Tropical Storm CHAMPI Advisory Tue Oct 20

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (CHAMPI) WARNING NR 28//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 25W (CHAMPI), LOCATED APPROXIMATELY 209 NM SOUTH-
SOUTHWEST OF IWO TO, HAS TRACKED NORTHWARD AT 04 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MSI DEPICTS A SLIGHTLY WEAKENING ASYMMETRIC
CONVECTIVE CORE SURROUNDING A 12NM EYE WHICH SUPPORTS THE CURRENT
POSITION WITH HIGH CONFIDENCE. A 192237Z SSMIS 37 GHZ IMAGE SHOWS
THE DEEPEST CONVECTION ON THE SOUTHEASTERN SIDE OF THE LLCC, WHICH
IS INDICATIVE OF SUBSIDENCE ON THE NORTHWESTERN SIDE OF THE SYSTEM.
THE TOTAL PRECIPITABLE WATER LOOP SHOWS DRY AIR WRAPPING INTO THE
WESTERN PERIPHERY OF THE CIRCULATION WHICH, IN TURN, SLIGHTLY
ELONGATES THE CLOUD SYSTEMS STRUCTURE. THE INTENSITY REMAINS AT 100
KNOTS BASED ON DVORAK INTENSITY ESTIMATES FROM ALL REPORTING
AGENCIES. UPPER LEVEL ANALYSIS INDICATES GOOD EQUATORWARD OUTFLOW
AND LOW VWS. TY CHAMPI IS TRACKING ALONG THE WESTERN PERIPHERY OF A
DEEP-LAYERED STR EXTENSION TO THE EAST.
3. FORECAST REASONING.
   A. NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 25W WILL CONTINUE TO TRACK SLOWLY NORTH TO NORTH-
NORTHWESTWARD ALONG THE WESTERN AXIS OF THE STR EXTENSION. WHILE THE
INTENSITY WILL MAINTAIN FOR A LIMITED AMOUNT OF TIME, INCREASING VWS
WILL SLOWLY ERODE THE SYSTEM THOUGH TAU 48. THIS IS IN SPITE OF THE
SLIGHTLY INCREASED POLEWARD OUTFLOW AS THE SYSTEM ROUNDS THE STR
AXIS THOUGH TAU 48. BY TAU 72 TY 25W WILL BE ALONG THE NORTHERN
PERIPHERY OF THE STR.
   C. IN THE EXTENDED FORECAST PERIOD, TY CHAMPI WILL CONTINUE TO
ACCELERATE NORTHEASTWARD AND WEAKEN DUE TO POOR ENVIRONMENTAL
CONDITIONS WITH SSTS DROPPING BELOW 26 CELSIUS. ADDITIONALLY, THE
CYCLONE WILL START TO INTERACT WITH THE ZONAL MID-LATITUDE FLOW AND
BEGIN A WEAK EXTRA- TROPICAL TRANSITION (ETT). THE TYPHOON WILL
COMPLETE ETT BY THE END OF THE FORECAST PERIOD. DYNAMIC MODEL
GUIDANCE REMAINS IN TIGHT AGREEMENT THROUGHOUT THE FORECAST PERIOD,
LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.//
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