Tropical Storm FRANCISCO Advisory Pzt, 21.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (FRANCISCO) WARNING NR 20//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 26W (FRANCISCO), LOCATED APPROXIMATELY 650 NM SOUTHEAST
OF KADENA AB, HAS TRACKED NORTH-NORTHWESTWARD AT 07 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
SHOWS A RAGGED EYE FEATURE HAS REAPPEARED WHILE THE DEEP CONVECTIVE
FEEDER BANDS HAVE LOOSENED AND SLIGHTLY INCREASED THE OVERALL WIND
FIELD. THE EYE FEATURE APPEARS VERY ELONGATED AND LACKING SYMMETRY
IN THE EIR. ADDITIONALLY, THERE IS A SLIGHT ELONGATION OCCURRING
ALONG THE NORTHEAST PERIPHERY AS THE SYSTEM APPROACHES THE STRONG
MID-LATITUDE WESTERLIES. THIS ELONGATION IS EVIDENT IN A 201758Z
TRMM IMAGE, WHICH REVEALS A DEEP CONVECTIVE BAND BEING TUGGED TO THE
NORTHEAST. THE INITIAL POSITION IS BASED ON THE EIR ANIMATION AS
WELL AS THE MICROWAVE EYE IN THE TRMM IMAGE WITH HIGH CONFIDENCE.
THE INITIAL INTENSITY OF 115 KNOTS IS ON THE HIGH END OF DVORAK
CURRENT INTENSITY ESTIMATES FROM PGTW AND KNES RANGING FROM 115 TO
102 KNOTS. UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM IS WITHIN 05
DEGREES SOUTH OF THE RIDGE AXIS AND IN AN AREA OF WEAK (5-10 KNOT)
VERTICAL WIND SHEAR (VWS). A POLEWARD OUTFLOW CHANNEL HAS ALSO
BECOME APPARENT ON ANIMATED WATER VAPOR IMAGERY. THE CYCLONE IS
TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF THE DEEP-LAYERED
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING.
   B. THROUGH TAU 24, TY 26W IS EXPECTED TO CONTINUE ALONG ITS
CURRENT TRACK UNDER THE STEERING INFLUENCE OF THE STR. AFTERWARDS,
AN EXTENSION OF THE STR IS EXPECTED TO BUILD WESTWARD AND PUSH THE
TRACK SLIGHTLY FURTHER WEST AS TY 26W BEGINS TO ROUND THE STR AXIS.
THE SYSTEM HAS BEGUN TO SLOWLY WEAKEN DUE TO COOLING SEA SURFACE
TEMPERATURES (SSTS) AND INCREASING VWS ASSOCIATED WITH THE MID-
LATITUDE WESTERLIES. HOWEVER, THE INCREASED POLEWARD OUTFLOW WILL
PARTIALLY OFFSET THE VWS AND HELP SUSTAIN THE CONVECTION, THEREBY
TEMPERING THE WEAKENING TREND.
   C. AFTER TAU 72, TY FRANCISCO WILL CREST THE STR AXIS, ALLOWING
FOR A MORE POLEWARD TRACK AND SETTING INTO A NORTHEASTWARD
RECURVATURE OVER EASTERN JAPAN. COOLING SSTS AND FURTHER INCREASING
VWS WILL AMPLIFY THE WEAKENING TREND. BY TAU 96 THE SYSTEM WILL
BEGIN EXTRA-TROPICAL TRANSITION (ETT). THE SYSTEM IS FORECAST TO
BRIEFLY TRACK OVER EASTERN JAPAN AND THEN REEMERGE OVER THE PACIFIC
OCEAN AND COMPLETE ETT BY TAU 120. NUMERIC MODEL GUIDANCE REMAINS
WIDELY SPREAD IN THE EXTENDED TAUS DUE TO VARYING SOLUTIONS TO THE
ORIENTATION AND STRENGTH OF THE STR. ALL OBJECTIVE AIDS INDICATE
SOME DEGREE OF A RECURVE SCENARIO, BUT WIDELY VARY IN THE TIGHTNESS
OF THE TURN AS WELL AS TRACK SPEED. THE CURRENT FORECAST REMAINS
CLOSE TO THE MULTI-MODEL CONSENSUS AND IS BIASED TOWARDS THE ECMWF
SOLUTION. DUE TO THE HIGH UNCERTAINTY IN THE STEERING MECHANISM AT
THE EXTENDED TAUS, THE CONFIDENCE IN THE FORECAST REMAINS LOW.//
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