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WDPN33 PGTW 200900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (MALAKAS) WARNING
NR 35//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM (TS) 18W (MALAKAS), LOCATED APPROXIMATELY 187 NM
WEST-SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD AT 25
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY AND RADAR IMAGERY DEPICT A RAPIDLY WEAKENING LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH DEEP CONVECTION SHEARED OVER THE
NORTHEAST QUADRANT OF THE LLCC. A 200625Z SSMIS 91GHZ IMAGE SHOWS AN
EXPOSED CENTER DISPLACED JUST SOUTHWEST OF THE DEEP CONVECTION; THIS
POSITION COINCIDES WELL WITH THE 200600Z JMA RADAR FIX POSITION AND
THE CURRENT WARNING POSITION WITH HIGH CONFIDENCE.
AT 20/0400Z TS
18W MADE LANDFALL OVER HONSHU ABOUT 13NM NORTHWEST OF NANKI-
SHIRAHAMA AIRPORT, WHICH REPORTED MAXIMUM SURFACE WINDS OF ABOUT 50
KNOTS. ADDITIONAL SURFACE OBSERVATIONS FROM THE COASTAL CITY OF
SHIONOMISAKI (33.4N 135.8E) INDICATED MAXIMUM WINDS OF 46 KNOTS.
CONSEQUENTLY, THE CURRENT INTENSITY IS ASSESSED AT 55 KNOTS BASED
PRIMARILY ON THE DECAYING CONVECTIVE STRUCTURE AND SURFACE
OBSERVATIONS. UPPER-LEVEL ANALYSIS INDICATES A HOSTILE ENVIRONMENT
CHARACTERIZED BY STRONG (40 TO 50 KNOTS) VERTICAL WIND SHEAR (VWS).
CURRENTLY TS 18W IS ACCELERATING NORTHEASTWARD ALONG THE
NORTHWESTERN PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE, WITHIN
THE MIDLATITUDE WESTERLIES.
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
B. TS 18W IS FORECAST TO TRACK RAPIDLY NORTHEASTWARD TO EAST-
NORTHEASTWARD THROUGH THE FORECAST PERIOD. DYNAMIC MODEL GUIDANCE IS
IN EXCELLENT AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THE
JTWC FORECAST TRACK. THE SYSTEM WILL CONTINUE TO WEAKEN RAPIDLY DUE
TO LAND INTERACTION, PERSISTENT STRONG VWS AND COOLER SST, AND IS
EXPECTED TO DISSIPATE BY TAU 36.//
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