Tropical Storm CHABA Advisory dom, 02.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (CHABA) WARNING NR 17//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 21W (CHABA), LOCATED APPROXIMATELY 462 NM
SOUTH-SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED
NORTHWESTWARD AT 16 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS RAPIDLY
DEEPENED AND BECOME MORE SYMMETRICAL AS FEEDER BANDS WRAPPED AND
COALESCED INTO THE SUPER-DEEP CENTRAL CONVECTION. THE INITIAL
POSITION IS BASED ON A SHARPLY OUTLINED 5-NM EYE IN THE MSI LOOP WITH
HIGH CONFIDENCE. THE INITIAL INTENSITY OF 105 KNOTS IS BASED ON
AGENCY DVORAK ESTIMATES RANGING FROM T5.5 TO T6.0 AND REFLECTS THE
RAPID INTENSIFICATION. TY 21W IS TRACKING IN A VERY FAVORABLE
ENVIRONMENT WITH STRONG DIFFLUENCE ALOFT, LOW (05-10 KNOT) VERTICAL
WIND SHEAR (VWS), AND VERY WARM (30C) SEA SURFACE TEMPERATURES
(SSTS). THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF
THE DEEP-LAYERED SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. THE FORECAST PEAK INTENSITY HAS BEEN RAISED TO 130 KNOTS AND
THE TRACK HAS BEEN WIDENED FURTHER WEST OF KADENA AB AND FURTHER
NORTH ALONG THE JAPANESE ISLANDS. OTHERWISE, NO SIGNIFICANT CHANGE TO
THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING
BULLETIN.
   B. TY 21W WILL CONTINUE NORTHWEST TO NORTH-NORTHWESTWARD OVER THE
NEXT 36 HOURS TOWARDS OKINAWA. AFTERWARDS, IT WILL ROUND THE STR AXIS
AND RE-CURVE TO THE NORTHEAST. ENVIRONMENTAL CONDITIONS WILL REMAIN
FAVORABLE FOR CONTINUED INTENSIFICATION IN THE NEAR TERM, PEAKING AT
135 KNOTS BY TAU 36 PARTLY DUE TO AN APPROACHING MID-LATITUDE TROUGH
THAT WILL FURTHER ENHANCE POLEWARD OUTFLOW. JUST BEFORE TAU 72, THE
CYCLONE WILL MAKE LANDFALL OVER NORTHERN KYUSHU, JAPAN NEAR SASEBO
AND BEGIN TO WEAKEN MOSTLY DUE TO INCREASING VWS AND LAND
INTERACTION.
   C. IN THE EXTENDED FORECAST, TY CHABA WILL ACCELERATE
NORTHEASTWARD AND DRAG ACROSS THE RUGGED JAPANESE ISLAND CHAIN AND
RAPIDLY ERODE DUE TO LAND INTERACTION IN ADDITION TO STRONG (30-40
KNOT) VWS. CONCURRENTLY, THE SYSTEM WILL UNDERGO EXTRA-TROPICAL
TRANSITION (ETT) AND IS EXPECTED TO COMPLETE ETT BY THE END OF THE
FORECAST PERIOD AFTER IT TRACKS BACK INTO THE PACIFIC OCEAN SOUTH OF
MISAWA. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT UP TO TAU 36,
AFTERWARDS, IT SPREADS SIGNIFICANTLY BOTH IN TERMS OF SPEED AND
DIRECTION. IN VIEW OF THIS, THERE IS LOW CONFIDENCE IN THE JTWC TRACK
FORECAST BEYOND TAU 36.//
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