Tropical Storm PHANFONE Advisory Tue Dec 24

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (PHANFONE)
WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 30W (PHANFONE), LOCATED APPROXIMATELY 384 NM EAST-
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD
AT 11 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY REVEALS AN INTERMITTENT EYE FEATURE PEEKING OUT
WITHIN A COMPACT AREA OF SUSTAINED DEEP CENTRAL CONVECTION. THERE
IS GOOD CONFIDENCE IN THE INITIAL POSITION, WHICH IS SUPPORTED BY
A WELL-DEFINED MICROWAVE EYE IN A 240432Z AMSR-2 36GHZ IMAGE. THE
INITIAL INTENSITY IS ASSESSED AT 80 KTS, IN AGREEMENT WITH THE
PGTW AND KNES DVORAK CURRENT INTENSITY ESTIMATES OF T4.5 (77 KTS)
AND A 240510Z SATCON ESTIMATE OF 82 KTS. THE ENVIRONMENT IS
FAVORABLE FOR CONTINUED DEVELOPMENT WITH LOW (10-15 KT) VERTICAL
WIND SHEAR (VWS), GOOD POLEWARD AND EQUATORWARD OUTFLOW AND WARM
(28-29 CELSIUS) SEA SURFACE TEMPERATURES (SSTS).
TY 30W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR).
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 THROUGHOUT
THE FORECAST. BETWEEN TAUS 12 AND 36, THE FAVORABLE ENVIRONMENT IS
EXPECTED TO PARTIALLY OFFSET THE LAND INTERACTION, ALLOWING THE
SYSTEM TO MAINTAIN INTENSITY AT 80 KTS. ONCE TY 30W EMERGES IN THE
SOUTH CHINA SEA, IT WILL INTENSIFY TO A MAXIMUM OF 90 KTS AT TAU
48. DUE TO THE COMPLICATED NATURE OF THE LAND INTERACTION IN THIS
FORECAST, THERE IS HIGH UNCERTAINTY IN THE INTENSITY FORECAST.
HWRF, COAMPS-GFS, COAMPS-NAVGEM, AND ECMWF INTENSITY GUIDANCE IS
SIGNIFICANTLY ABOVE THE MULTI-MODEL CONSENSUS AND AT THE TOP OF
THE 70% PROBABILITY CURVE; HOWEVER, UKMET AND GFS ARE
SIGNIFICANTLY BELOW THE CONSENSUS. DECAY SHIPS , GALWEM, AND
NAVGEM ARE ROUGHLY IN LINE WITH THE INTENSITY CONSENSUS. THE JTWC
INTENSITY FORECAST IS HEDGED SLIGHTLY ABOVE THE MULTI-MODEL
CONSENSUS, TOWARDS HWRF, ECMWF, AND THE COAMPS SOLUTIONS, IN
RECOGNITION OF THE FAVORABLE ENVIRONMENT AND EMERGING EYE. THERE
IS STRONG AGREEMENT IN THE MODEL TRACK GUIDANCE THROUGH TAU 72,
LENDING HIGH CONFIDENCE TO THIS PORTION OF THE JTWC TRACK
FORECAST. THE JTWC FORECAST TRACK IS HEDGED SLIGHTLY SOUTH OF THE
MULTI-MODEL TRACK CONSENSUS TOWARDS THE ECMWF SOLUTION.
   C. AFTER TAU 72, TY 30W WILL BEGIN TO ENCOUNTER DECREASING SSTS
(26-27 DEGREES CELSIUS), INCREASING VWS AND RELATIVELY COOL, DRY
AIR FROM A BUILDING SURFACE HIGH PRESSURE SYSTEM TO THE NORTH. AS
A RESULT, TY 30W WILL BEGIN A RAPID WEAKENING TREND. FURTHERMORE,
THE SYSTEM WILL SLOW AS IT APPROACHES A COL BETWEEN THE STEERING
STR AND A LESS PRONOUNCED STR TO THE WEST. MODEL GUIDANCE SPREADS
SIGNIFICANTLY IN BOTH NORTH-SOUTH PLACEMENT AND ALONG TRACK SPEED
AFTER TAU 72. ECMWF AND NAVGEM, WHICH MAINTAIN A MUCH HIGHER
INTENSITY THROUGHOUT THE FORECAST PERIOD, AS WELL THE UKMET
ENSEMBLE MEAN, CURVE THE SYSTEM SHARPLY TO THE NORTHWEST INTO THE
AREA OF WEAK STEERING. HOWEVER, GFS CONTINUES NORTHWESTWARD, AND
GALWEM AND UKMET CURVE THE SYSTEM WEST-SOUTHWESTWARD. THE JTWC
FORECAST TRACK IS PLACED ALONG THE MULTI-MODEL CONSENSUS AFTER TAU
72 WITH LOW CONFIDENCE, PREDICATED ON THE REASONING THAT, AS TY
30W WEAKENS, IT WILL BECOME SUBJECT TO THE STEERING INFLUENCE OF
THE LOWER LEVEL NORTHEASTERLY SURGE.//
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