Tropical Storm TEMBIN Advisory gio, 23.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (TEMBIN) WARNING NR 17//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 15W (TEMBIN), LOCATED APPROXIMATELY 185 NM SOUTHEAST
OF TAIPEI, TAIWAN, HAS TRACKED WESTWARD AT 02 KNOTS OVER THE PAST
SIX HOURS. ANIMATED MULTISPECTRAL AND ENHANCED INFRARED SATELLITE
IMAGERY SHOWED A BRIEF PERIOD WHEN THE EYE WAS CLEARED BUT SINCE
THEN HAS BECOME MORE CLOUD OBSCURED. A 230006Z SSMIS 91 GHZ
MICROWAVE IMAGE REVEALS A NEARLY UNIFORM CONCENTRIC DEEP EYEWALL
STRUCTURE THAT IS SLIGHTLY FRAGMENTED OVER THE SOUTHWESTERN
QUADRANT. THE CURRENT POSITION IS BASED ON RADAR FIXES FROM JAPAN
AND TAIWAN, ALONG WITH THE SSMIS IMAGE, WITH HIGH CONFIDENCE. THE
CURRENT INTENSITY IS BASED ON THE HIGHER SIDE OF DVORAK INTENSITY
ESTIMATES, RANGING FROM 77 TO 102 KNOTS FROM RJTD AND PGTW/KNES
RESPECTIVELY, DUE TO THE VIGOROUS EYEWALL STRUCTURE. TRACK SPEEDS
CONTINUE TO BE SLOW AS THE PRIMARY STEERING INFLUENCE, A DEEP
LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH, HAS BEEN WEAKENED BY A
TRANSITING MID-LATITUDE TROUGH EXITING THE KOREAN PENINSULA. UPPER-
LEVEL ANALYSIS INDICATES THE POLEWARD OUTFLOW TOWARDS THE TROPICAL
UPPER-TROPOSPHERIC TROUGH CELL THAT WAS LOCATED OVER SOUTHERN HONSHU
HAS BEEN SHUT DOWN AS THE CELL FILLED INTO TROUGHING. CURRENTLY
THERE IS VERY WEAK POLEWARD OUTFLOW INTO THE UPPER-LEVEL TROUGHING
BUT EQUATORWARD OUTFLOW REMAINS ROBUST. THE SELF-INDUCED MESO-
ANTICYCLONE IS STILL IN PLACE OVER THE LLCC PROVIDING FOR MODERATE
DIVERGENCE ALOFT AND WEAK (05-10 KNOTS) VERTICAL WIND SHEAR (VWS).
SEA SURFACE TEMPERATURES WITHIN THE REGION REMAIN FAVORABLE (28 TO
30 CELSIUS) ALONG THE FORECAST TRACK. TY 15W IS CURRENTLY BEING
STEERED WESTWARD BY A WEAK EXTENSION OF THE STR, AS INDICATED BY THE
35 KNOT 500 MB EASTERLIES IN THE 230000Z RADIOSONDE FROM ISHIGAKI-
JIMA (24.33N 124.16E).
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 15W WILL CONTINUE TO STEER WESTWARD INTO TAIWAN VIA THE
WEAK EXTENSION OF THE STR. FURTHER INTENSIFICATION IS EXPECTED DUE
TO CONTINUED FAVORABLE ENVIRONMENTALS MENTIONED EARLIER. BY TAU 24
TY 15W SHOULD MAKE LANDFALL WHERE THE LLCC WILL BEGIN TO SLIGHTLY
WEAKEN DUE TO LAND INTERACTION AND LACK OF OCEAN HEAT. HOWEVER, TY
15W IS EXPECTED TO EMERGE OFF THE WESTERN COAST OF TAIWAN AFTER ONLY
BEING OVERLAND FOR APPROXIMATELY 12 HOURS. THE SYSTEM WILL THEN
SLOWLY DRIFT WEST-SOUTHWESTWARD IN A WEAK STEERING ENVIRONMENT WITH
A BUILDING NEAR EQUATORIAL RIDGE TO THE SOUTHEAST AND A DEEPLY
DIGGING TROUGH OVER EASTERN CHINA. SLOW INTENSIFICATION IS EXPECTED
DURING THIS TIME DUE TO A POCKET OF WARM OCEAN HEAT CONTENT, WARM
SEA SURFACE TEMPERATURES, AND INCREASING POLEWARD OUTFLOW OUT AHEAD
OF ANOTHER DIGGING TROUGH. THERE IS HIGH CONFIDENCE IN THE TRACK
FORECAST UP TO THE LANDFALL POSITION AND INTO THE TAIWAN STRAIT, BUT
BY TAU 48 FORECAST CONFIDENCE DEGRADES DUE TO THE COMPLEX TIMING OF
THE SYNOPTIC FEATURES.
   C. IN THE EXTENDED FORECAST TY 15W IS EXPECTED TO CONTINUE A SLOW
DRIFT SOUTH AND THEN EVENTUALLY BACK EAST IN A COUNTERCLOCKWISE LOOP
AS THE STEERING ENVIRONMENT REMAINS WEAK. THE SYSTEM SHOULD BEGIN TO
WEAKEN UNDER INCREASINGLY UNFAVORABLE CONDITIONS DUE TO STRONGER VWS
FROM TY 16W'S OUTFLOW. ADDITIONALLY, SOME BINARY INTERACTION WITH
THE MUCH LARGER TY 16W IS EXPECTED WHICH SHOULD FURTHER ATTRACT THE
LLCC BACK EASTWARD ALONG WITH UPPER-LEVEL WEST-SOUTHWEST FLOW AT THE
TIME. OBJECTIVE AID GUIDANCE CONTINUES TO COME INTO BETTER AGREEMENT
TOWARDS THE LOOPING MOTION WITH THE EXCEPTION OF THE WBAR, EGRR, AND
GFDN. THESE THREE TRACKERS WERE DISCOUNTED DUE TO UNREALISTIC MOTION
INTO, AND BEYOND, THE TROUGHING THAT WILL DEVELOP AT THIS TIME.
THERE IS LOW CONFIDENCE IN THIS PORTION OF THE TRACK FORECAST DUE TO
UNCERTAINTIES IN THE TIMING OF SYNOPTIC FEATURES AND COMPLEX LOOPING
MOTION.//
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