Tropical Storm PHANFONE Advisory 12月28日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (PHANFONE) WARNING
NR 025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 30W (PHANFONE), LOCATED APPROXIMATELY 439 NM EAST
OF DA NANG, VIETNAM, HAS TRACKED WESTWARD AT 05 KNOTS OVER THE PAST
SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY REVEALS
STRONG VERTICAL WIND SHEAR DISPLACING AN ISOLATED CONVECTIVE CELL TO
THE NORTH OF THE LOW LEVEL CIRCULATION CENTER (LLCC). THERE IS FAIR
CONFIDENCE IN THE INITIAL POSITION AS THE LLCC IS BECOMING FARTHER
REMOVED FROM THE CONVECTIVE CELL AND ONLY A PORTION OF THE CIRRUS
SHIELD IS OBSCURING THE EXACT LOCATION. THE INITIAL INTENSITY OF 45
KTS IS BASED ON DVORAK CURRENT INTENSITY ESTIMATES OF 3.0(45 KTS)
FROM PGTW AND KNES. DESPITE A GOOD POLEWARD OUTFLOW CHANNEL, THE
ENVIRONMENT IS UNFAVORABLE DUE TO HIGH (25-30 KTS) VERTICAL WIND
SHEAR (VWS), COOL (25-26 CELSIUS) SEA SURFACE TEMPERATURES (SSTS),
AND DRY AIR WRAPPING IN FROM THE WEST. TS 30W IS TRACKING ALONG THE
SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) AT 850MB.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 30W WILL CONTINUE TO TRACK GENERALLY WESTWARD AND DISSIPATE
AROUND TAU 36 AS THE ENVIRONMENT BECOMES LESS FAVORABLE WITH VWS
INCREASING TO 52 KTS AND SSTS DROPPING BELOW 25 CELSIUS BY TAU 36.
AS TS 30W WEAKENS IT IS NOW BEING STEERED BY THE 850-700MB FLOW,
WHICH SHOWS MORE VARIATION THAN THE DEEP LAYER MEAN FLOW. THEREFORE,
THERE IS HIGH UNCERTAINTY IN THE MODEL GUIDANCE WITH A SPREAD OF 114
NM AT TAU 36. THE JTWC TRACK FORECAST IS PLACED JUST NORTH OF
CONSENSUS, HEDGING TOWARD THE ECMWF AND GFS SOLUTIONS WITH LOW
CONFIDENCE DUE TO HIGH UNCERTAINTY IN THE GUIDANCE.//
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