Tropical Storm MALAKAS Advisory Mo, 12.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 02//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 18W (EIGHTEEN), LOCATED APPROXIMATELY 82
NM WEST OF NAVSTA GUAM, HAS TRACKED WEST-NORTHWESTWARD AT 15 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
INDICATES A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC) WITH
RAPIDLY IMPROVING CONVECTIVE STRUCTURE. A 112108Z NOAA-18 89GHZ IMAGE
SHOWS DEEP CONVECTIVE BANDING OVER THE SOUTHERN SEMI-CIRCLE WRAPPING
INTO THE LLCC WITH FRAGMENTED BANDING ELSEWHERE. THE CURRENT
INTENSITY IS ASSESSED AT 30 KNOTS BASED ON A PGTW DVORAK ESTIMATE OF
T2.0, CONSISTENT WITH THE IMPROVED CONVECTIVE STRUCTURE. UPPER-LEVEL
ANALYSIS DEPICTS A VERY FAVORABLE ENVIRONMENT WITH NEAR-RADIAL
OUTFLOW, AND AN ENHANCED POLEWARD OUTFLOW CHANNEL ASSOCIATED WITH A
BROAD TUTT CELL TO THE NNE. TD 18W IS TRACKING ALONG THE SOUTHERN
PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE (STR) ENTRENCHED TO
THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   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 450-NM IN SOLUTIONS AT
TAU 120. DYNAMIC GUIDANCE INDICATES INCREASING UNCERTAINTY WITH
MODEL SOLUTIONS JUST WEST 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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