Tropical Storm MALAKAS Advisory Wed Sep 14

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (MALAKAS) WARNING
NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 18W (MALAKAS), LOCATED APPROXIMATELY 310 NM
NORTH-NORTHWEST OF YAP, HAS TRACKED WESTWARD AT 10 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THE
SYSTEM CONTINUES TO STRUGGLE AS DEVELOPMENT IS HINDERED BY SUBSIDENCE
ALONG THE NORTHERN PERIPHERY CAUSED BY THE OUTFLOW EMANATING FROM STY
16W (MERANTI). THE INITIAL POSITION IS BASED ON A LOW REFLECTIVITY
CIRCULATION FEATURE IN THE 130538Z AMSU-B MICROWAVE SATELLITE PASS
WITH FAIR CONFIDENCE. THE INITIAL INTENSITY OF 45 KNOTS IS BASED ON
ACCORDANT DVORAK ESTIMATES FROM PGTW AND RJTD. ENVIRONMENTAL ANALYSIS
REVEALS A MARGINAL ENVIRONMENT DUE TO THE NEGATIVE IMPACTS OF THE
OUTFLOW FROM STY 16W EXACERBATED BY MODERATE (15-20 KNOT) VERTICAL
WIND SHEAR (VWS) HOWEVER, WATER VAPOR IMAGERY SHOWS A TUTT CELL
LOCATED TO THE NORTHEAST PRODUCING ENHANCED EASTERLY OUTFLOW WHICH IS
PROVIDING SUFFICIENT VENTILATION FOR THE CENTRAL CONVECTION. SEA
SURFACE TEMPERATURES (SSTS) REMAIN FAVORABLE NEAR 29 CELSIUS. TS 18W
IS TRACKING ALONG THE SOUTHERN PERIPHERY OF THE DEEP-LAYERED
SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 18W IS FORECAST TO TRACK WEST-NORTHWESTWARD THEN
NORTHWESTWARD THROUGH TAU 72. TS MALAKAS WILL INTENSIFY OVER THE NEXT
12 HOURS, BUT AT A SLOW RATE, DUE TO THE NEGATIVE DYNAMICS MENTIONED
IN PARA 2. HOWEVER, BY TAU 24, AS DISTANCE BETWEEN THE CYCLONES
INCREASE, THE VWS WILL DECREASE AND THE OUTFLOW WILL IMPROVE,
ALLOWING A RAPID RATE OF INTENSIFICATION, PEAKING AT 115 KNOTS BY TAU
72.
   C. IN THE EXTENDED FORECAST, TS 18W WILL REACH THE WESTERN EXTENT
OF THE STEERING STR AND TURN POLEWARD INTO THE STRONG MID-LATITUDE
WESTERLIES. STRONG VWS WILL GRADUALLY WEAKEN THE CYCLONE AS IT
ACCELERATES NORTHEASTWARD. DYNAMIC MODEL GUIDANCE IS IN BETTER
AGREEMENT. THERE IS OVERALL FAIR CONFIDENCE IN THE JTWC TRACK
FORECAST.//
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