Tropical Storm TAPAH Advisory nie., 22.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (TAPAH) WARNING NR
013//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 18W (TAPAH), LOCATED APPROXIMATELY 210 NM
SOUTHWEST OF SASEBO, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 14
KNOTS OVER THE PAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH
FAIR CONFIDENCE BASED ON A 220000Z HIMAWARI VISIBLE SATELLITE IMAGE,
WHICH SHOWS A BROAD AND PARTIALLY EXPOSED LOW LEVEL CIRCULATION. THE
INITIAL INTENSITY OF 55 KNOTS IS BASED ON A DVORAK CURRENT INTENSITY
(CI) ESTIMATE OF T3.5 (55 KNOTS) FROM PGTW. ENVIRONMENTAL ANALYSIS
REVEALS THAT TS 18W IS EXPERIENCING NEUTRAL TO UNFAVORABLE (20 TO 25
KNOT) VERTICAL WIND SHEAR. THE STRONG VERTICAL WIND SHEAR HAS CAUSED
THE SYSTEM TO BEGIN TO DECOUPLE WITH THE REMAINING DEEP CONVECTION
OFFSET TO THE NORTHEAST. TS 18W CONTINUES TO HAVE A STRONG POLEWARD
OUTFLOW CHANNEL BUT LITTLE TO NO EQUATORWARD OUTFLOW. SEA SURFACE
TEMPERATURES REMAIN FAVORABLE, BETWEEN 27 AND 28 DEGREES CELSIUS. TS
18W IS TRACKING NORTH-NORTHEASTWARD WHILE UNDER THE INFLUENCE OF A
SUBTROPICAL RIDGE (STR) LOCATED TO THE EAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. THE AFOREMENTIONED STR WILL REMAIN THE PRIMARY STEERING FEATURE
IN THE SHORT TERM. AS TS 18W TRACKS AROUND THE PERIPHERY OF THE STR
THE TRACK WILL SHIFT FROM NORTH-NORTHEASTWARD TO NORTHEASTWARD.
INCREASING VERTICAL WIND SHEAR WILL CAUSE TS 18W TO STEADILY DECREASE
IN INTENSITY. BY TAU 24, INTERACTION WITH THE MIDLATITUDE WESTERLIES
AND THE BAROCLINIC ZONE WILL CAUSE TS 18W TO BEGIN EXTRATROPICAL
TRANSITION (ETT). TS 18W WILL COMPLETE ETT BY TAU 36. AFTER ETT, A
GALE FORCE WIND FIELD WILL REMAIN AND RAPIDLY TRACK NORTHEASTWARD.
DYNAMIC MODEL GUIDANCE REMAINS IN GOOD AGREEMENT THROUGH TAU 36 WITH
AN INCREASING ALONG-TRACK SPREAD BY TAU 48. THE JTWC FORECAST TRACK
IS PLACED NEAR THE MULTI-MODEL CONSENSUS. OVERALL, THERE IS HIGH
CONFIDENCE IN THE JTWC FORECAST TRACK.//
NNNN
NNNN