Tropical Storm NANGKA Advisory Sat Jul 11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR
28//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 11W (NANGKA), LOCATED APPROXIMATELY 386 NM SOUTH OF
IWO TO, HAS TRACKED WESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS.
ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A COMPACT SYSTEM
WITH A 9-NM ROUND EYE AND SPIRAL BANDING OVER THE SOUTHERN SEMI-
CIRCLE. A 100448Z NOAA-19 89 GHZ IMAGE INDICATES A SLIGHT WEAKENING
TREND WITH DECAYING DEEP CONVECTION OVER THE NORTHERN SEMI-CIRCLE,
HOWEVER, THERE IS HIGH CONFIDENCE IN THE CURRENT POSITION. ANIMATED
WATER VAPOR IMAGERY DEPICTS GOOD EQUATORWARD OUTFLOW, HOWEVER,
INCREASING NORTHERLY FLOW AND INCREASED VWS IS HAMPERING CONVECTIVE
DEVELOPMENT OVER THE NORTHERN SEMI-CIRCLE. THEREFORE, THE CURRENT
INTENSITY IS NOW ASSESSED SLIGHTLY LOWER AT 125 KNOTS BASED ON
DECREASING DVORAK INTENSITY ESTIMATES. TY NANGKA IS TRACKING ALONG
THE SOUTHERN PERIPHERY OF AN EXTENSION OF THE DEEP LAYERED SUB-
TROPICAL RIDGE (STR) TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 11W WILL CONTINUE TO TRACK WEST-NORTHWESTWARD THROUGH TAU
36 UNDER THE DOMINANT STEERING STR. MARGINALLY-FAVORABLE UPPER-LEVEL
CONDITIONS ARE EXPECTED TO CONTINUE, LEADING TO A MARKED, STEADY
WEAKENING TREND THROUGH TAU 72. NEAR TAU 36, TY NANGKA WILL SLOW AND
BEGIN TO TURN POLEWARD ALONG THE WESTERN PERIPHERY OF A RE-ORIENTING
STR. DYNAMIC GUIDANCE REMAINS IN FAIR AGREEMENT WITH SIGNIFICANT
UNCERTAINTY IN THE TIMING AND DEGREE OF THE POLEWARD TRACK CHANGE.
   C. IN THE EXTENDED TAUS, TY 11W WILL TURN NORTHWESTWARD AS THE
STEERING INFLUENCE TRANSITIONS TO THE STR POSITIONED SOUTH OF
MAINLAND JAPAN. VWS IS FORECAST TO DECREASE WITH IMPROVING POLEWARD
OUTFLOW NEAR TAU 120, WHICH WILL ALLOW THE SYSTEM TO RE-INTENSIFY.
DYNAMIC MODEL GUIDANCE DIVERGES AS NAVGEM AND COAMPS-TC TRACK THE
SYSTEM NORTHWARD WHILE THE REMAINDER OF THE GUIDANCE SUPPORTS THE
NORTHWESTWARD TURN. DUE TO THE LARGE SPREAD IN THE MODEL SOLUTIONS
AFTER 72, THE JTWC TRACK FORECAST CONFIDENCE LEVEL REMAINS LOW.//
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