Subject: Pacific-NW: Subj/prognostic Reasoning For Typhoon 16w Warning Nr 21//

From: SIU Weather Processor <[email-masked]>
Date: Tue, 26 Oct 2010 09:40:05 -0500

WDPN32 PGTW 261500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W WARNING NR 21//
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 TRACKED NORTHWESTWARD AT 05 KNOTS DURING
THE PAST SIX HOURS. NEARLY ALL THE DEEP CENTRAL CONVECTION HAD
DISSIPATED AROUND 0600Z, BUT IT HAS SINCE REBUILT OVER THE CENTER. A
STRONG COLD SURGE CONTINUES TO ADVANCE A MODIFIED POLEWARD AIRMASS
EQUATORWARD. THIS SURGE APPEARS TO HAVE HAD LITTLE IMPACT ON THE TY
THUS FAR, DESPITE NORTHEASTERLIES BEGINNING TO WEAKLY FILTER IN
BENEATH THE CENTRAL CONVECTION. DUAL EXHAUST MECHANISMS PERSIST AND
ARE POSITIONED TO AID INTENSIFICATION. VERTICAL WIND SHEAR
FLUCTUATES BETWEEN LOW AND MODERATE, WITH THE LOW LEVEL FLOW BEING
NEARLY 180 DEGREES OUT OF PHASE WITH THE UPPER LEVEL SOUTH-
WESTERLIES. A NARROW EXTENSION OF A DEEP LAYER STEERING RIDGE TO THE
EAST HAS CONTINUED TO ADVANCE THE TY NORTHWEST.
3. FORECAST REASONING.
   A. THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST PHILOSOPHY.
HOWEVER, TRACK SPEEDS HAVE BEEN ALTERED, ESPECIALLY IN THE LATER
TAUS, TO ACCOUNT FOR A SLOWER CONSENSUS AND A DELAYED TURN TO THE
NORTH.
   B. THE RIDGE EXTENSION WILL BEGIN TO ERODE OVER THE NEXT 06 TO 12
HOURS AND WILL ALLOW THE TY TO TRACK MORE TOWARDS THE NORTH. 500 MB
HEIGHT ANALYSIS INDICATES THAT THE RIDGE HAS ALREADY BEGUN TO
RETREAT TO THE EAST. AS CHABA TRACKS POLEWARD ALONG THE FLATTENED
WESTERN EXTENSION OF THE DEEP LAYER RIDGE, IT WILL CONTINUE TO
INTENSIFY, BUT AT A SLOWER RATE. POLEWARD OUTFLOW WILL WEAKEN AS AN
UPPER LEVEL TROUGH PULLS TO THE NORTHEAST INTO THE DEEP MID-
LATITUDES. IT REMAINS UNCERTAIN WHAT IMPACT THE COLD SURGE WILL HAVE
ON THE INTENSITY FORECAST, BUT CURRENTLY THE SYSTEM REMAINS
UNSCATHED. TOTAL PRECIPITABLE WATER PRODUCTS SHOW A WELL-ISOLATED
SYSTEM THAT CONTINUES TO PULL IN AIR FROM THE DEEP TROPICS. AROUND
TAU 48 THE TY WILL SIT JUST SOUTH OF OKINAWA NEAR 90 KNOTS. MODEL
GUIDANCE THROUGH THE FIRST 2 DAYS SHOWS A GENERAL SLOW POLEWARD
TREND. BECAUSE THE SYSTEM HAS YET TO TURN NORTH-NOTHWEST FROM
NORTHWEST THE ENTIRE FORECAST TRACK HAS BEEN SHIFTED SLIGHTLY WEST
OF THE PREVIOUS FORECAST. IN ADDITION, THE MODEL CONSENSUS HAS ALSO
SHIFTED WEST.
   C. THE CYCLONE WILL BEGIN TO ACCELERATE AROUND TAU 72 AS IT
ROUNDS THE RIDGE AXIS INTO THE MID-LATITUDES, AND WILL ALSO BEGIN TO
WEAKEN UNDER INCREASED VERTICAL WIND SHEAR. EXTRATROPICAL TRANSITION
WILL ALSO BEGIN SHORTLY THEREAFTER AS THE SYSTEM INTERACTS WITH A
BAROCLINIC BOUNDARY RUNNING SOUTH OF JAPAN. THE CYCLONE WILL QUICKLY
TRANSITION FROM TROPICAL TO EXTRATROPICAL BY TAU 120, JUST NORTH OF
TOKYO. THE FORECAST HAS BEEN SHIFTED FURTHER INLAND OVER HONSHU TO
ACCOUNT FOR A CONSENSUS THAT HAS WALKED WEST. GIVEN THE WESTERLIES
ALOFT IT IS UNLIKELY THAT THE SYSTEM WILL ADVANCE ANY FARTHER WEST
OVER JAPAN THAN ALREADY FORECAST, DESPITE THE GFDN SOLUTION THAT
WANTS TO PULL THE SYSTEM INTO THE SEA OF JAPAN. GFS AND ECMWF,
THOUGH SOMEWHAT FASTER THAN THE OFFICIAL FORECAST, RESOLVE FORECAST
TRACKS THAT ARE CONSISTENT WITH A SYSTEM ENTERING THE MID-LATITUDES,
AND HAVE THE CYCLONE ACCELERATING TO THE NORTHEAST AFTER SKIRTING
HONSHU.//

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