Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Storm 16w Warning Nr 13//

From: SIU Weather Processor <[email-masked]>
Date: Sun, 24 Oct 2010 08:35:05 -0500

WDPN32 PGTW 241500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W WARNING NR 13//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 16W (CHABA), LOCATED APPROXIMATELY 690 NM
SOUTH-SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WEST-
NORTHWESTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED WATER
VAPOR SATELLITE IMAGERY SHOWS CONVECTIVE BANDING HAS CONSOLIDATED
AROUND THE LOW LEVEL CIRCULATION CENTER. THE SAME ANIMATION SHOWS
IMPROVED RADIAL OUTFLOW AFTER THE TROPICAL UPPER TROPOSPHERIC TROUGH
TO THE NORTH THAT HAS BEEN RESTRICTING THE POLEWARD CHANNEL MOVED
FURTHER WESTWARD. THE INITIAL POSITION IS BASED ON A 241117 SSMI-S
MICROWAVE IMAGE WITH POOR CONFIDENCE. THE INITIAL INTENSITY IS
AVERAGED BETWEEN PGTW AND RJTD DVORAK ESTIMATES OF 30 AND 42 KNOTS,
RESPECTIVELY. TS 16W IS CURRENTLY TRACKING ALONG THE SOUTHERN
PERIPHERY OF A LOW- TO MID-LEVEL SUBTROPICAL STEERING RIDGE.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE IN FORECAST PHILOSOPHY SINCE
THE PREVIOUS BULLETIN.
   B. AN UPPER LEVEL, MID-LATITUDE TROUGH CURRENTLY TRACKING OVER
CHINA IS EXPECTED TO DIG SOUTHEASTWARD CAUSING THE STEERING RIDGE TO
WEAKEN AND REORIENT. THIS WILL ALLOW TS 16W TO TURN NORTHWARD AROUND
TAU 24. CONSEQUENTLY, THE POLEWARD OUTFLOW IS EXPECTED TO INCREASE
WITH THE SYSTEM'S INITIAL EXPOSURE TO THE UPPER LEVEL WESTERLIES,
FUELING STEADY INTENSIFICATION.
   C. AFTER TAU 72, TS CHABA IS EXPECTED TO VEER SLIGHTLY TO THE
RIGHT AS IT BEGINS EXTRATROPICAL TRANSITION. TOWARDS THE END OF THE
FORECAST PERIOD, THE SYSTEM WILL BEGIN TO WEAKEN AS VERTICAL WIND
SHEAR INCREASES DUE TO STRONG WESTERLIES ASSOCIATED WITH THE
SUBTROPICAL JET STREAM. THE AVAILABLE NUMERIC GUIDANCE IS SPREAD OUT
WITH GFS AND WBAR FAVORING AN EARLIER RECURVATURE. GFDN AND UKMO ARE
INITIALLY IN UNISON WITH THE PACK BEFORE THEY ABRUPTLY TRACK THE
CYCLONE WESTWARD AFTER TAU 36, PRESUMABLY AFTER THE PASSAGE OF THE
UPPER LEVEL TROUGH - AN UNLIKELY SCENARIO AT THIS TIME. THIS TRACK
FORECAST IS IN THE MIDDLE OF THE MODEL ENVELOPE BUT JUST TO THE RIGHT
OF CONSENSUS TO OFFSET THE WESTWARD OUTLIERS.//

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