Tropical Storm NANGKA Advisory Tue Jul 07

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR 15//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 11W (NANGKA), LOCATED APPROXIMATELY 585 NM EAST-SOUTHEAST
OF SAIPAN, HAS TRACKED WEST-NORTHWESTWARD AT 11 KNOTS OVER THE
PAST SIX HOURS. RECENT ANIMATED MULTISPECTRAL SATELLITE IMAGERY
DEPICTS A WELL DEVELOPED SYSTEM WITH A 15 NM EYE AND ROBUST OUTFLOW.
A 062044Z SSMIS MICROWAVE IMAGE REVEALS A SOLID EYEWALL WITH
FORMATIVE CONVECTIVE BANDS WRAPPING INTO THE SYSTEM. THE INITIAL
POSITION IS BASED ON THE MSI ANIMATION AND AFOREMENTIONED MICROWAVE
IMAGE WITH HIGH CONFIDENCE. THE INTENSITY HAS BEEN ASSESSED AT 95
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 72 HOURS WITH NANGKA FORECASTED
TO PEAK AT 130 KNOTS BY TAU 48 AND MAINTAIN 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 WEAK STEERING ENVIRONMENT AND ALLOWING THE SYSTEM TO
BEGIN MOVING POLEWARD. ALTHOUGH NANGKA WILL HAVE GOOD POLEWARD
OUTFLOW, SSTS AND OHC VALUES DECREASE POLEWARD OF 19N AND VWS
SHEAR WILL BEGIN TO INCREASE AS WELL. DYNAMIC MODEL GUIDANCE HAS
COME INTO TIGHTER AGREEMENT CONCERNING THE TIMING AND OVERALL EFFECT
OF THE MID-LATITUDE TROUGH BREAKING DOWN THE STR IN THE EXTENDED
TAUS. COMBINED WITH THE CLOSE AGREEMENT IN THE GUIDANCE THROUGH TAU
72, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST WHICH IS LAID
CLOSE TO THE MULTI-MODEL CONSENSUS AND HEDGED SLIGHTLY CLOSER TO THE
GFS AND ECMWF SOLUTIONS.//
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