Tropical Storm TEMBIN Advisory Mon Aug 20

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (TEMBIN) WARNING NR 07//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 15W (TEMBIN), LOCATED APPROXIMATELY 420 NM SOUTH-
SOUTHEAST OF TAIPEI, TAIWAN, HAS TRACKED NORTH-NORTHEASTWARD AT 05
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED IMAGERY
AND A 201157Z SSMIS IMAGE INDICATE IMPROVED EYEWALL CONSOLIDATION
OVER THE PAST SIX HOURS WITH A 25 NM ROUND EYE EVIDENT SURROUNDED BY
A MORE SYMMETRIC EYEWALL WITH COLDER CLOUD TOP TEMPERATURES. THERE
IS GOOD CONFIDENCE IN THE INITIAL POSITION BASED ON THE ROUND EYE
STRUCTURE IN SATELLITE IMAGERY. UPPER-LEVEL ANALYSIS INDICATES NEAR-
RADIAL OUTFLOW WITH POLEWARD OUTFLOW ENHANCED BY A STRONG TUTT CELL
NEAR 27N 135E. THE ONLY LIMITING FACTOR EVIDENT IN ANIMATED WATER
VAPOR IMAGERY IS CONVERGENT FLOW OVER THE NORTHWEST PERIPHERY OF THE
SYSTEM. AS A RESULT OF THE VERY FAVORABLE ENVIRONMENTAL CONDITIONS,
TY 15W HAS RAPIDLY INTENSIFIED OVER THE PAST 24 HOURS GOING FROM A
45-KNOT INTENSITY AT 19/12Z TO THE 20/12Z INITIAL INTENSITY OF 110
KNOTS, WHICH IS BASED ON AN AVERAGE OF THE LATEST DVORAK ESTIMATES
RANGING FROM 102 KNOTS (RJTD, KNES) TO 115 KNOTS (PGTW). TY 15W IS
EMBEDDED WITHIN A WEAK STEERING ENVIRONMENT AND HAS TRACKED SLOWLY
AND ERRATICALLY NORTHWARD ALONG THE NORTHWEST PERIPHERY OF THE LOW-
TO MID-LEVEL NEAR-EQUATORIAL RIDGE (NER).
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 15W IS FORECAST TO TRACK SLOWLY NORTHWARD TO NORTH-
NORTHWESTWARD WITHIN A WEAK STEERING ENVIRONMENT THROUGH TAU 36.
NEAR TAU 36, A DEEP MIDLATITUDE TROUGH WILL TRACK ACROSS THE KOREAN
REGION RESULTING IN A TEMPORARY SLOW-DOWN OR PERHAPS QUASI-
STATIONARY MOTION EAST OF TAIWAN; HOWEVER, THIS IS EXPECTED TO BE
SHORT-LIVED AS THE TROUGH IS EXPECTED TO RAPIDLY TRANSIT EASTWARD.
AFTER TAU 48, THE SUBTROPICAL RIDGE IS FORECAST TO RE-BUILD OVER
EASTERN CHINA AND THE EAST CHINA SEA PROVIDING A WESTWARD STEERING
INFLUENCE. TY 15W IS FORECAST TO CONTINUE INTENSIFYING THROUGH TAU
72 UNDER FAVORABLE CONDITIONS AND SHOULD REACH A PEAK INTENSITY OF
125 KNOTS PRIOR TO MAKING LANDFALL OVER TAIWAN.
   C. IN THE EXTENDED TAUS, TY 15W SHOULD ACCELERATE AND TRACK
WESTWARD INTO THE TAIWAN STRAIT AND WILL MAKE ITS SECOND LANDFALL
NORTHEAST OF HONG KONG NEAR TAU 96. THE SYSTEM IS EXPECTED TO
MAINTAIN MINIMAL TYPHOON STRENGTH AS IT EMERGES OVER THE TAIWAN
STRAIT BUT SHOULD WEAKEN SIGNIFICANTLY AFTER SECOND LANDFALL DUE TO
FRICTIONAL EFFECTS. THE BULK OF THE DYNAMIC MODEL GUIDANCE IS IN
GOOD AGREEMENT WITH A 170 NM SPREAD AT TAU 120; HOWEVER, THE UKMO
MODEL ERRONEOUSLY DRIVES THE SYSTEM NORTHWARD INTO THE STR AND IS
DISCOUNTED. ADDITIONALLY, THE GFS MODEL IS NOW INDICATING STRONG
BINARY INTERACTION WITH TS 16W AFTER TAU 72, WHICH IS DEEMED
UNLIKELY AT THIS POINT. THE TWO SYSTEM CENTERS ARE CURRENTLY
SEPARATED BY 930 NM AND, BASED ON THE 20/12Z FORECASTS, WILL
APPROACH TO ABOUT 680 NM BY TAU 72. UNLESS THERE IS A SIGNIFICANT
TRACK CHANGE I.E., A LONGER QUASI-STATIONARY PERIOD EAST OF TAIWAN,
BINARY INTERACTION IS UNLIKELY. OVERALL, THERE IS HIGH CONFIDENCE IN
THE FORECAST TRACK.//
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