WDPN32 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (SEVEN) WARNING NR 
12//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 07W (SEVEN), LOCATED APPROXIMATELY 263 NM 
EAST-SOUTHEAST OF POHNPEI, HAS TRACKED NORTHWESTWARD AT 05 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE 
IMAGERY DEPICTS A DEEPENING CENTRAL DENSE OVERCAST FEATURE OBSCURING 
THE LOW LEVEL CIRCULATION CENTER (LLCC). A 091051Z GMI 89GHZ 
MICROWAVE IMAGE DEPICTS BROKEN CONVECTIVE BANDING WRAPPING INTO THE 
PARTIALLY EXPOSED LLCC JUST NORTHEAST OF THE BULK OF CONVECTION. THE 
INITIAL POSITION IS BASED ON THE AFOREMENTIONED MICROWAVE IMAGE WITH 
FAIR CONFIDENCE. THE INITIAL INTENSITY OF 40 KNOTS IS BASED ON AN 
AVERAGE OF DVORAK INTENSITY ESTIMATES FROM PGTW, KNES, AND RJTD. 
UPPER LEVEL ANALYSIS INDICATES A MARGINAL ENVIRONMENT UNDER EASTERLY 
DIFFLUENT FLOW WITH MODERATE (20-25 KNOTS) VERTICAL WIND SHEAR 
(VWS); HOWEVER, SEA SURFACE TEMPERATURES ABOVE 29 CELSIUS ARE VERY 
FAVORABLE. TS 07W CONTINUES TO TRACK SLOWLY NORTHWESTWARD AS THE SUB-
TROPICAL RIDGE (STR) TO THE NORTH BUILDS IN TO ASSUME STEERING.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM 
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 07W WILL CONTINUE TO SLOWLY TURN WEST-NORTHWESTWARD AS THE 
BUILDING STR ASSUMES STEERING. UPPER LEVEL ENVIRONMENTAL CONDITIONS 
WILL REMAIN MARGINAL OVER THE NEXT 48 HOURS CAUSING GRADUAL 
INTENSIFICATION. BEYOND TAU 48, AN IMPROVING ENVIRONMENT WITH 
DECREASING VWS (10-15 KNOTS) AND AN INCREASING POLEWARD OUTFLOW 
CHANNEL WILL LEAD TO FURTHER INTENSIFICATION.
   C. IN THE EXTENDED TAUS, TS 07W WILL REMAIN ON A WEST-
NORTHWESTWARD TRAJECTORY UNDER THE STEERING INFLUENCE OF THE STR. 
CONTINUED FAVORABLE ENVIRONMENTAL CONDITIONS WILL SUPPORT 
INTENSIFICATION, REACHING A PEAK INTENSITY OF 95 KNOTS AT TAU 120. 
BY THE END OF THE FORECAST PERIOD AN APPROACHING MID-LATITUDE TROUGH 
WILL CAUSE THE STEERING STR TO WEAKEN, ALLOWING TS 07W TO TURN 
SLIGHTLY POLEWARD TOWARDS A BREAK IN THE RIDGE. DYNAMIC MODEL 
GUIDANCE IS IN BETTER AGREEMENT REGARDING THE TRACK AND THE TIMING 
OF THE NORTHWESTWARD ACCELERATION; HOWEVER, SLIGHT MODEL DIVERGENCE 
AT TAU 24 RESULTS IN A 200-NM SPREAD BY TAU 120 LEADING TO LOW 
CONFIDENCE IN THE OVERALL JTWC TRACK FORECAST.//
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