Tropical Storm NANGKA Advisory Fri Jul 10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR
29//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 11W (NANGKA), LOCATED APPROXIMATELY 890 NM EAST-
SOUTHEAST OF KADENA AB, HAS TRACKED WESTWARD AT 08 KNOTS OVER THE
PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY DEPICTS A
WEAKENING SYSTEM WITH A CLOUD-FILLED EYE AND SPIRAL BANDING LOCATED
PRIMARILY OVER THE SOUTHERN SEMI-CIRCLE DUE TO INCREASING NORTHERLY
VERTICAL WIND SHEAR (VWS). A 101157Z METOP-B 89 GHZ IMAGE ALSO SHOWS
THE DECAYING CONVECTIVE STRUCTURE WITH AN ERODING EYEWALL OVER THE
NORTHERN QUADRANT. BASED ON THE EYE, 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 110 KNOTS BASED ON DECREASING DVORAK INTENSITY
ESTIMATES OF T5.0/6.0 FROM PGTW. 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 WESTWARD TO WEST-NORTHWESTWARD
THROUGH TAU 24 UNDER THE DOMINANT STEERING STR. MARGINALLY-FAVORABLE
UPPER-LEVEL CONDITIONS ARE EXPECTED TO CONTINUE, LEADING TO A
MARKED, STEADY WEAKENING TREND THROUGH TAU 72. AFTER TAU 24, TY
NANGKA WILL SLOW AND BEGIN TO TURN POLEWARD ALONG THE WESTERN
PERIPHERY OF A RE-ORIENTING STR. DYNAMIC GUIDANCE IS IN BETTER
AGREEMENT, HOWEVER, THERE REMAINS SIGNIFICANT UNCERTAINTY IN THE
TIMING AND DEGREE OF THE POLEWARD TRACK CHANGE.
   C. IN THE EXTENDED TAUS, TY 11W WILL TURN NORTHWESTWARD TOWARD
THE RYUKYU ISLANDS 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 IS IN FAIR AGREEMENT WITH
ALL MODELS NOW SHOWING A TRACK TOWARD THE RYUKYU ISLANDS. DUE TO THE
LARGE SPREAD OF ABOUT 300 NM IN THE MODEL SOLUTIONS AT TAU 120, THE
JTWC TRACK FORECAST CONFIDENCE LEVEL REMAINS LOW.//
NNNN
NNNN