Tropical Storm KROVANH Advisory Thu Sep 17

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (KROVANH) WARNING
NR 07//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 20W (KROVANH), LOCATED APPROXIMATELY 391 NM
NORTH-NORTHEAST OF ANDERSEN AFB, GUAM, HAS TRACKED WEST-
NORTHWESTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. ANIMATED MSI
CONTINUES TO SHOW DEEPENED CONVECTION WITH TIGHTLY-CURVED BANDING
WRAPPING INTO THE CENTER. THE CURRENT POSITION IS BASED ON THE MSI
AND CORRESPONDING FIXES FROM PGTW AND RJTD WITH HIGH CONFIDENCE. THE
INITIAL INTENSITY OF 55 KNOTS IS BASED ON THE IMPROVED STRUCTURE AND
DVORAK INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES. UPPER-LEVEL
ANALYSIS INDICATES KROVANH IS LOCATED IN A FAVORABLE ENVIRONMENT
WITH LOW VWS AND GOOD DUAL OUTFLOW. ADDITIONALLY, WARM SSTS IN THE
AREA ARE CONDUCIVE FOR THE INTENSIFICATION. TS 20W CONTINUES TO
TRACK ALONG THE PERIPHERY OF A SUBTROPICAL STEERING RIDGE TO THE
NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 20W IS EXPECTED TO TRACK GENERALLY NORTHWESTWARD ALONG THE
PERIPHERY OF THE CURRENT STEERING RIDGE FOR THE NEXT 36 HOURS BEFORE
TURNING POLEWARD AND ROUNDING THE RIDGE AXIS THROUGH TAU 72.
CONTINUED FAVORABLE ENVIRONMENTAL AND UPPER-LEVEL CONDITIONS WILL
ALLOW THE SYSTEM TO UNDERGO RAPID INTENSIFICATION, LEADING TO A PEAK
INTENSITY OF 115 KNOTS BY TAU 48.
   C. IN THE EXTENDED TAUS, TS 20W WILL REMAIN ON THE NORTHEASTWARD
TRAJECTORY. INCREASING VWS AND COOLER SSTS WILL BEGIN WEAKEN THE
SYSTEM AS IT ACCELERATES INTO THE MIDLATITUDE BAROCLINIC ZONE.
DYNAMIC MODEL GUIDANCE IS OVERALL IN GOOD AGREEMENT LENDING TO HIGH
CONFIDENCE IN THE JTWC TRACK FORECAST WHICH IS POSITIONED CLOSE TO
MULTI-MODEL CONSENSUS.//
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