Tropical Storm NANGKA Advisory Sa, 07.07.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR 14//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 11W (NANGKA), LOCATED APPROXIMATELY 652 NM EAST-SOUTHEAST
OF SAIPAN, HAS TRACKED WEST-NORTHWESTWARD AT 11 KNOTS OVER THE
PAST SIX HOURS. RECENT ANIMATED ENHANCED SATELLITE INFRARED IMAGERY
DEPICTS A WELL DEVELOPED SYSTEM WITH A 10 NM EYE AND ROBUST OUTFLOW.
A 061806Z GPM MICROWAVE IMAGE REVEALS THE STRUCTURE OF THE EYEWALL
HAS IMPROVED OVER THE PAST 6 HOURS AS IT IS SMALLER AND LESS RAGGED.
THE INITIAL POSITION IS BASED ON THE EIR ANIMATION AND
AFOREMENTIONED MICROWAVE IMAGE WITH HIGH CONFIDENCE. THE INTENSITY
HAS BEEN ASSESSED AT 85 KNOTS BASED ON AN AVERAGE OF DVORAK
INTENSITY ESTIMATES FROM PGTW AND RJTD. UPPER LEVEL ANALYSIS
INDICATES AN ENVIRONMENT CHARACTERIZED BY RADIAL OUTFLOW AND 10-20
KNOT NORTHWESTERLY VERTICAL WIND SHEAR. TY 11W IS CURRENTLY TRACKING
ALONG THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE TO THE
NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 11W WILL CONTINUE TRACKING TO THE NORTHWEST UNDER THE
EXTENSION OF THE STR THROUGH TAU 72. THE UPPER LEVEL ENVIRONMENT
WILL REMAIN FAVORABLE OVER THE NEXT 48 HOURS WITH TY NANGKA PEAKING
AT 115 KNOTS BY TAU 48 AND MAINTAINING THROUGH TAU 72.
   C. IN THE EXTENDED TAUS TY 11W WILL BEGIN TO SLOW AS AN
APPROACHING MID-LATITUDE TROUGH WEAKENS THE EXTENSION OF THE STR
CREATING A WEAKER STEERING ENVIRONMENT AND ALLOWING THE SYSTEM TO
BEGIN MOVING POLEWARD. ALTHOUGH NANGKA WILL HAVE GOOD POLEWARD
OUTFLOW, SSTS AND OHC VALUES DECREASE POLEWARD OF 19 NORTH AND VWS
SHEAR WILL BEGIN TO INCREASE AS WELL. AFTER TAU 72, DYNAMIC MODEL
GUIDANCE IS IN DISAGREEMENT WITH THE TIMING AND OVERALL EFFECT OF
THE MID-LATITUDE TROUGH BREAKING DOWN THE STR RESULTING IN
UNCERTAINTY IN THE EXTENDED TAUS. HOWEVER, THE MODEL GUIDANCE IS IN
VERY GOOD AGREEMENT THROUGH TAU 72 LENDING HIGH CONFIDENCE TO THE
JTWC FORECAST WHICH IS LAID CLOSE TO THE MULTI-MODEL CONSENSUS.//
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