFY AFTER TAU 12 TO A PEAK INTENSITY OF 115 KNOTS BY
TAU 48.
   C. IN THE EXTENDED TAUS, TY 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. TY 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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