Tropical Storm MALAKAS Advisory Pzt, 12.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 18W (EIGHTEEN), LOCATED APPROXIMATELY 31
NM SOUTH OF HAGATNA, GUAM, HAS TRACKED WEST-NORTHWESTWARD AT 15
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY AND RADAR IMAGERY INDICATE A CONSOLIDATING LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH IMPROVED CONVECTIVE STRUCTURE. A
111723Z SSMI 85GHZ IMAGE REVEALS MULTIPLE CONVECTIVE BANDS WRAPPING
INTO AN ELONGATED, WELL-DEFINED CENTER. THE MOST RECENT SURFACE
OBSERVATIONS FROM PGUM SHOW SUSTAINED SURFACE WINDS OF 25 TO 30
KNOTS WITH GUSTS UP TO 35 TO 40 KNOTS. THE CURRENT INTENSITY IS
ASSESSED AT 30 KNOTS BASED ON THE IMPROVED CONVECTIVE STRUCTURE AND
SURFACE WIND REPORTS FROM GUAM; THE DVORAK INTENSITY ESTIMATES OF
T1.5 (25 KNOTS) ARE SLIGHTLY LOWER THAN THE CURRENT INTENSITY
ESTIMATE. UPPER-LEVEL ANALYSIS DEPICTS A VERY FAVORABLE ENVIRONMENT
WITH AN ENHANCED POLEWARD OUTFLOW CHANNEL ASSOCIATED WITH A BROAD
TUTT CELL TO THE NNE AND LOW VERTICAL WIND SHEAR. TD 18W IS TRACKING
ALONG THE SOUTHERN PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE
(STR) ENTRENCHED TO THE NORTH.
3. FORECAST REASONING.
   A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE FOR 18W AND
SETS THE FORECAST PHILOSOPHY.
   B. TD 18W IS FORECAST TO TRACK WEST-NORTHWESTWARD TO
NORTHWESTWARD THROUGH TAU 72. THE STR IS FORECAST TO ERODE WITH THE
SLOW APPROACH OF A MAJOR SHORTWAVE TROUGH (CURRENTLY OVER EASTERN
CHINA AND IMPACTING THE FORECAST TRACK OF TY 16W). THIS FORECAST
SCENARIO IS CONSISTENT WITH THAT OF TY 16W AS BOTH SYSTEMS WILL BE
AFFECTED BY THE MAJOR SHORTWAVE TROUGH AS IT PROGRESSES EASTWARD.
DYNAMIC GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72 WITH A 100-NM
SPREAD IN SOLUTIONS AT TAU 72. TD 18W IS FORECAST TO INTENSIFY
RAPIDLY OVER THE NEXT TWO TO THREE DAYS DUE TO THE ROBUST POLEWARD
OUTFLOW ASSOCIATED WITH THE AFOREMENTIONED TUTT CELL, WHICH IS
EXPECTED TO TRACK WESTWARD WITH THE SYSTEM. CONSEQUENTLY, PEAK
INTENSITY SHOULD BE NEAR 115 KNOTS (OR HIGHER) BY TAU 72.
   C. AFTER TAU 72, TD 18W IS FORECAST TO TRACK POLEWARD TOWARD
OKINAWA ALONG THE WESTERN PERIPHERY OF THE POLEWARD-ORIENTED STR.
DYNAMIC GUIDANCE DIVERGES WITH A SPREAD OF 300-NM IN SOLUTIONS AT
TAU 120. DYNAMIC GUIDANCE INDICATES INCREASING UNCERTAINTY WITH
MODEL SOLUTIONS JUST EAST OF ISHIGAKI-JIMA TO JUST EAST OF OKINAWA;
THESE SOLUTIONS ARE ALL VIABLE CONSIDERING THE COMPLEX TIMING OF THE
MAJOR SHORTWAVE TROUGH OVER EASTERN CHINA AND THE EAST CHINA SEA. TD
18W SHOULD WEAKEN GRADUALLY AS IT INTERACTS WITH THE TROUGH.
OVERALL, THERE IS LOW CONFIDENCE (LARGE MODEL SPREAD) IN THE JTWC
FORECAST, PARTICULARLY AFTER TAU 72.//
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