Tropical Storm PHANFONE Advisory Wed Oct 01

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (PHANFONE) WARNING
NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 18W (PHANFONE), LOCATED APPROXIMATELY 117 NM
NORTHEAST OF SAIPAN, HAS TRACKED NORTHWESTWARD AT 16 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THE
SYSTEM HAS SLIGHTLY UNRAVELED AS CONVECTIVE BANDS HAD BECOME EVEN
MORE FRAGMENTED. THE INITIAL POSITION IS BASED ON THE WELL-DEFINED
LOW LEVEL CIRCULATION EVIDENT IN THE ABOVE ANIMATION WITH FAIR
CONFIDENCE. THE INITIAL INTENSITY OF 40 KNOTS IS AVERAGED FROM DVORAK
ESTIMATES FROM PGTW, KNES, AND RJTD. UPPER-LEVEL ANALYSIS INDICATES
FAVORABLE CONDITIONS FOR FURTHER DEVELOPMENT, INCLUDING RIDGING
ALOFT, LOW VERTICAL WIND SHEAR (VWS), AND A TROPICAL UPPER
TROPOSPHERIC TROUGH TO THE WEST ENHANCING OUTFLOW. THE SYSTEM
CONTINUES TO TRACK ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYERED
SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 18W WILL TRACK WEST-NORTHWESTWARD ALONG THE SOUTHWESTERN
PERIPHERY OF THE STR THROUGH TAU 72. THE SYSTEM IS EXPECTED TO RESUME
STEADY INTENSIFICATION AS IT PASSES OVER VERY WARM WATER AND AS
UPPER-LEVEL CONDITIONS REMAIN FAVORABLE.
   C. AFTER TAU 72, TS PHANFONE IS EXPECTED TO TURN POLEWARD AS A
DEVELOPING MID-LATITUDE TROUGH INDUCES A WEAKNESS IN THE STR. BY TAU
120, THE CYCLONE WILL BEGIN EXTRA-TROPICAL TRANSITION AS IT ENTERS
THE COLD BAROCLINIC ZONE. THE INITIAL EXPOSURE OF THE SYSTEM INTO THE
MID-LATITUDE WESTERLIES WILL INCREASE POLEWARD OUTFLOW AND INTENSIFY
18W TO A PEAK OF 115 KNOTS BEFORE STRONG VWS TAKES ITS TOLL.
AVAILABLE NUMERIC GUIDANCE IS IN GOOD AGREEMENT WITH GFDN AS THE SOLE
LEFT OUTLIER. THE JTWC TRACK FORECAST IS LAID CLOSE TO THE
MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE.//
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