Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Depression 14w Warning Nr 05//

From: SIU Weather Processor <[email-masked]>
Date: Tue, 5 Oct 2010 21:04:14 -0500

WDPN31 PGTW 060300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 14W WARNING NR 05//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL DEPRESSION (TD) 14W, LOCATED APPROXIMATELY 260 NM
WEST-SOUTHWEST OF HONG KONG, CHINA, HAS TRACKED EASTWARD AT 02 KNOTS
OVER THE PAST SIX HOURS. ANIMATED WATER VAPOR IMAGERY INDICATES
SIGNIFICANT SHEARING OF THE SYSTEM IN THE UPPER LEVELS AND MULTI-
SPECTRAL ANIMATION SHOWS A SIGNIFICANT DECREASE IN CONVECTION.
CORE CONVECTION IN THE SYSTEM HAS NEARLY COMPLETELY ENDED DURING
THE PAST SIX HOURS. THE LOW-LEVEL CIRCULATION (LLCC) IS POORLY-
DEFINED AND POSTION CONFIDENCE IS LOW. SYNOPTIC OBSERVATIONS FROM
HAINAN ISLAND, LEIZHOU PENINSULA, AND COASTAL CHINA CONFIRM THAT THE
LOWEST SURFACE PRESSURES ARE IN THE QIONGSHOU STRAIT. A 052220Z
MICROWAVE IMAGE INDICATES THAT WHAT CONVECTION REMAINS HAS SHEARED
FROM THE LLCC DURING THE PAST THREE HOURS. THE CURRENT INTENSITY IS
BASED ON SURFACE OBSERVATIONS WITHIN THE REGION. DUE TO THE RAPIDLY
DECAYING DEEP CONVECTION, DVORAK ESTIMATES ARE UNCLASSIFIABLE.
3. FORECAST REASONING.
   A. THE FORECAST PHILOSOPHY HAS NOT CHANGED SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. TD 14W IS IN A WEAK STEERING ENVIRONMENT AND DRIFTING INTO AN
INCREASINGLY UNFAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE TO
STRONG VERTICAL WIND SHEAR (VWS) AND DECREASING OCEAN HEAT CONTENT.
A 05/12Z UPPER AIR SOUNDING FROM HONG KONG SHOWS A LAYER OF DRY
EASTERLIES BETWEEN 925 MB AND 700 MB THAT PORTENDS TO SOME
DRIER AIR BECOMING DRAWN INTO THE SYSTEM AT THE BOUNDARY LEVEL.
DURING THE PAST 12 HOURS A WEAK SHORT WAVE TROUGH TRACKING OVER
SOUTHERN CHINA MOVED EASTWARD AND WAS FOLLOWED BY A DEVELOPING
RIDGE. THE ASSOCIATED HEIGHT RISES AND ANTICYCLONIC TURNING ARE
ACTING TO SUPPRESS THE POLEWARD OUTFLOW THAT HAS BEEN A KEY IN
SUSTAINING THE SYSTEM AS IT TRACKED OVER HAINAN ISLAND. STRONG UPPER-
LEVEL WESTERLIES NORTH OF 20N WILL COMBINE WITH GRADIENT LEVEL
NORTHEASTERLY FLOW FLOWING OUT OF A 1020 MB HIGH SETTLING OVER
SHANGHAI TO PRODUCE VWS VALUES IN EXCESS OF 30 KNOTS. TD 14W IS
BOXED IN AN UNFAVORABLE ENVIRONMENT AND ANY EASTWARD MOTION WILL
RESULT IN MORE VWS AND FURTHER WEAKENING. THE COMBINATION OF SHEAR
ALOFT AND DRYING AT THE BOUNDARY LEVELS WILL WEAKEN AND DE-COUPLE
THE STORM BETWEEN TAU 00 AND TAU 12, AND THE SYTEM WILL DISSIPATE
OVER WATER BY TAU 12. AVAILABLE DYNAMIC AIDS ARE IN POOR AGREEMENT
AS TO TRACK DUE TO LACK OF STEERING FLOW AND WEAK INTENSITY OF THE
SYSTEM. THEREFORE THE TRACK FORECAST IS BASED ON A CONSTANT RATE OF
MOVEMENT THROUGH TAU 24.//

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