Tropical Storm MALAKAS Advisory 18 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (MALAKAS) WARNING NR 25//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 18W (MALAKAS), LOCATED APPROXIMATELY 93 NM NORTHEAST OF
TAIPEI, TAIWAN, HAS TRACKED NORTHWARD AT 02 KNOTS OVER THE PAST SIX
HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS WARMING
CONVECTIVE CLOUD TOPS, AND A BROADENING CIRCULATION OVER THE PAST 12
HOURS INDICATING THE SYSTEM HAS WEAKENED. A 171908Z AMSU 89 GHZ
IMAGE ALSO REVEALS A DECREASE IN DEEP CONVECTION ALONG THE WESTERN
SEMICIRCLE WHERE DRY AIR IS BEGINNING TO IMPINGE ON THE SYSTEM. THE
CURRENT BEST TRACK POSITION IS SUPPORTED BY THE AFOREMENTIONED
IMAGERY WITH GOOD CONFIDENCE. THE INITIAL INTENSITY OF 85 KNOTS IS
BASED ON AN OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK
ESTIMATES AND REFLECTS THE WEAKENED STATE. UPPER-LEVEL ANALYSIS
INDICATES A MARGINALLY FAVORABLE ENVIRONMENT WITH GOOD OUTFLOW
OFFSET BY MODERATE (15 TO 20 KNOTS) VERTICAL WIND SHEAR (VWS). SEA
SURFACE TEMPERATURES REMAIN FAVORABLE (AROUND 28C), HOWEVER OCEAN
HEAT CONTENT VALUES REMAINS UNFAVORABLE FOR DEVELOPMENT. THE CYCLONE
IS TRACKING ALONG THE WESTERN 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 BEGIN TRACKING ON A MORE NORTHEASTWARD
TRAJECTORY AND ACCELERATE AS IT ROUNDS THE WESTERN PERIPHERY OF THE
STR AND EMBEDS DEEPER INTO THE STRONG MID-LATITUDE WESTERLIES. THIS
SYSTEM IS FORECAST TO WEAKEN GRADUALLY THROUGH THE FIRST 48 HOURS AS
VWS SLOWLY INCREASES. THE SYSTEM WILL MAKE LANDFALL OVER KYUSHU,
JAPAN, JUST AFTER TAU 48.
   C. BEYOND TAU 72, TY MALAKAS WILL THE SYSTEM WILL CONTINUE
ACCELERATING NORTHEASTWARD ALONG COASTAL JAPAN WITHIN THE
WESTERLIES. VWS WILL BECOME INCREASINGLY UNFAVORABLE, RESULTING IN
RAPID WEAKENING OF THE SYSTEM. TC 18W IS FORECAST TO FULLY DISSIPATE
BY TAU 96, JUST OFFSHORE OF TOKYO. DYNAMIC MODEL GUIDANCE IS IN GOOD
AGREEMENT ON THE FORECAST TRACK, HOWEVER THERE ARE SOME DIFFERENCES
IN THE SPEED OF MOVEMENT OF TY MALAKAS, ESPECIALLY AFTER TAU 48.
THEREFORE, THERE IS FAIR CONFIDENCE IN THE JTWC TRACK FORECAST.//
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