Tropical Storm SAOLA Advisory Sat Oct 21

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (TWENTYSEVEN)
WARNING NR 03//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 27W (TWENTYSEVEN), LOCATED APPROXIMATELY 403 NM EAST-
SOUTHEAST OF SAIPAN, HAS TRACKED NORTHWESTWARD AT 03 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS
AT THE ONSET A WEAK LOW LEVEL CIRCULATION PARTIALLY EXPOSED BEFORE
TUCKING INTO THE OVERCAST CONVECTION. THE INITIAL POSITION IS BASED
ON THE MSI LOOP WITH FAIR CONFIDENCE. THE INITIAL INTENSITY IS HELD
HIGHER THAN DVORAK ESTIMATES OF T2.0 (30 KNOTS) TO REFLECT THE
SUSTAINED CONVECTIVE SIGNATURE. UPPER LEVEL ANALYSIS INDICATES THE
SYSTEM IS IN AN AREA OF LOW (5-10 KNOT) VERTICAL WIND SHEAR (VWS)
WITH A DEVELOPING POLEWARD OUTFLOW CHANNEL INTO A TUTT CELL TO THE
NORTHEAST. SSTS IN THE AREA AT 31 CELSIUS ARE ALSO CONDUCIVE. THE
CYCLONE IS QUASI-STATIONARY BETWEEN COMPETING STEERING INFLUENCES: A
NEAR EQUATORIAL RIDGE TO THE SOUTHWEST AND A SUBTROPICAL RIDGE (STR)
TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THE FORECAST PHILOSOPHY HAS CHANGED TO REFLECT THE VERY SLOW
STORM MOTION, AND CONSEQUENTLY, WEAK INTENSIFICATION.
   B. TS 27W IS FORECAST TO TRACK SLOWLY NORTHWESTWARD AS THE STR
GRADUALLY DOMINATES AND ASSUMES STEERING. DESPITE THE FAVORABLE
ENVIRONMENT, THE LOW LEVEL CIRCULATION IS SLOW TO CONSOLIDATE
RESULTING IN A WEAK/FLARING CONVECTIVE DEVELOPMENT. TS 27W WILL
MAINTAIN A WEAK 35-4O KNOT CENTRAL WIND SPEED UP TO TAU 72.
   C. AFTER TAU 72, TS 27W WILL REMAIN IN A NORTHWESTWARD TRAJECTORY
UNDER THE STEERING INFLUENCE OF THE STR. AS THE SYSTEM SLOWLY GAINS
LATITUDE AND CONSOLIDATES, THE POLEWARD OUTFLOW WILL IMPROVE AND
PROMOTE STEADY INTENSIFICATION, REACHING 45 KNOTS BY TAU 120 AS THE
CYCLONE APPROACHES SAIPAN. THE AVAILABLE NUMERIC GUIDANCE IS WIDELY
SPREAD IN ALL DIRECTIONS, LENDING LOW CONFIDENCE TO THE JTWC TRACK
FORECAST.//
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