Tropical Storm NANGKA Advisory pt., 10.07.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 11W (NANGKA) WARNING NR
27//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 11W (NANGKA), LOCATED APPROXIMATELY 398 NM
SOUTH-SOUTHEAST OF IWO TO, HAS TRACKED WESTWARD AT 09 KNOTS OVER THE
PAST SIX HOURS. RECENT MSI CONTINUES TO SHOW A COMPACT DEEP
CONVECTIVE CORE WITH A DISTINCT 11-NM DIAMETER EYE. THE CURRENT
POSITION IS BASED ON THE EYE FEATURE WITH HIGH CONFIDENCE. THE
INITIAL INTENSITY OF 130 KNOTS BASED ON AN OVERALL ASSESSMENT OF
DVORAK INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES. UPPER-LEVEL
ANALYSIS INDICATES NANGKA IS LOCATED IN AN AREA OF MODERATE VWS AND
GOOD DIVERGENT OUTFLOW WITH AN EQUATORWARD BIAS. STY 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. STY 11W WILL CONTINUE TO TRACK WEST-NORTHWESTWARD THROUGH TAU
36 UNDER THE DOMINANT STEERING STR. MARGINAL CONDITIONS ARE EXPECTED
TO BEGIN ITS WEAKENING TREND. NEAR TAU 36, STY NANGKA WILL SLOW AND
BEGIN TO TURN POLEWARD TOWARDS A BREAK IN THE STEERING STR CAUSED BY
A MID-LATITUDE TROUGH PASSING TO THE NORTH. VWS WILL FURTHER
INCREASE DUE TO A TIGHTENED PRESSURE GRADIENT BETWEEN THE
AFOREMENTIONED TROUGH AND A RIDGE BUILDING TO ITS WEST, FORCING
STRONG NORTHERLY FLOW ALOFT.
   C. IN THE EXTENDED TAUS, STY 11W WILL TURN NORTHWESTWARD AGAIN AS
A MID-LATITUDE RIDGE STRENGTHENS THE STEERING STR ALLOWING IT TO
BUILD BACK OVER THE SYSTEM. HIGH VWS AND REDUCED OUTFLOW ALOFT WILL
PERSIST THROUGH TAU 96. BEYOND TAU 96, THE UPPER LEVEL FLOW WILL
BECOME IN-PHASE WITH THE CYCLONE, REDUCING THE VWS IMPACTS AND
ALLOWING STY 11W TO RE-INTENSIFY THROUGH THE END OF THE FORECAST
PERIOD. DYNAMIC MODEL GUIDANCE REMAINS GOOD AGREEMENT THROUGH TAU
72. DUE TO THE CONTINUED SPREAD IN THE MODEL SOLUTIONS AFTER 72
HOURS BECAUSE OF THEIR DEPICTION OF THE APPROACHING MID-LATITUDE
TROUGH, THE JTWC TRACK FORECAST CONFIDENCE LEVEL REMAINS LOW.//
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