Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Storm 10w Warning Nr 12//

From: SIU Weather Processor <[email-masked]>
Date: Sat, 4 Sep 2010 10:09:04 -0500

WDPN33 PGTW 041500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 10W WARNING NR 12//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 10W (MALOU), LOCATED APPROXIMATELY 35 NM
NORTH-NORTHWEST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWARD
AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE
IMAGERY SHOWS DEVELOPING CENTRAL CONVECTION OVER A BROAD AREA OF
CIRCULATION. THE MAJORITY OF THE DEEP CONVECTION IS ON THE EASTERN
TO SOUTHEASTERN PERIPHERY OF THE LOW LEVEL CIRCULATION CENTER
EMBEDDED WITHIN A MONSOON GYRE-LIKE PATTERN. TS 10W APPEARS TO HAVE
MERGED WITH THE TROPICAL DISTURBANCE PREVIOUSLY LOCATED TO THE EAST.
THE INITIAL POSITION IS BASED ON THE PGTW AND RJTD SATELLITE FIX
ALONG WITH RADAR FROM JAPAN. THE INITIAL INTENSITY IS BASED ON THE
PGTW, RJTD, AND KNES DVORAK ESTIMATES RANGING FROM 30 TO 35 KNOTS.
TS 10W IS LOCATED IN AN AREA OF DIVERGENCE ALOFT, ALTHOUGH AN UPPER
LEVEL MID-LATITUDE TROUGH APPEARS TO BE CAUSING SUBSIDENCE ALONG THE
NORTHERN PERIPHERY OF THE SYSTEM, LIMITING POLEWARD OUTFLOW.
HOWEVER, EQUATORWARD OUTFLOW REMAINS GOOD.
3. FORECAST REASONING.
   A. THE FORECAST HAS TRENDED EASTWARD BECAUSE TS 10W HAS TRACKED
NORTHWARD WITH THE SUBTROPICAL STEERING RIDGE WEAKENING SOONER THAN
EXPECTED. HOWEVER, THE FUNDAMENTAL PHILOSOPHY OF THE TRACK AND
INTENSITY FORECASTS REMAINS THE SAME.
   B. TS 10W IS CURRENTLY TRACKING NORTHWARD ALONG THE WESTERN
PERIPHERY OF A SUBTROPICAL STEERING RIDGE. AN UPPER AIR OBSERVATION
FROM NAZE INDICATES MID-LEVEL SOUTHEASTERLY FLOW ALSO SHOWING THE
STEERING RIDGE HAS WEAKENED. TS MALOU IS EXPECTED TO CONTINUE
TRACKING NORTHEASTWARD. AROUND TAU 48, TS 10W WILL WEAKEN AS IT
INTERACTS WITH THE MID-LATITUDE WESTERLIES AND TRACKS OVER COOLER
SEA SURFACE TEMPERATURES IN THE YELLOW SEA. THE SYSTEM SHOULD REACH
SOUTH KOREA AFTER TAU 72.
   C. AFTER TAU 72, TS MALOU IS EXPECTED TO CONTINUE WEAKENING AS IT
TRACKS OVER LAND AND AS IT FURTHER INTERACTS WITH THE MID-LATITUDE
WESTERLIES. THE NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT, BUT
DEPICT VARYING RECURVATURE TIMING IN RESPONSE TO THE WEAKENING
STEERING RIDGE. THIS FORECAST IS IN AGREEMENT WITH THE EGRR AND
ECMWF MODELS, WHICH CURVE THE SYSTEM INTO THE WESTERLIES LATER THAN
THE OTHER MODELS.//

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