Tropical Storm PHANFONE Advisory sam, 04.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 18W (PHANFONE) WARNING
NR 22//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 18W (PHANFONE), LOCATED APPROXIMATELY 682 NM
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHWESTWARD AT 11 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) SHOWS A 35-NM EYE WITH SPIRAL BANDING WRAPPING INTO THE LOW-
LEVEL CIRCULATION CENTER. A 032333Z SSMIS MICROWAVE IMAGE ALSO
REVEALS A SYMMETRIC SIGNATURE WITH A WELL-DEFINED MICROWAVE EYE. THE
CURRENT POSITION IS BASED ON THE EYE FEATURE ON MSI ANIMATION,
MICROWAVE EYE WITH HIGH CONFIDENCE. THE INITIAL INTENSITY HAS
INCREASED TO 130 KNOTS BASED ON DVORAK CURRENT INTENSITY ESTIMATES
FROM PGTW AND KNES RANGING FROM 127 TO 140 KNOTS. UPPER-LEVEL
ANALYSIS INDICATES STY 18W IS LOCATED IN AN AREA OF STRONG VERTICAL
WIND SHEAR OFFSET BY VIGOROUS OUTFLOW, NAMELY THE IMPROVED POLEWARD
CHANNEL AS IT TAPS INTO THE MIDLATITUDE WESTERLIES. THIS INCREASED
POLEWARD OUTFLOW SUPPORTS THE PEAK INTENSITY OF 130 KNOTS OVER THE
PAST SIX HOURS. STY 18W IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY
OF THE SUBTROPICAL RIDGE (STR) TOWARD A LARGE BREAK IN THE STR,
POSITIONED SOUTH OF WESTERN JAPAN.
3. FORECAST REASONING.
   A. DUE TO FAVORABLE UPPER-LEVEL CONDITIONS, THE SYSTEM HAS
UPGRADED TO SUPER TYPHOON STRENGTH OVER THE PAST SIX HOURS.
OTHERWISE, THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY
FROM THE PREVIOUS PROGNOSTIC REASONING BULLETIN.
   B. STY 18W IS FORECAST TO TRACK NORTHWARD OVER THE NEXT 12 HOURS
AS IT TRACKS ALONG THE WESTERN PERIPHERY OF THE STR THEN SHOULD TURN
NORTHEASTWARD AS IT ROUNDS THE AXIS OF THE STR. BY TAU 36, THE
SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS IT INTERACTS
WITH THE MIDLATITUDE WESTERLIES. STY 18W IS EXPECTED TO RAPIDLY
COMPLETE ETT AND GAIN FRONTAL CHARACTERISTICS NEAR THE KANTO PLAIN
LENDING INCREASED UNCERTAINTY TO POSITIONING DUE TO A BROADENING LOW
PRESSURE AREA. REGARDLESS OF WHETHER THE SYSTEM IS WARM-CORE OR COLD-
CORE, STORM FORCE WINDS ARE FORECAST DUE TO THE STRONG PRESSURE
GRADIENT ENHANCED BY A STRONG BAROCLINIC ZONE OVER JAPAN. AVAILABLE
MODEL GUIDANCE HAS CONTINUED TO IMPROVE AND IN GOOD AGREEMENT OVER
THE PAST SIX HOURS; HOWEVER, DUE TO SIGNIFICANT MODEL TRACK SPEED
DIFFERENCES AND TRACK UNCERTAINTY ASSOCIATED WITH THE RAPID ETT
PROCESS, THE JTWC TRACK FORECAST LEVEL OF CONFIDENCE REMAINS LOW.//
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