Tropical Storm PHANFONE Advisory Fri Oct 03

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (PHANFONE) WARNING NR 15//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 18W (PHANFONE), LOCATED APPROXIMATELY 346 NM SOUTH-
SOUTHWEST OF IWO TO, HAS TRACKED WEST-NORTHWESTWARD AT 08 KNOTS OVER
THE PAST SIX HOURS. THE CURRENT POSITION IS BASED, WITH HIGH
CONFIDENCE, ON A RECENT SATELLITE EYE FIX FROM PGTW. THE INTENSITY
OF 115 KNOTS IS CONSISTENT WITH RECENT DVORAK T-NUMBER ESTIMATES OF
6.0 FROM PGTW, KNES, AND RJTD. TY 18W HAS INTENSIFIED OVER THE PAST
SIX HOURS. ALTHOUGH ERRATIC EYE MOVEMENT WAS OBSERVED IN ANIMATED
MULTISPECTRAL SATELLITE IMAGERY, THE CYCLONE CIRCULATION CONTINUES
TO MOVE ALONG A GENERALLY WEST-NORTHWESTWARD TRACK UNDER THE
STEERING INFLUENCE OF AN EXTENSIVE SUBTROPICAL RIDGE. STRONG
WESTWARD AND POLEWARD OUTFLOW AND LOW VERTICAL WIND SHEAR ARE AIDING
INTENSIFICATION.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING BULLETIN. HOWEVER, FORECAST TRACK
SPEEDS DURING THE EXTENDED FORECAST PERIOD - TAU 72 THROUGH TAU 120 -
HAVE INCREASED BASED ON A SHIFT IN THE NUMERICAL MODEL GUIDANCE AND
EXPECTATIONS THAT ACCELERATION INTO THE MIDLATITUDE WESTERLY FLOW
PATTERN WILL OCCUR VERY QUICKLY.
   B. TY 18W IS EXPECTED TO TURN POLEWARD OVER THE NEXT 48 HOURS AS
A MIDLATITUDE TROUGH ANALYZED OVER EAST ASIA TRANSLATES EASTWARD AND
INDUCES A BREAK IN THE SUBTROPICAL STEERING RIDGE. THE CYCLONE SHOULD
CREST THE RIDGE AXIS AND BEGIN ITS NORTHEASTWARD RECURVATURE BY TAU
72, COMMENCING EXTRATROPICAL TRANSITION AS IT BEGINS TO INTERACT
WITH THE APPROACHING MIDLATITUDE TROUGH. CONSENSUS NUMERICAL MODEL
TRACK FORECAST GUIDANCE IS IN FAIR AGREEMENT REGARDING THE LOCATION
AND TIMING OF THIS POLEWARD TURN. ECMWF AND JGSM CARRY THE SYSTEM A
BIT FARTHER TO THE WEST THAN THE OTHER MODELS BY TAU 72, ALTHOUGH THE
ECMWF TRACK HAS TRENDED EASTWARD TOWARD THE MAIN MODEL GROUPING IN
THE LATEST RUN. GIVEN THE CURRENT SYNOPTIC PATTERN AND GOOD AGREEMENT
AMONG A MAJORITY OF THE MODEL SOLUTIONS, THE CURRENT TAU 00-72 TRACK
FORECAST LIES NEAR THE MULTI-MODEL CONSENSUS AND IS CONSISTENT WITH
THE PREVIOUS FORECAST. THERE IS HIGH CONFIDENCE IN THIS PORTION OF
THE TRACK FORECAST. FAVORABLE UPPER-LEVEL CONDITIONS AND PASSAGE
OVER VERY WARM WATER SHOULD ALLOW TY 18W TO INTENSITY FURTHER IN
THE NEXT 12 TO 24 HOURS BEFORE THE APPROACHING TROUGH AND ASSOCIATED
WESTERLY VERTICAL WIND SHEAR BEGIN TO INFLUENCE THE SYSTEM.
   C. IN THE EXTENDED FORECAST PERIOD, TY 18W IS EXPECTED TO MERGE
WITH THE APPROACHING MIDLATITUDE TROUGH, ACCELERATE EAST-
NORTHEASTWARD, AND COMPLETE EXTRATROPICAL TRANSITION. THE TRANSITION
INTO A STRONG EXTRATROPICAL LOW IS EXPECTED TO OCCUR RATHER RAPIDLY
AS THE CYCLONE PASSES TO THE SOUTH AND EAST OF HONSHU. AN EXPANSION
OF THE WIND FIELD, INCLUDING GALE AND STORM FORCE WINDS, IS
ANTICIPATED AS THE SYSTEM COMPLETES THIS TRANSITION. NUMERICAL MODEL
GUIDANCE IS IN GENERALLY GOOD AGREEMENT REGARDING TRACK DIRECTION IN
THE EXTENDED PERIOD, BUT TRACK SPEEDS VARY WIDELY AMONG THE MODELS.
THE CURRENT SYNOPTIC PATTERN FAVORS DEVELOPMENT OF VERY STRONG UPPER-
LEVEL WESTERLY FLOW ACROSS AND TO THE SOUTHEAST OF HONSHU, SO THE
CURRENT FORECAST FAVORS RAPID ACCELERATION AND LIES NEAR THE MULTI-
MODEL CONSENSUS. HOWEVER, GIVEN LARGE VARIATIONS IN MODEL DEPICTIONS
OF TRACK SPEED, THERE IS LOW CONFIDENCE IN THE EXTENDED TRACK
FORECAST. ALTHOUGH INTERACTION BETWEEN THE BAROCLINIC ZONE AND 18W
WILL INDUCE RAPID WEAKENING EARLY IN THE EXTENDED FORECAST PERIOD,
IT WILL ULTIMATELY BE FAVORABLE ENOUGH TO SUPPORT TRANSITION INTO A
STORM FORCE LOW BY TAU 120.//
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