Tropical Storm KHANUN Advisory Wed Jul 18

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 08W (KHANUN) WARNING
NR 11//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 08W (KHANUN), LOCATED APPROXIMATELY 205 NM SOUTH
OF CHEJU-DO, HAS TRACKED NORTH-NORTHWESTWARD AT 13 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND AN
180037Z SSMIS 85 GHZ IMAGE DEPICT A DEEP CONVECTIVE SPIRAL FEEDER
BAND WRAPPING INTO A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER
(LLCC) FROM THE NORTHERN SEMI-CIRCLE. TS KHANUN'S DEEP CONVECTIVE
STRUCTURE HAS NOT CHANGED OVER THE LAST SIX HOURS. THEREFORE, THE
CURRENT INTENSITY IS MAINTAINED AT 50 KNOTS BASED ON A COMBINATION
OF ANALOGOUS DVORAK ESTIMATES OF 55 KNOTS AND STEADY ADT ESTIMATES
OF 47-51 KNOTS OVER THE PAST 16 HOURS. THE CURRENT POSITION IS
BASED ON THE ABOVE MENTIONED IMAGERY WITH HIGH CONFIDENCE. THE
SYSTEM CONTINUES TO TRACK BETWEEN THE WESTERN PERIPHERY OF A HIGH
AMPLITUDE DEEP LAYER SUBTROPICAL RIDGE (STR) CENTERED SOUTH OF
HONSHU, JAPAN, AND A STATIONARY MID-LATITUDE TROUGH OVER EASTERN
ASIA. UPPER-LEVEL ANALYSIS INDICATES A MARGINAL ENVIRONMENT WITH
WEAK TO MODERATE (10-20 KNOTS) EASTERLY VERTICAL WIND SHEAR.
ANIMATED WATER VAPOR IMAGERY SHOWS GOOD POLEWARD OUTFLOW INTO THE
CREST OF THE HIGHLY AMPLIFIED STR AND EQUATORWARD OUTFLOW HAS BEEN
SQUELCHED BY AN UPPER-LEVEL TROUGH LOCATED EAST OF TAIWAN EXTENDING
EQUATORWARD TO LUZON.
3. FORECAST REASONING.
   A. NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 08W WILL CONTINUE TO TRACK WITHIN THE POLEWARD SYNOPTIC
PATTERN DURING THE REMAINDER OF THE FORECAST PERIOD AND GRADUALLY
WEAKEN. BY TAU 24, TS KHANUN WILL BE SURROUNDED BY COOLER (22-25C)
SEA SURFACE TEMPERATURES AND BEGIN TO PERIPHERALLY INTERACT WITH
THE SOUTHERN KOREAN PENINSULA. THESE UNFAVORABLE CONDITIONS WILL
ONLY INCREASE INTO TAU 36 AS THE LLCC NEARS LANDFALL AND
DISSIPATION OVERLAND IS EXPECTED BY TAU 36. NUMERICAL MODEL
GUIDANCE IS IN GOOD AGREEMENT THROUGH THE FIRST 24 HOURS OF THE
FORECAST PERIOD WITH INCREASING VORTEX TRACKER SPREAD OCCURRING
OVERLAND. THE CURRENT CYCLE GFS AND ECMWF TRACK THE VORTEX TOWARDS
A LOW-LEVEL MID-LATITUDE CIRCULATION, AND ASSOCIATED VORTICITY,
FORMING OFF THE COAST OF HONSHU, JAPAN IN THE EXTENDED TAUS. IT
SEEMS THE MAXIMUM ENERGY WITHIN THE POLAR FRONT JET IS SLIDING DOWN
THE EASTERN PERIPHERY OF THE HIGH AMPLITUDE STR AND MAY CAUSE A RE-
GENERATION OF THE MATURE MID-LATITUDE CYCLONE CURRENTLY SOUTH OF
THE KAMCHATKA PENINSULA. HOWEVER, TS 08W IS NOT EXPECTED TO SURVIVE
SUCH A JOURNEY OVER THE TERRAIN OF NORTH KOREA, MAINTAIN IT'S WARM
CORE PROPERTIES IN A CONTINENTAL POLAR AIR MASS, OR MAINTAIN
FORMATION UNDER THE EXPECTED HIGH VWS. THEREFORE, THE HIGH
CONFIDENCE IN THE JTWC FORECAST TRACK REMAINS.//
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