MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (TEMBIN) WARNING NR
40//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 15W (TEMBIN), LOCATED APPROXIMATELY 155 NM
NORTHEAST OF TAIPEI, TAIWAN, HAS TRACKED NORTH-NORTHEASTWARD AT 11
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY, IN ADDITION TO RADAR IMAGERY FROM ISHIGAKIJIMA, JAPAN,
SHOWS THE LOW LEVEL CIRCULATION CENTER (LLCC) REMAINS ON THE
NORTHEASTERN QUADRANT OF A LARGE, BROAD REGION OF DEEP CONVECTION.
BASED ON A 281328Z ASCAT PASS, THE WINDS NEAR THE CENTER ARE
STRONGEST WITHIN THE SOUTHEASTERN QUADRANT OF THE LLCC, AND INDICATE
SPEEDS AROUND 50 KNOTS. THIS CURRENT INTENSITY OF 50 KNOTS IS BASED
ON THE ASCAT PASS, AND IS SLIGHTLY HIGHER THAN DVORAK ESTIMATES FROM
PGTW BUT IS IN GOOD AGREEMENT WITH THE 3.0/3.5 DVORAK FROM RJTD.
UPPER LEVEL ANALYSIS INDICATES TS 15W IS SLIGHTLY POLEWARD OF A
SUBTROPICAL RIDGE (STR) AXIS THAT EXTENDS FROM CENTRAL JAPAN TO
DIRECTLY OVER TAIWAN. THE UPPER LEVEL REFLECTION OF THE DEEP STR
INDICATES WINDS FROM THE EAST ARE PRODUCING LOW TO MODERATE LEVELS
OF VERTICAL WIND SHEAR (VWS) ALONG THE EASTERN AND NORTHEASTERN
PORTIONS OF THE LLCC. TS 15W IS CURRENTLY TRACKING AROUND THE MID-
LEVEL REFLECTION OF THE STR WHICH HAS BECOME THE DOMINANT STEERING
MECHANISM.
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
B. TS 15W IS FORECAST TO TRACK NORTH-NORTHEASTWARD THROUGH TAU 36
UNDER THE INFLUENCE OF THE STR. THIS IS NOT EXPECTED TO SHIFT UNTIL
THE SYSTEM MAKES LANDFALL AROUND TAU 36 AND SHIFTS MORE EASTWARND AS
THE STR SHIFTS IN RESPONSE TO THE REMNANTS OF EXTRATROPICAL STORM
16W (BOLAVEN) TRACKING TO THE NORTH OF THE STR. TS 15W WILL STRUGGLE
TO MAINTAIN INTENSITY OVER THE NEXT 12 HOURS IN AN INCREASINGLY
HARSH UPPER LEVEL ENVIRONMENT AS VWS INCREASES AS TS 15W MOVES
FURTHER POLEWARD OF THE UPPER LEVEL STR AXIS. SEA SURFACE
TEMPERATURES (SSTS) REMAIN FAVORABLE AT 26 TO 28 CELSIUS AND WILL BE
THE PRIMARY FACTOR ALLOWING TS 15W TO MAINTAIN INTENSITY FOR THE
NEXT 12 HOURS. THE STEADY INCREASE IN VWS WILL BEGIN TO WEAKEN THE
SYSTEM BEYOND TAU 12. SSTS ARE EXPECTED TO SLOWLY DECREASE THROUGH
LANDFALL, APPROXIMATELY TAU 36, WHICH WILL ALSO FURTHER WEAKEN TS
15W. BY TAU 36 INCREASING INTERACTION WITH AN APPROACHING MID-
LATITUDE TROUGH WILL BEGIN THE EXTRATROPICAL TRANSITION PROCESS.
FRICTIONAL EFFECTS AND CONTINUED INTERACTION WITH THE TROUGH WILL
LEAD TO COMPLETE EXTRATROPICAL SYSTEM BY TAU 48. MODEL GUIDANCE IS
IN GOOD AGREEMENT WITH THE TRACK, BUT APPEARS TO SLOW THE SYSTEM AS
IT APPOACHES THE KOREAN PENINSULA. MODEL FIELDS APPEAR TO INDICATE
THE LLCC IS LOST WITHIN THE APPROACHING TROUGH, THUS LOSE THE
ABILITY TO TRACK THE REMNANTS OF THE LLCC. BASED ON THIS ASSESSMENT,
THE CURRENT FORECAST KEEPS THE TRACK FASTER THAN THE CONSENSUS OF
MODEL GUIDANCE, BUT STILL HAS HIGH CONFIDENCE.//
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