WDPN31 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (DOLPHIN)
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 14W (DOLPHIN), LOCATED APPROXIMATELY 651
NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTH-
NORTHEASTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MST) DEPICTS TIGHT CURVED
BANDING WRAPPING INTO AN OBSCURED LOW LEVEL CIRCULATION
CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH FAIR
CONFIDENCE BASED ON THE CONVECTIVE FEATURES IN THE MSI LOOP.
THE INITIAL INTENSITY OF 45 KTS IS PLACED WITH FAIR
CONFIDENCE BASED ON A PGTW DVORAK CURRENT INTENSITY ESTIMATE
OF T3.0 (45 KTS). THE SYSTEM CONTINUES TO EXHIBIT BOTH
TROPICAL AND SUBTROPICAL CHARACTERISTICS. THE WIND FIELD,
CONVECTIVE AND THERMAL STRUCTURES HAVE REMAINED TROPICAL
OVER THE PAST 6 HOURS, HOWEVER THE POLEWARD OUTFLOW REMAINS
STRONGLY ASSOCIATED WITH THE WESTERLY FLOW OF THE JET THAT
IS PLACED OVER HONSHU, JAPAN. SEA SURFACE TEMPERATURES (SST)
REMAIN WARM (30-31 CELSIUS) AND CONDUCIVE FOR FURTHER
DEVELOPMENT HOWEVER MODERATE (15-20KT) VERTICAL WIND
SHEAR HAS PERSISTED. THIS HIGHER VWS, ALONG WITH SUBSIDENCE
ALONG THE NORTHWEST PERIPHERY OF THE SYSTEM ASSOCIATED WITH
A SHORTWAVE TROUGH TO THE NORTH, ARE OFFSETTING THE OUTFLOW
AND WARM SSTS, RESULTING IN AN OVERALL MARGINALLY FAVORABLE
ENVIRONMENT. THE CYCLONE IS TRANSITING OUT OF THE COL BETWEEN
THE SUBTROPICAL RIDGE (STR) POSITIONED TO THE WEST AND THE
STR TO THE EAST, WHICH WILL BECOME THE PRIMARY STEERING
MECHANISM.
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
B. TS DOLPHIN WILL CONTINUE TO TRACK NORTHWARD THROUGH TAU
36 ALONG THE WESTERN PERIPHERY OF THE STEERING STR TO THE EAST
AND BEGIN A GENERALLY NORTHEASTWARD TRACK THEREAFTER UPON
ROUNDING THE STR AXIS. BY TAU 48 THE SYSTEM WILL REACH A PEAK
INTENSITY OF 60 KTS DUE TO THE CONTINUED MARGINALLY FAVORABLE
ENVIRONMENT. DURING THIS INITIAL PORTION OF THE FORECAST, THE
SYSTEM WILL LIKELY TAKE ON ADDITIONAL SUBTROPICAL CHARACTERISTICS
AS SST DECREASES, VWS INCREASES AND THE UPPER LEVEL OUTFLOW
BECOMES MORE STRONGLY ASSOCIATED WITH THE ROBUST WESTERLY FLOW
ASSOCIATED WITH THE AFOREMENTIONED JET. ENVIRONMENTAL CONDITIONS
AFTER TAU 48 WILL DEGRADE DUE TO HIGHER (30+ KTS) VWS, LEADING TO
A GRADUAL WEAKENING TO 50 KTS BY TAU 72 AT WHICH POINT THE SYSTEM
WILL COMPLETE ETT UPON BECOMING EMBEDDED IN THE DEEP WESTERLY
FLOW. NUMERICAL MODEL SOLUTIONS CONTINUE TO DIVERGE SIGNIFICANTLY
WITH GFS SOLUTIONS (BOTH ENSEMBLE AND DETERMINISTIC) BRINGING THE
VORTEX SOUTH OF HONSHU AND ECMWF, UKMET AND AFUM BRINGING THE
TRACK OVER MAINLAND JAPAN. THE JTWC FORECAST TRACK IS PLACED
BETWEEN THESE MODEL SOLUTIONS AND CLOSE TO THE MULTI-MODEL
CONSENSUS. THE LARGE DEGREE OF SPREAD IN MODEL SOLUTIONS LENDS
POOR CONFIDENCE IN THE OVERALL JTWC FORECAST TRACK.//
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