Tropical Storm PHANFONE Advisory 12月25日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (PHANFONE)
WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 30W (PHANFONE), LOCATED APPROXIMATELY 223 NM SOUTHEAST
OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 14 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED IMAGERY REVEALS A
PERSISTENT 15 NM WIDE EYE SURROUNDED BY A COLD, CONVECTIVE
EYEWALL. THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION, WHICH
IS BASED ON THE EYE. THE INITIAL INTENSITY IS ASSESSED AT 90 KTS,
BASED ON THE RJTD DVORAK CURRENT INTENSITY ESTIMATE OF T5.0 (90
KTS) AND THE PGTW AND KNES DVORAK CURRENT INTENSITY ESTIMATES OF
T5.5 (102 KTS), AND UNCERTAINTY IN THE EXACT INTENSITY AS THE
SYSTEM TRACKS ACROSS THE WATERS WITHIN THE PHILIPPINES
ARCHIPELAGO. THE ENVIRONMENT IS FAVORABLE FOR CONTINUED
DEVELOPMENT WITH LOW (5-10 KT) VERTICAL WIND SHEAR (VWS), GOOD
POLEWARD AND EQUATORWARD OUTFLOW AND WARM (27-28 CELSIUS) SEA
SURFACE TEMPERATURES (SSTS). TY 30W HAS CONTINUED TO TRACK WEST-
NORTHWESTWARD 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
96. THE FAVORABLE ENVIRONMENT IS EXPECTED TO PARTIALLY OFFSET LAND
INTERACTION THAT WILL PERSIST THROUGH TAU 18, ALLOWING THE SYSTEM
TO MAINTAIN INTENSITY AT 90 KTS. SMALL TRACK VARIATIONS TAKING THE
SYSTEM MORE OR LESS OVER LAND WILL IMPACT THE INTENSITY THROUGH
TAU 24. ONCE TY 30W EMERGES IN THE SOUTH CHINA SEA, BETWEEN TAUS
12 AND 24, IT WILL INTENSIFY TO A MAXIMUM OF 100 KTS AT TAU 36.
DUE TO THE COMPLICATED NATURE OF THE LAND INTERACTION, THERE IS
HIGH UNCERTAINTY IN THIS PORTION OF THE INTENSITY FORECAST.
COAMPS-GFS AND ECMWF INTENSITY GUIDANCE IS ABOVE THE MULTI-MODEL
CONSENSUS AND AT THE TOP OF OR ABOVE THE 70% PROBABILITY CURVE;
HOWEVER, THE GFS INTENSITY SOLUTION IS SIGNIFICANTLY BELOW THE
CONSENSUS. THE JTWC INTENSITY FORECAST IS HEDGED SLIGHTLY ABOVE
THE MULTI-MODEL CONSENSUS, TOWARDS ECMWF IN RECOGNITION OF THE
FAVORABLE ENVIRONMENT. THE MOST RECENT MODEL TRACK GUIDANCE SHOWS
DIVERGENCE AMONG SOME MODELS WITH GALWEM, UKMET, AND THE UKMET
ENSEMBLE TAKING A MORE NORTHWESTERLY TRACK THROUGH TAU 72 BEFORE
TURNING DUE WEST. THE JTWC TRACK MAINTAINS CONSISTENCY WITH
PREVIOUS TRACKS BASED ON PERSISTENCE AND THE DEEP LAYER STR TO THE
NORTHEAST THAT WILL STEER THE SYSTEM THROUGH TAU 72. BASED ON THE
DIVERGING MODEL GUIDANCE THE CONFIDENCE IN THIS PORTION OF THE
JTWC TRACK HAS DECREASED TO FAIR.
   C. AFTER TAU 72, TY 30W WILL BEGIN TO ENCOUNTER DECREASING SSTS
(25-26 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
CONTINUES TO SPREAD IN BOTH NORTH-SOUTH PLACEMENT AND ALONG TRACK
SPEED AFTER TAU 72. ALL MODELS RECURVE THE SYSTEM AROUND THE DEEP-
LAYER STEERING RIDGE THAT BUILDS BACK INTO THE AREA IN LATER TAUS,
WITH THE EXCEPTION OF GALWEM, UKMET, AND THE UKMET ENSEMBLE THAT
TRACK DUE WEST IN LATER TAUS. THE JTWC FORECAST TRACK NOW CURVES
NORTHWESTWARD AT TAU 120. THERE IS LOW CONFIDENCE IN THE LATTER
HALF OF THE JTWC FORECAST DUE TO THE LARGE MODEL SPREAD.//
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