Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 16w Warning Nr 23//

From: SIU Weather Processor <[email-masked]>
Date: Tue, 26 Oct 2010 22:41:05 -0500

WDPN32 PGTW 270300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W WARNING NR 23//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 16W (CHABA), CURRENTLY LOCATED 375 NM SOUTH OF
KADENA AB, OKINAWA, HAS SHOWN ERRATIC (NEARLY QUASI-STATIONARY)
MOVEMENT DURING THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY INDICATES CONVECTION HAS DEEPENED AND CONSOLIDATED OVER THE
SYSTEM DURING THE PAST SIX HOURS IN RESPONSE TO AN ENHANCED POLEWARD
OUTFLOW CHANNEL. RECENT VISUAL SATELLITE IMAGERY SHOWS OVERSHOOTING
CLOUD TOPS NEAR THE TY CORE AND THE BEGINNINGS OF AN EYE. THERE IS
HIGH CONFIDENCE IN THE CURRENT POSITION BASED ON A 26/2228Z SSMIS
91H MICROWAVE IMAGE INDICATING A DEFINITIVE MICROWAVE EYE. THE
CURRENT INTENSITY ANALYSIS IS BASED ON DVORAK CURRENT INTENSITY (CI)
ESTIMATES OF 102 KNOTS FROM PGTW AND 90 KNOTS FROM RJTD. ANIMATED
WATER VAPOR IMAGERY INDICATES WELL-DEVELOPED OUTFLOW CHANNELS EXIST
ON ALL QUADRANTS OF THE STORM. CONTINENTAL POLAR (CP) AIR
ENTRAINMENT FROM A RECENT COLD SURGE APPEARS TO BE MINIMAL THUS FAR,
PRODUCING LITTLE IMPEDIMENT ON STORM DEVELOPMENT. THIS IS LIKELY AN
EFFECT OF PARALLEL NORTHEASTERLY FLOW ALONG THE RYUKUS RATHER THAN
PERPENDICULAR NORTHWESTERLIES. A TOTAL PRECIPITABLE WATER LOOP DOES
SHOW ONE PULSE OF DRIER AIR MADE IT INTO THE SYSTEM CORE BUT WAS
QUICKLY ABSORBED. RECENT SURFACE ANALYSIS SHOWS WINDS ARE BACKING
AND INCREASING OVER THE RYUKUS INDICATING BOUNDARY LEVEL FLOW OF CP
AIR INTO THE STORM WILL SOON INCREASE. VERTICAL WIND SHEAR IS
MINIMAL SOUTH OF 28N, WHERE IT INCREASES RAPIDLY. A WESTERN
EXTENSION OF THE SUB-TROPICAL RIDGE ACTED TO DRIVE THE STORM
WESTWARD BETWEEN 26/06Z AND 26/18Z BUT HAS WEAKENED SIGNIFICANTLY,
CREATING A ALLEY FOR THE STORM TO TURN POLEWARD. 3. FORECAST
REASONING.
   A. THE TRACK FORECAST THROUGH TAU 36 HAS BEEN ACCELERATED
SLIGHTLY FROM THE PREVIOUS FORECAST BASED ON INDICATIONS THE STORM
WILL ACCELERATE AS IT UNDERGOES EXTRA-TROPICAL TRANSITION SOONER.
B. AS TYPHOON 16W TURNS POLEWARD TOWARD A WEAKNESS IN THE
RIDGE, IT WILL REMAIN EAST OF THE RYUKUS. NUMERICAL MODEL GUIDANCE
HAS COME INTO BETTER AGREEMENT WITH THIS SCENARIO. LACK OF COUPLING
WITH THE MID-LATITUDE WESTERLIES WILL RESULT IN A SLOW AND GRADUAL
TURN TO THE NORTH. INTERACTION WITH THE BAROCLINIC ZONE WILL
COMMENCE AS THE STORM APPROACHES 28N. IN THE SAME REGION, THERE WILL
BE A SHARP INCREASE IN VERTICAL WIND SHEAR, AS THE UPPER
TROPOSPHERIC WESTERLIES INCREASE TO OVER 75 KNOTS NORTH OF 29N. THE
COMBINATION OF INCREASING VERTICAL WIND SHEAR AND ENTRAINMENT OF
MODIFIED CONTINENTAL POLAR AIR INTO THE BOUNDARY LEVEL WILL AFFECT A
SHARP EXTRA-TROPICAL TRANSITION AND PRONOUNCED DECAY OF THE SYSTEM
BETWEEN TAU 48 AND 72. TY 16W WILL COMPLETE EXTRA-TRANSITION AND
BECOME A VIGOROUS BAROCLINIC LOW. NUMERICAL MODEL GUIDANCE HAS COME
INTO BETTER AGREEMENT IN THE EARLY TAUS. THE TRACK FORECAST THROUGH
TAU 72 STAYS JUST WEST AND JUST FASTER THAN CONSENSUS THROUGH TAU 72.
   C. AFTER TAU 72, TY 16W IS EXPECTED TO TRACK BETWEEN THE JAPANESE
ALPS AND THE KANTO PLAIN AS A SEVERE GALE TO STORM FORCE LOW BEFORE
RETURNING TO THE WESTERN PACIFIC WELL SOUTH OF MISAWA, JAPAN.
NUMERICAL MODEL GUIDANCE HAS COME INTO TIGHTER AGREEMENT IN THE
LATER TAUS AND THE JTWC FORECAST TRACK HAS REMAINED PERSISTENT. THE
FORECASTED SPEED IS FASTER THAN MODEL CONSENSUS AT TAU 96 AND 120 IN
ANTICIPATION OF STEERING BY THE POLAR FRONT JET.//

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