Tropical Storm DOLPHIN Advisory Thu Sep 24

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (DOLPHIN) WARNING
NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 14W (DOLPHIN), LOCATED APPROXIMATELY 205
NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD
AT 16 KNOTS OVER THE PAST SIX HOURS. DESPITE INCREASING VERTICAL
WIND SHEAR (VWS) OF 30 KNOTS, ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A CONSOLIDATED SYSTEM WITH DEEP CONVECTIVE BANDING
WRAPPING INTO THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 230726Z
SSMIS 91GHZ IMAGE REVEALS TIGHTLY-CURVED BANDING WRAPPING INTO THE
LLCC BUT ALSO SHOWS A WEAK FRONTAL STRUCTURE FORMING AND POSSIBLE
TILT. THE HYBRID (SUBTROPICAL) SYSTEM IS EMBEDDED WITHIN THE
SUBTROPICAL WESTERLIES BUT HAS MAINTAINED A STRONG POLEWARD OUTFLOW
CHANNEL AND WARM (29C) SST VALUES TO OFFSET THE STRONG VWS.
THEREFORE, THE SYSTEM'S CONVECTIVE STRUCTURE HAS STRENGTHENED OVER
THE PAST SIX HOURS AND NOW APPEARS TO BE MORE TROPICAL IN NATURE.
THE INITIAL INTENSITY REMAINS ASSESSED AT 50 KNOTS BASED ON A PGTW
SUBTROPICAL FIX OF ST3.0 (45-50 KNOTS) AND A RJTD DVORAK INTENSITY
ESTIMATE OF T3.5 (55 KNOTS). A RECENT ASCAT IMAGE SHOWED AN
EXPANSIVE REGION GALE-FORCE WINDS TO THE NORTH WITH AN ELONGATED
CENTER AND MAXIMUM WINDS OF 45-50 KNOTS. SURFACE OBSERVATIONS FROM
CHICHI-JIMA (33.1N 139.8E), ABOUT 96NM NORTHEAST, INDICATE EAST-
NORTHEASTERLY WINDS AT 26 TO 30 KNOTS. TS 14W IS TRACKING
NORTHEASTWARD ALONG THE NORTHERN PERIPHERY OF THE SUBTROPICAL RIDGE
(STR) WITHIN THE SUBTROPICAL WESTERLIES.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 14W IS ACCELERATING WITHIN THE SUBTROPICAL WESTERLIES AND
IS FORECAST TO CONTINUE TRACKING NORTHEASTWARD TO NORTH-
NORTHEASTWARD THROUGH THE FORECAST PERIOD. NUMERICAL MODEL GUIDANCE
IS IN TIGHT AGREEMENT THROUGH TAU 24 WITH A 36NM SPREAD IN SOLUTIONS
AT TAU 24 BUT DIVERGES SIGNIFICANTLY AFTER TAU 24 WHEN THE SYSTEM
UNDERGOES EXTRA-TROPICAL TRANSITION (ETT) EAST OF NORTHERN HONSHU.
TS 14W SHOULD COMPLETE ETT BY TAU 36. AS MENTIONED PREVIOUSLY, THE
SYSTEM HAS RE-CONSOLIDATED DESPITE THE SUBTROPICAL AND BAROCLINIC
INFLUENCES ON THE SYSTEM. THERE IS SOME UNCERTAINTY IN THE PEAK
INTENSITY, AT LEAST OVER THE NEXT 12 HOURS, UNTIL VWS INCREASES TO
35-40 KNOTS. BY TAU 24, VWS WILL INCREASE TO 40-50 KNOTS, WHICH WILL
LEAD TO A WEAKENING TREND. BASED ON THE MODEL SPREAD AFTER TAU 24
AND POSITIONAL UNCERTAINTY, THERE IS NOW MODERATE CONFIDENCE IN THE
JTWC FORECAST TRACK.//
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