Tropical Storm DOLPHIN Advisory Paz, 20.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (FOURTEEN)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 14W (FOURTEEN), LOCATED APPROXIMATELY
366NM EAST-SOUTHEAST OF KADENA AB, HAS TRACKED NORTH-NORTHWESTWARD
AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY DEPICTS SYMMETRIC, CENTRAL CONVECTION
OBSCURING A LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE LOW LEVEL
CIRCULATION (LLC) EVIDENT IN WIND FIELD DATA FROM A TIMELY 201053Z
ASCAT-A PASS. THE INITIAL INTENSITY OF 35 KTS IS ALSO PLACED WITH
HIGH CONFIDENCE BASED ON THE 35 KTS WINDS PRESENT ALONG THE EASTERN
PERIPHERY OF THE LLC IN THE ASCAT-A DATA AND IS HEDGED SLIGHTLY
HIGHER THAN MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T2.0
(30 KTS, PGTW AND KNES). THE SYSTEM HAS SUBTROPICAL CHARACTERISTICS.
THE INTENSITY OF THE WIND FIELD, FOR EXAMPLE, IS HIGHLY ASYMMETRIC
WITH HIGH (30+ KTS) WINDS ALONG THE EASTERN PERIPHERY AND WEAKER
(15 KTS) WINDS ALONG THE WESTERN PERIPHERY. FURTHERMORE, THE OUTFLOW
FROM THE SYSTEM HAS ALREADY TAPPED INTO THE DEEP WESTERLY FLOW
ASSOCIATED WITH THE JET OVER HONSHU, JAPAN. DESPITE THIS, ANALYSIS
OF THE WIND FIELD AND THERMAL PROFILE REVEALS THAT THE SYSTEM
MAINTAINS MOSTLY TROPICAL CHARACTERISTICS. ENVIRONMENTAL ANALYSIS
FURTHER REVEALS AN ENVIRONMENT THAT IS FAVORABLE FOR DEVELOPMENT WITH
LOW (10-15 KTS) VERTICAL WIND SHEAR, WARM (30-31 CELSIUS) SEA SURFACE
TEMPERATURES (SST) AND WELL ESTABLISHED POLEWARD AND EQUATORWARD
OUTFLOW ALOFT. THE SYSTEM IS NEARLY QUASISTATIONARY AND IS TRACKING
THROUGH A WEAK STEERING ENVIRONMENT DUE TO ITS PLACEMENT INSIDE A
COL REGION THAT IS INDUCED BY A SUBTROPICAL RIDGE (STR) POSITIONED
TO THE EAST AND A SECOND STR POSITIONED TO THE WEST-SOUTHWEST.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING MESSAGE FOR THIS
SYSTEM AND SETS THE FORECAST PHILOSOPHY.
   B. TS 14W WILL CONTINUE TRACKING GENERALLY NORTHWARD UNDER THE
INFLUENCE OF THE TWO AFOREMENTIONED STEERING RIDGES. THE SYSTEM WILL
POSSIBLY TAKE ON ADDITIONAL SUBTROPICAL CHARACTERISTICS DURING THIS
TIME, HOWEVER THE FAVORABLE CONDITIONS WILL ALLOW IT TO INTENSIFY TO
55 KTS BY 24. INCREASING VWS AFTER TAU 24 WILL STIFLE FURTHER
INTENSIFICATION, HOWEVER THE ENVIRONMENT WILL REMAIN OVERALL FAVORABLE
THROUGH TAU 36 AND ALLOW THE SYSTEM TO MAINTAIN 55 KTS INTENSITY.
BY TAU 48 INCREASING (20+ KTS) VWS WILL LEAD TO A GRADUAL WEAKENING
TREND TO 50 KTS. ADDITIONALLY, THE SYSTEM WILL BEGIN TO ROUND THE STR
TO THE EAST WHICH WILL THEREAFTER BE THE PRIMARY STEERING MECHANISM.
AFTER TAU 48 THE SYSTEM WILL INTERACT FURTHER WITH THE AFOREMENTIONED
WESTERLY FLOW ALOFT AND WILL BEGIN EXTRATROPICAL TRANSITION (ETT).
AS IT CONTINUES TO TRACK GENERALLY NORTHEASTWARD AFTER THIS TIME, IT
WILL BECOME FURTHER EMBEDDED IN THE WESTERLY FLOW AND CONTINUE ETT.
NUMERICAL MODEL GUIDANCE IS IN POOR OVERALL AGREEMENT WITH A 550 NM
SPREAD IN ACROSS TRACK SOLUTIONS BY TAU 72. THE SPREAD IN MODEL
SOLUTIONS IS LIKELY DUE TO UNCERTAINTY IN THE TIMING OF AN INCOMING
SHORTWAVE TROUGH PROPAGATING FROM THE NORTHWEST THAT TEMPORARILY
ERODES THE STEERING RIDGES. THIS SPREAD IN MODEL SOLUTIONS LENDS
OVERALL POOR CONFIDENCE IN THE INITIAL PORTION OF THE JTWC FORECAST
TRACK.
   C. AFTER TAU 72 THE SYSTEM WILL CONTINUE TO TRACK ALONG THE WEST-
NORTHWESTERN PERIPHERY OF THE STR POSITIONED TO THE EAST. BY TAU 96
IT WILL BECOME FULLY EMBEDDED IN THE BAROCLINIC ZONE AND COMPLETE ETT.
THE INTENSITY IS FORECAST TO WEAKEN TO 40 KTS BY THIS TIME. NUMERICAL
MODEL SOLUTIONS CONTINUE TO DIVERGE FURTHER WITH A SPREAD OF 630 NM BY
TAU 96. THIS CONTINUED HIGH DEGREE OF SPREAD IN SOLUTIONS LENDS POOR
CONFIDENCE IN THE OVERALL JTWC FORECAST TRACK.  //
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