Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Depression 16w Warning Nr 07//

From: SIU Weather Processor <[email-masked]>
Date: Fri, 22 Oct 2010 21:46:07 -0500

WDPN32 PGTW 230300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL DEPRESSION (TD) 16W, LOCATED APPROXIMATELY 730 NM
SOUTHEAST
OF KADENA, HAS TRACKED WEST-SOUTHWESTWARD AT 09 KNOTS OVER THE PAST
SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND A 222139Z
SSMIS MICROWAVE IMAGE SHOW A BROAD, ILL-DEFINED LOW LEVEL
CIRCULATION CENTER (LLCC). THERE IS LOW CONFIDENCE IN THE INITIAL
POSITION BASED ON THE AFOREMENTIONED SSMIS IMAGE. THE INITIAL
INTENSITY IS BASED ON RJTD AND PGTW DVORAK INTENSITY ESTIMATES OF 25
KNOTS. UPPER LEVEL ANALYSIS INDICATES THE LLCC IS LOCATED IN AN AREA
OF MODERATE VERTICAL WIND SHEAR AND SUBSIDENCE TO THE NORTH INDUCED
BY A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT).
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE IN FORECAST PHILOSOPHY SINCE
THE PREVIOUS BULLETIN. HOWEVER, THERE CONTINUES TO BE A HIGH DEGREE
OF UNCERTAINTY IN THE EXTENDED TRACK AND INTENSITY FORECAST.
   B.  TD 16W IS CURRENTLY TRACKING ALONG THE SOUTHERN PERIPHERY OF
A LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) TO THE NORTH AND IS
EXPECTED TO CONTINUE TRACKING WESTWARD OVER THE NEXT 36 TO 48
HOURS.  AFTER TAU 48, AN UPPER LEVEL MID-LATITUDE TROUGH IS EXPECTED
TO WEAKEN THE STR AND CAUSE TD 16W TO TRACK POLEWARD. AS THE TUTT
CELL CONTINUES TO MOVE WESTWARD AND ALLOWS VERTICAL WIND SHEAR AND
SUBSIDENCE TO CONSEQUENTLY RELAX, THE SYSTEM SHOULD BEGIN TO
STEADILY INTENSIFY.
  C. AS TD 16W INTENSIFIES, IT IS EXPECTED TO TRACK POLEWARD ALONG
THE WESTERN PERIPHERY OF A MID-LEVEL STEERING RIDGE. POLEWARD
OUTFLOW INTO THE UPPER LEVEL TROUGH SHOULD INCREASE BY TAU 72 AND
INCREASE THE INTENSIFICATION RATE. THE MODELS CONTINUE TO SHOW
UNCERTAINTY AS THEY ARE SPREAD IN THE TIMING OF THE POLEWARD TURN.
NOGAPS, GFS, UKMO, AND ECMWF MODELS ARE TRACKING THE SYSTEM
POLEWARD. THE GFDN AND JGSM MODELS ARE OUTLIERS AND ERRONEOUSLY
TRACK TD 16W WESTWARD ALONG A STRONGER STR. THIS FORECAST IS IN
AGREEMENT WITH THE MODELS TRACKING MORE POLEWARD GIVEN THE
EXPECTATION OF A DEEPER MID-LATITUDE TROUGH. ADDITIONALLY, THERE IS
UNCERTAINTY IN THE LATER TAUS OF THE INTENSITY FORECAST. THIS IS DUE
TO AN EXPECTED COLD SURGE ORIGINATING OVER NORTHERN CHINA, WHICH MAY
INCREASE VERTICAL WIND SHEAR IN THE LATER TAUS AND CAUSE THE SYSTEM
TO INTENSITY LESS THAN PREVIOUSLY PREDICTED.//

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