Tropical Storm KROVANH Advisory Sun Sep 20

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KROVANH) WARNING NR 19//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 20W (KROVANH), LOCATED APPROXIMATELY 444 NM SOUTH-
SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD AT 15 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) CONTINUES TO SHOW CURVED CONVECTIVE BANDING WRAPPING TIGHTLY
INTO THE CENTER. THE CURRENT POSITION IS BASED ON THE MSI, MICROWAVE
EYE FEATURE ON 190545Z IMAGE AND SATELLITE FIXES FROM PGTW AND RJTD
WITH HIGH CONFIDENCE. THE INITIAL INTENSITY REMAINS AT 75 KNOTS
BASED ON DVORAK CURRENT INTENSITY ESTIMATES OF T4.5 (77 KNOTS) FROM
ALL REPORTING AGENCIES. UPPER-LEVEL ANALYSIS SHOWS A MARGINALLY-
FAVORABLE ENVIRONMENT WITH STRONG SOUTHWESTERLY VERTICAL WIND SHEAR
OFFSET BY VIGOROUS POLEWARD OUTFLOW. TY 20W IS TRACKING ALONG THE
NORTHWESTERN PERIPHERY OF A DEEP-LAYERED STR.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 20W WILL REMAIN ON A NORTHEASTWARD TRAJECTORY THROUGH THE
REMAINDER OF THE FORECAST PERIOD. THE COMBINED EFFECT OF INCREASING
VWS AND COOLER SST WILL FURTHER WEAKEN KROVANH. THE SYSTEM WILL
BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY TAU 48 AS IT BECOMES
EMBEDDED WITHIN THE MIDLATITUDE WESTERLIES AND SHOULD COMPLETE ETT
BY TAU 72 AS IT GAINS FRONTAL CHARACTERISTICS. DYNAMIC GUIDANCE IS
IN GOOD AGREEMENT THROUGH TAU 48. AFTER TAU 48, DYNAMIC GUIDANCE
DIVERGES DUE TO AN ATYPICAL SYNOPTIC PATTERN, WHICH WILL SERVE TO
WEAKEN THE MIDLATITUDE WESTERLIES, PRODUCING A SLOWER RE-CURVE
SCENARIO. OVERALL, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST
TRACK WHICH IS POSITIONED CLOSE TO MULTI-MODEL CONCENSUS.//
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