Tropical Storm PHANFONE Advisory Sat Dec 28

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (PHANFONE) WARNING
NR 027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 30W (PHANFONE), LOCATED APPROXIMATELY
336 NM EAST-SOUTHEAST OF DA NANG, VIETNAM, HAS TRACKED WESTWARD AT
13 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY SHOWS A FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) WITH A SMALL CONVECTIVE CELL DISPLACED TO THE NORTHEAST. DUE
TO THE FULLY EXPOSED NATURE OF THE LLCC, THERE IS GOOD CONFIDENCE IN
THE INITIAL POSITION. THE INITIAL INTENSITY OF 30 KTS IS BASED ON
DVORAK CURRENT INTENSITY ESTIMATES OF T2.0 (30 KTS) BY PGTW AND
RCTP, SUPPORTED BY A 280224Z METOP-C ASCAT BULLSEYE PASS DEPICTING A
SMALL REGION OF 30-35 KT WINDS OT THE NORTHWEST. TD 30W MAINTAINS A
GOOD POLEWARD OUTFLOW CHANNEL. HOWEVER, THIS IS OFFSET BY HIGH (30-
40 KTS) VERTICAL WIND SHEAR (VWS) AND COOL (25-26 CELSIUS) SEA
SURFACE TEMPERATURES (SST) WHICH CREATE AN UNFAVORABLE ENVIRONMENT
FOR THE SYSTEM. TD 30W IS TRACKING WESTWARD ALONG THE SOUTHERN
PERIPHERY OF A SUBTROPICAL RIDGE (STR) AT 850 MB.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TD 30W WILL CONTINUE TO TRACK WESTWARD AND DISSIPATE BY TAU 24
AS THE ENVIRONMENT BECOMES LESS FAVORABLE DUE TO INCREASING VWS AND
SST COOLING BELOW 25 CELSIUS. NUMERICAL MODELS ARE IN GOOD AGREEMENT
THROUGH TAU 12 AND THEN BEGIN TO SLOWLY DIVERGE THEREAFTER. THE
UKMET ENSEMBLE AND GFS ENSEMBLE DEPICT A NORTHWESTWARD TRACK WHILE
NAVGEM HAS A SOUTHWESTWARD SOLUTION. THESE DIFFERENCES ARE
ATTRIBUTED TO THE MODEL VARIATIONS IN THE 850-700 MB FLOW WHICH IS
MAINTAINED AS THE STEERING MECHANISM FOR TD 30W AS IT WEAKENS.
THEREFORE, THE JTWC TRACK FORECAST HAS BEEN PLACED NEAR THE MULTI-
MODEL CONSENSUS, LENDING FAIR CONFIDENCE TO THE FORECAST TRACK.//
NNNN
NNNN