Tropical Storm PHANFONE Advisory Wed Dec 25

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (PHANFONE)
WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 30W (PHANFONE), LOCATED APPROXIMATELY 151 NM
SOUTH OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT
11 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL IMAGERY
REVEALS AN 20 NM WIDE CLOUD-FILLED EYE WITH THE UPPER LEVELS
DISPLACED SLIGHTLY TO THE NORTHWEST OF THE LOW-LEVEL CIRCULATION
CENTER (LLCC). THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION,
WHICH IS BASED ON THE EYE. THE INITIAL INTENSITY IS ASSESSED AT 95
KTS, HEDGING BELOW MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES
OF T5.5 (102 KTS) BASED ON THE STRUGGLING STRUCTURE; THE EYEWALL HAS
FRAGMENTED, CONVECTION HAS WEAKENED, AND THE EYE HAS COOLED. THE
ENVIRONMENT IS FAVORABLE FOR CONTINUED DEVELOPMENT WITH LOW (5-10
KT) VERTICAL WIND SHEAR (VWS), GOOD POLEWARD AND WESTWARD OUTFLOW
AND WARM (27-28 CELSIUS) SEA SURFACE TEMPERATURES (SST). BASED ON
OBSERVATIONS AND A 250111Z METOP-A ASCAT PASS, TY 30W IS A COMPACT
SYSTEM WITH LIMITED WIND RADII. TY 30W IS TRACKING ALONG THE
SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY
FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 30W WILL TRACK GENERALLY WEST-NORTHWESTWARD THROUGH TAU
48. TY 30W WILL SOON TRACK INTO THE SOUTH CHINA SEA AND MAINTAIN ITS
INTENSITY OF 95 KTS, AS SUFFICIENT SSTS AND LOW VWS ARE OFFSET BY
WANING OUTFLOW AND UPPER-LEVEL CONVERGENCE ON THE EASTERN SIDE. BY
TAU 36, TY 30W WILL BEGIN WEAKENING AS IT ENCOUNTERS DECREASING SSTS
(25-26 DEGREES CELSIUS), INCREASING VWS AND RELATIVELY COOL, DRY AIR
FROM A NORTHEASTERLY SURGE EVENT ASSOCIATED WITH A BUILDING SURFACE
HIGH PRESSURE SYSTEM TO THE NORTH. TY 30W HAS BEEN TRENDING ABOVE
MODEL INTENSITY GUIDANCE, THEREFORE THE CURRENT INTENSITY IS
MAINTAINED SLIGHTLY ABOVE THE MULTI-MODEL CONSENSUS, BUT IN LINE
WITH MESOSCALE AND STATISTICAL-DYNAMICAL MODEL GUIDANCE. BETWEEN TAU
48 AND 72, LOW-LEVEL NORTHEASTERLY SURGE WILL STEER THE SYSTEM
BRIEFLY WESTWARD. THERE IS A SPREAD OF 54 NM BETWEEN THE MODEL
TRACKS AT TAU 48, LENDING FAIR CONFIDENCE TO THIS PORTION OF THE
FORECAST TRACK.
   C. AFTER TAU 72, AN INCREASINGLY UNFAVORABLE ENVIRONMENT WILL
CAUSE RAPID WEAKENING, WITH TY 30W DISSIPATING FULLY AROUND TAU 96.
THE SYSTEM WILL CONTINUE TO TRACK WEST-NORTHWESTWARD THROUGH TAU 72,
THEN TURN SHARPLY TO THE NORTHWEST AS THE DEEP-LAYER STR BUILDS BACK
IN TO THE EAST AND STEERS THE SYSTEM NORTHWARD. ALL MODELS RECURVE
THE SYSTEM AROUND THIS DEEP-LAYER STR, WITH THE EXCEPTION OF GALWEM,
UKMET, GFS, AND JGSM THAT TRACK DUE WEST IN LATER TAUS OR STOP
TRACKING THE CIRCULATION AT TAU 96. THERE IS LOW CONFIDENCE IN THE
LATER PORTION OF THE JTWC FORECAST DUE TO THE LARGE MODEL SPREAD.//
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