Tropical Storm CHOI-WAN Advisory Tue Oct 06

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (CHOI-WAN) WARNING NR 15//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 23W (CHOI-WAN), LOCATED APPROXIMATELY 158 NM WEST-
SOUTHWEST OF MINAMI TORI SHIMA, HAS TRACKED NORTHWESTWARD AT 08
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER
(LLCC) WITH IMPROVED CONVECTIVE BANDING WRAPPING TIGHTLY INTO A
BROAD BUT DEFINED CENTER. A 052021Z WINDSAT 37GHZ IMAGE SHOWS
TIGHTLY-CURVED BANDING WRAPPING INTO A WELL-DEFINED MICROWAVE EYE
FEATURE. THE CURRENT POSITION IS BASED ON THE MSI AND MICROWAVE
IMAGERY WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT
65 KNOTS BASED ON THE HIGHER END OF DVORAK INTENSITY ESTIMATES
RANGING FROM 55 TO 65 KNOTS. UPPER-LEVEL ANALYSIS SHOWS A FAVORABLE
ENVIRONMENT WITH RADIAL OUTFLOW AND LOW VERTICAL WIND SHEAR (VWS).
ADDITIONALLY, WARM SEA SURFACE TEMPERATURES (SSTS) ARE CONDUCIVE FOR
FURTHER DEVELOPMENT. TY 23W IS TRACKING ALONG THE SOUTHWESTERN
PERIPHERY OF A DEEP-LAYERED SUB-TROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. TY CHOI-WAN IS STARTING TO ROUND THE SOUTHWESTERN PERIPHERY OF
THE STEERING STR AND IS NOW TRACKING ON A POLEWARD TRAJECTORY.
FAVORABLE ENVIRONMENTAL CONDITIONS WILL PERSIST FOR THE NEXT 24 TO
36 HOURS, ALLOWING TY 23W TO REACH A PEAK INTENSITY OF 80 KNOTS
BEFORE MOVING INTO AN UNFAVORABLE ENVIRONMENT. NEAR TAU 24, THE
SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS IT INTERACTS
WITH THE BAROCLINIC ZONE. TY 23W IS FORECAST TO WEAKEN AS IT
ENCOUNTERS STRONG VWS AND TRACKS OVER COOL SST (BELOW 26 CELSIUS).
TY CHOI-WAN WILL COMPLETE ETT AS IT GAINS FRONTAL CHARACTERISTICS BY
TAU 48 BUT WILL REMAIN A STRONG COLD-CORE LOW AS IT TRACKS NORTHWARD
WITH EXPANSIVE GALE-FORCE WINDS, WHICH SHOULD EXTEND AS FAR WEST AS
THE NORTHEAST COAST OF HONSHU. DYNAMIC MODEL GUIDANCE REMAINS IN
VERY TIGHT AGREEMENT THROUGHOUT THE FORECAST PERIOD, THEREFORE,
THERE IS HIGH CONFIDENCE IN THE JTWC TRACK FORECAST.//
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