Tropical Storm CHOI-WAN Advisory Tue Oct 06

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (CHOI-WAN) WARNING
NR 12//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 23W (CHOI-WAN), LOCATED APPROXIMATELY 703 NM
NORTHEAST OF ANDERSEN AFB, GUAM HAS TRACKED WESTWARD AT 09
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS TIGHTLY-CURVED BANDING WRAPPING INTO A MORE
CONSOLIDATED LOW LEVEL CIRCULATION CENTER (LLCC) WITH AN IMPROVEMENT
IN THE OVERALL CONVECTIVE STRUCTURE. A 050535Z SSMIS 37GHZ MICROWAVE
IMAGE FURTHER ILLUSTRATES THE INCREASED CONSOLIDATION OF THE LLCC
WITH DEEP CONVECTION NOW WRAPPING AROUND THE LLCC WHICH PROVIDES
GOOD CONFIDENCE IN THE INITIAL POSITION. THE CURRENT INTENSITY HAS
BEEN INCREASED TO 60 KNOTS, SLIGHTLY HIGHER THAN DVORAK INTENSITY
ESTIMATES RANGING FROM 45 TO 55 KNOTS, DUE TO THE SIGNIFICANT
IMPROVEMENT IN THE STORM STRUCTURE AND AN INCREASING TREND IN THE
SATCON INTENSITY ESTIMATES. UPPER-LEVEL ANALYSIS CONTINUES TO SHOW A
FAVORABLE ENVIRONMENT WITH RADIAL OUTFLOW AND LOW VERTICAL WIND
SHEAR (VWS). ADDITIONALLY, WARM SEA SURFACE TEMPERATURES (SSTS) ARE
CONDUCIVE FOR FURTHER DEVELOPMENT. TS 23W IS TRACKING ALONG THE
SOUTHERN PERIPHERY OF A DEEP-LAYERED SUB-TROPICAL RIDGE (STR) TO THE
NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. TS 23W WILL CONTINUE TRACKING WESTWARD UNDER THE INFLUENCE OF
THE STR OVER THE NEXT 12 HOURS. AFTERWARDS, TS CHOI-WAN WILL ROUND
THE SOUTHWESTERN PERIPHERY OF THE STEERING STR AND TRACK MORE
POLEWARD. FAVORABLE ENVIRONMENTAL CONDITIONS WILL PERSIST FOR THE
NEXT 36 HOURS, ALLOWING TS 23W TO REACH TYPHOON INTENSITY BEFORE
MOVING INTO AN UNFAVORABLE ENVIRONMENT. HOWEVER, DUE TO THE BROAD
NATURE OF THE SYSTEM, THE RATE OF INTENSIFICATION WILL BE HAMPERED
WHILE IT FULLY CONSOLIDATES. BEYOND TAU 36, THE STORM WILL BEGIN TO
INTERACT WITH THE BAROCLINIC ZONE WHERE VWS WILL INCREASE ABOVE 30
KNOTS. IN ADDITION, DECREASING SSTS WILL FURTHER WEAKEN THE SYSTEM.
NEAR TAU 48, TS 23W WILL BECOME ENGULFED BY A MID-LATITUDE TROUGH
WHICH WILL FURTHER INCREASE THE VWS AND BEGIN EXTRA-TROPICAL
TRANSITION (ETT).
   C. IN THE EXTENDED FORECAST, TS CHOI-WAN WILL CONTINUE ETT AS IT
EMBEDS DEEPER INTO THE MID-LATITUDE WESTERLIES AND GAINS FRONTAL
CHARACTERISTICS. TS 23W WILL COMPLETE ETT BY THE END OF THE FORECAST
PERIOD AS A STRONG COLD-CORE LOW. DYNAMIC MODEL GUIDANCE IS NOW IN
VERY TIGHT AGREEMENT THROUGHOUT THE FORECAST PERIOD. WITH THE
INCREASED CONSOLIDATION SEEN IN THE AFOREMENTIONED IMAGERY AND THE
TIGHT AGREEMENT AMONG MODEL GUIDANCE, THERE IS NOW HIGH CONFIDENCE
IN THE JTWC TRACK FORECAST.//
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