Saturday, September 3, 2011

JTWC - Prognostic Reasoning for Tropical Cyclone Advisory 36 - Tropical Storm Talas

WDPN32 PGTW 030300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W WARNING NR 36//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
A. TROPICAL STORM 15W (TALAS), LOCATED APPROXIMATELY 100 NM EAST-
SOUTHEAST OF IWAKUNI, JAPAN, HAS TRACKED JUST WEST OF NORTHWARD
AT 05 KNOTS AND MOVED INLAND OVER EASTERN SHIKOKU. ANIMATED INFRARED
SATELLITE IMAGERY SHOWS THE CONVECTIVE BANDS HAVE BECOME FRAGMENTED
AS CLOUDS TOPS WARMED UP. THE INITIAL POSITION WAS BASED ON A RADAR
REFLECTIVITY LOOP FROM SHIKOKU WITH FAIR CONFIDENCE. THE INITIAL
INTENSITY WAS BASED ON NEARBY LAND AND SHIP OBSERVATIONS AND
SUPPORTED BY DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD. UPPER LEVEL
ANALYSIS INDICATES THE STORM IS JUST TO THE NORTH OF THE RIDGE AXIS
IN AN AREA OF MODERATE (15-20 KT) VERTICAL WIND SHEAR (VWS). TS 15W
IS TRACKING ALONG THE WESTERN EDGE OF A DEEP-LAYERED SUBTROPICAL
RIDGE TO THE EAST.
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST PHILOSOPHY.
B. A MID-LATITUDE TROUGH IS APPROACHING FROM THE NORTHWEST AND IS
EXPECTED TO WEAKEN THE AFOREMENTIONED STEERING RIDGE AND CAUSE TS
TALAS TO RECURVE TO THE NORTHEAST AS IT MOVES INTO THE SEA OF JAPAN
(SOJ) AFTER TAU 12. THE SYSTEM WILL THEN RAPIDLY ABSORB INTO THE
BAROCLINIC ZONE, BECOMING AN EXTRA-TROPICAL SYSTEM BEFORE TAU 36.
THE INCREASED VWS AND COOLING SEA SURFACE TEMPERATURES IN THE SOJ
WILL ALSO RAPIDLY WEAKEN THE SYSTEM INTO A 30-KT LOW BY TAU 36. THE
AVAILABLE NUMERICAL GUIDANCE ARE MOSTLY UNRELIABLE. WITH THE
EXCEPTION OF ECMWF, ALL MODELS ARE BRINGING THE VORTEX DUE NORTH
TOWARDS THE RUSSIAN FAR EAST AND INTO THE JET STREAM - AN UNLIKELY
SCENARIO. THIS TRACK FORECAST IS MORE IN LINE WITH ECMWF, RECURVING
THE CYCLONE NORTHEASTWARD.//

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