Tropical Storm CHABA Advisory lun, 03.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (CHABA) WARNING NR 21//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 21W (CHABA), LOCATED APPROXIMATELY 157 NM SOUTH OF KADENA
AB, OKINAWA, JAPAN, HAS TRACKED NORTHWESTWARD AT 13 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS
THE SYSTEM HAS REGAINED SYMMETRY AND A SHARPLY OUTLINED 7-NM EYE AS
THE CENTRAL CONVECTION FURTHER DEEPENED. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE EYE IN THE MSI LOOP. THE
INITIAL INTENSITY OF 125 KNOTS IS BASED ON CONGRUENT DVORAK ESTIMATES
OF T6.0 FROM SATCON AND ALL REPORTING AGENCIES. ENVIRONMENTAL
CONDITIONS REMAIN FAVORABLE WITH WARM (30C) SSTS, LOW TO MODERATE
(10-15 KNOT) VERTICAL WIND SHEAR (VWS), AND EXCELLENT RADIAL OUTFLOW
WITH A STRONG BIAS ON THE POLEWARD CHANNEL. THE CYCLONE IS TRACKING
ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE
(STR).
3. FORECAST REASONING.
   A. NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING BULLETIN.
   B. TY CHABA WILL TRACK NORTHWEST THEN NORTHWARD OVER THE NEXT 24
HOURS. AFTERWARD, THE SYSTEM WILL ROUND THE STEERING STR AND BEGIN TO
TRACK AND ACCELERATE NORTHEASTWARD THROUGH THE TSUSHIMA STRAIT INTO
THE SEA OF JAPAN (SOJ), THEN ACROSS NORTHERN HONSHU BEFORE EXITING
INTO THE NORTHWEST PACIFIC OCEAN EAST OF MISAWA BEFORE TAU 72. THE
ENVIRONMENT WILL REMAIN FAVORABLE FOR FURTHER DEVELOPMENT OVER THE
NEXT 12 HOURS - ENHANCED BY INCREASED POLEWARD OUTFLOW - LEADING TO A
PEAK OF 135 KNOTS. AFTER TAU 12, INCREASING VWS, COLDER SSTS IN THE
SOJ, THEN LAND INTERACTION WITH THE RUGGED TERRAIN OF NORTHERN HONSHU
WILL CAUSE GRADUAL THEN RAPID DECAY. BY TAU 48, THE SYSTEM WILL
UNDERGO EXTRA-TROPICAL TRANSITION (ETT) AS IT GETS EMBEDDED IN THE
BAROCLINIC ZONE. BY TAU 72, TY 21W WILL BE REDUCED TO 35 KNOTS,
POSSIBLY WEAKER, AS A COLD CORE LOW. DYNAMIC MODEL GUIDANCE IS IN
GOOD AGREEMENT; HOWEVER, THE TIMING OF THE RECURVE TOWARD THE
NORTHEAST AND EVENTUAL LANDFALL IS STILL UNCERTAIN. THEREFORE, THERE
IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST BEYOND TAU 24.//
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