Tropical Storm MALAKAS Advisory Sat Sep 17

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (MALAKAS) WARNING NR 24//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 18W (MALAKAS), LOCATED APPROXIMATELY 276 NM WEST OF
KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWARD AT 07 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS
THE SYSTEM HAS BECOME MORE ASYMMETRICAL AND ELONGATED WITH SHALLOWER
CONVECTION. THE INITIAL POSITION IS BASED ON A LOW REFLECTIVITY
MICROWAVE EYE IN THE 171006Z 37GHZ SSMIS PASS AND ALSO REFLECTED AS
AN EYE FEATURE ON A COMPOSITE RADAR REFLECTIVITY LOOP FROM
MIYAKOJIMA, JAPAN. THE INITIAL INTENSITY OF 100 KNOTS IS BASED ON AN
OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK ESTIMATES AND
REFLECTS THE WEAKENED STATE. UPPER-LEVEL ANALYSIS INDICATES TY 18W
HAS DRIFTED INTO THE PREVAILING WESTERLIES. AS SUCH, POLEWARD OUTFLOW
HAS INCREASED AND WITH EQUATORWARD OUTFLOW REMAINING ROBUST,
VENTILATION OF THE CENTRAL CONVECTION IS ENHANCED. ADDITIONALLY, SEA
SURFACE TEMPERATURES AT 28C REMAIN FAVORABLE. HOWEVER, INCREASING
VERTICAL WIND SHEAR (VWS) IS OFFSETTING THESE DYNAMICS. THE CYCLONE
IS TRACKING ALONG THE PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE
(STR) TO THE EAST-NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 18W IS EXPECTED TO TRACK MORE NORTHEASTWARD AND ACCELERATE
AS IT ROUNDS THE WESTERN EDGE OF THE STR AND EMBEDS DEEPER INTO THE
MID-LATITUDE WESTERLIES. THE SYSTEM WILL MAKE LANDFALL OVER KYUSHU,
JAPAN, NEAR TAU 60. INCREASING VWS THEN LAND INTERACTION WILL REDUCE
THE CYCLONE TO 45 KNOTS BY TAU 72.
   C. BEYOND TAU 72, TY MALAKAS WILL DRAG ACROSS THE RUGGED TERRAIN
OF THE JAPANESE ALPS. THIS, IN ADDITION TO STRONG VWS (GREATER THAN
40 KNOTS), WILL CAUSE ITS RAPID DISSIPATION OVER HONSHU. THE NUMERIC
GUIDANCE IS IN TIGHT AGREEMENT WITH SOME DIFFERENCES IN LATERAL
SPEED, LENDING FAIR CONFIDENCE IN THE JTWC TRACK FORECAST.//
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