Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Storm 12w Warning Nr 06//

From: SIU Weather Processor <[email-masked]>
Date: Wed, 15 Sep 2010 22:13:09 -0500

WDPN31 PGTW 160300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W WARNING NR 06//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 12W (FANAPI), LOCATED APPROXIMATELY 300 NM
SOUTH OF OKINAWA, JAPAN, HAS TRACKED NORTHEASTWARD OVER THE PAST SIX
HOURS AFTER PREVIOUSLY TRACKING SLOWLY WESTWARD. A MID-LATITUDE
SHORT WAVE TROUGH CURRENTLY MOVING OVER KYUSHU HAS WEAKENED THE
SUBTROPICAL RIDGE, CREATING A WEAK STEERING ENVIRONMENT AND ENABLING
TS FANAPI TO TRACK SLOWLY NORTHWARD OVER THE PAST 12 HOURS. THE
SYSTEM IS IN A FAVORABLE ENVIRONMENT FOR DEVELOPMENT WITH AN
ANTICYCLONE OVER THE SYSTEM CENTER, LOW VERTICAL WIND SHEAR, AND
HIGH SEA SURFACE TEMPERATURES. AT THE SAME TIME, ANIMATED
MULTISPECTRAL SATELLITE IMAGERY AND A 152241Z SSMIS MICROWAVE IMAGE
SHOW CONTINUED CONSOLIDATION AS WELL AS VIGOROUS CONVECTION IN THE
EASTERN QUADRANT OF THE CYCLONE. DUE TO STRONG EQUATORWARD OUTFLOW
INTO A TUTT CELL TO THE SOUTHWEST AND THE INTERACTION WITH THE
TROUGH (WHICH IS STARTING TO ENHANCE POLEWARD OUTFLOW), THE SYSTEM
HAS INTENSIFIED BY 15 KNOTS OVER THE PAST 12 HOURS. THE CURRENT
POSITION IS BASED WITH GOOD CONFIDENCE ON VISUAL AND MICROWAVE
IMAGERY. THE CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES FROM
PGTW, KNES, AND PGTW OF 55 KNOTS AS WELL AS FROM DROPSONDES DEPLOYED
BY WC-130 AIRCRAFT CONDUCTING SCIENTIFIC RESEARCH.
3. FORECAST REASONING.
   A. THE TRACK HAS SHIFTED SIGNIFICANTLY TO THE WEST-SOUTHWEST
SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE IN RESPONSE TO
EXPECTED STRENGTHENING OF A SUBTROPICAL RIDGE LOCATED OVER CHINA.
   B. TS 12W IS EXPECTED TO FURTHER INTENSIFY AND REACH TYPHOON
INTENSITY OVER THE NEXT 36 HOURS, WHILE DRIFTING ALONG THE
SOUTHWESTERN PERIPHERY OF THE LOW TO MID-LEVEL STEERING RIDGE, AS IT
CONTINUES TO TAP INTO THE POLEWARD OUTFLOW AHEAD OF THE PASSING
TROUGH. AS THE SYSTEM TURNS WESTWARD, IT WILL START TO LOSE ACCESS
TO THE POLEWARD OUTFLOW THOUGH FANAPI WILL STILL BE IN A FAVORABLE
ENVIRONMENT SUSTAINED BY STRONG EQUATORWARD OUTFLOW. NUMERICAL MODEL
GUIDANCE IS IN INCREASINGLY TIGHTER AGREEMENT WITH THE OVERALL
WESTWARD TRACK. THE JTWC TRACK IS BASED ON CONSENSUS WITH A SLIGHT
INCREASE IN SPEED AFTER TAU 24 AND THE INTENSITY FORECAST IS
SLIGHTLY HIGHER THAN THE NEAR-TERM INTENSITY GUIDANCE.
   C. BEYOND 72 HOURS, TROPICAL STORM 12W IS EXPECTED TO MAKE
LANDFALL AND WEAKEN OVER THE RUGGED TERRAIN OF TAIWAN. BY TAU 96,
INCREASING VERTICAL WIND SHEAR WILL FURTHER WEAKEN THE SYSTEM TO
TROPICAL STROM STRENGTH AS IT MOVES THROUGH THE TAIWAN STRAIT
DISSIPATES OVER CHINA.//

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