Tropical Storm KROVANH Advisory 19 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KROVANH) WARNING NR 17//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 20W (KROVANH), LOCATED APPROXIMATELY 48 NM SOUTHEAST
OF CHICHI JIMA, HAS TRACKED NORTH-NORTHEASTWARD AT 10 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED IR SATELLITE IMAGERY SHOWS CURVED
CONVECTIVE BANDING OVER THE NORTHERN SEMI-CIRCLE OF THE LOW-LEVEL
CIRCULATION CENTER (LLCC). A 181738Z NOAA-19 89GHZ IMAGE DEPICTS A
MICROWAVE EYE FEATURE WITH CURVED BANDING WRAPPING INTO THE WEST
QUADRANT OF THE LLCC. IMAGERY SUPPORTS THE CURRENT POSITION AND
TRACK MOTION WITH GOOD CONFIDENCE. UPPER-LEVEL ANALYSIS SHOWS A
MARGINALLY-FAVORABLE ENVIRONMENT WITH STRONG SOUTHWESTERLY VERTICAL
WIND SHEAR OFFSET BY VIGOROUS POLEWARD OUTFLOW. CONSEQUENTLY, THE
INITIAL INTENSITY HAS BEEN DECREASED TO 75 KNOTS BASED ON THE
DVORAK CURRENT INTENSITY ESTIMATES RANGING FROM 65 TO 90 KNOTS.
TY 20W IS TRACKING ALONG THE NORTHWESTERN PERIPHERY OF A DEEP-
LAYERED STR.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE. WIND RADII HAVE BEEN ADJUSTED
SLIGHTLY BASED ON RECENT ASCAT DATA.
   B. TY 20W WILL RE-CURVE NORTHEASTWARD THROUGH TAU 72 AS IT TRACKS
POLEWARD OF THE STR AND BEGINS TO ENCOUNTER MIDLATITUDE WESTERLIES.
TY 20W IS FORECAST TO BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY TAU
48 AS IT BECOMES EMBEDDED WITHIN THE MIDLATITUDE WESTERLIES. THE
SYSTEM SHOULD COMPLETE ETT BY TAU 96 BUT COULD COMPLETE ETT EARLIER.
DYNAMIC GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72 AND SUPPORTS
THE JTWC FORECAST TRACK WITH HIGH CONFIDENCE. TY 20W IS FORECAST
TO CONTINUE TO WEAKEN DUE TO THE STRONG VWS AND COOLER SST AFTER
TAU 48.
   C. IN THE EXTENDED TAUS, DYNAMIC GUIDANCE DIVERGES DUE TO AN
ATYPICAL SYNOPTIC PATTERN, WHICH WILL SERVE TO WEAKEN THE
MIDLATITUDE WESTERLIES, PRODUCING A SLOWER RE-CURVE SCENARIO.
BASICALLY, A MIDLATITUDE HIGH TO THE NORTH WILL RESULT IN A WEAKER
WESTERLY STEERING ENVIRONMENT BUT SHOULD STILL STEER THE SYSTEM
EASTWARD. DESPITE THE SPREAD IN THE DYNAMIC MODELS, THERE IS
HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.//
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