Tropical Storm NANGKA Advisory Fri Jul 10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR 24//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 11W (NANGKA), LOCATED APPROXIMATELY 144 NM NORTH OF
SAIPAN, HAS TRACKED WEST-NORTHWESTWARD AT 11 KNOTS OVER THE PAST
SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS TIGHT
SPIRAL BANDING WRAPPING INTO A COMPACT AND INTENSE CONVECTIVE CORE
STRUCTURE THAT IS SURROUNDING A SHARP 20-NM EYE. THIS SUPPORTS THE
INITIAL POSITION WITH HIGH CONFIDENCE. A 090446Z SSMI 85GHZ
MICROWAVE IMAGE SHOWS A MOSTLY SYMMETRIC SYSTEM WITH THE MOST
INTENSE CONVECTION WITHIN THE SPIRAL BANDING AND ALONG THE NORTHERN
EYEWALL. THE INITIAL INTENSITY REMAINS AT 125 KNOTS BASED ON AN
ASSESSMENT OF DVORAK INTENSITY ESTIMATES AND NO SIGNIFICANT CHANGE
OVER THE PAST SIX HOURS IN THE BD CURVE ENHANCEMENT. UPPER LEVEL
ANALYSIS INDICATES A MOSTLY FAVORABLE ENVIRONMENT WITH LOW TO
MODERATE (10-20 KNOTS) NORTHWESTERLY VERTICAL WIND SHEAR (VWS) AND
GOOD DIVERGENT OUTFLOW. HOWEVER, THE TUTT CELL PREVIOUSLY LOCATED TO
THE NORTHWEST HAS MOSTLY DISSIPATED AND IS NO LONGER ENHANCING THE
POLEWARD OUTFLOW CHANNEL, WHICH IS EVIDENT IN WATER VAPOR IMAGERY.
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
48 UNDER THE DOMINANT STEERING STR. ENVIRONMENTAL CONDITIONS ARE
EXPECTED TO REMAIN MOSTLY UNCHANGED OVER THE NEXT 12 HOURS, ALLOWING
TY 11W TO SLIGHTLY INTENSIFY TO SUPER TYPHOON INTENSITY. BEYOND TAU
12, ENVIRONMENTAL CONDITIONS WILL BEGIN TO DETERIORATE AS TY NANGKA
MOVES INTO A MODERATE TO HIGH VWS ENVIRONMENT AND REDUCED POLEWARD
OUTFLOW. NEAR TAU 48, TY NANGKA WILL SLOW AND BEGIN TO TURN POLEWARD
TOWARDS A BREAK IN THE STEERING STR CAUSED BY A FAST MOVING MID-
LATITUDE TROUGH APPROACHING FROM THE WEST.
   C. IN THE EXTENDED TAUS, TY 11W WILL TURN NORTHWESTWARD AGAIN AS
A MID-LATITUDE RIDGE STRENGTHENS THE STEERING STR ALLOWING IT TO
BUILD BACK OVER THE SYSTEM. THE BUILDING RIDGE AHEAD OF THE SYSTEM
WILL HAMPER OUTFLOW AND CONTINUE TO INCREASE THE VWS BY THE END OF
THE FORECAST PERIOD. WITH THE EXCEPTION OF NAVGEM AND COTC WHICH
CURVES THE SYSTEM INTO THE MID-LATITUDE WESTERLIES, DYNAMIC MODEL
GUIDANCE HAS COME INTO BETTER AGREEMENT BEYOND TAU 72 WITH THE
WESTWARD COMPONENT TO THE TRACK. HOWEVER, DUE TO THE CONTINUED
SPREAD IN THE MODEL SOLUTIONS AFTER 72 HOURS AND THEIR DEPICTION OF
THE APPROACHING TROUGH, THERE IS LOW CONFIDENCE IN THE JTWC
FORECAST.//
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