Subject: Pacific-NW: Subj/prognostic Reasoning For Tropical Depression 10w Warning Nr 01//

From: SIU Weather Processor <[email-masked]>
Date: Sun, 03 Aug 2008 21:14:09 -0500

WDPN31 PGTW 040300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 10W WARNING NR 01//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
A. TROPICAL DEPRESSION (TD) 10W HAS CONSOLIDATED QUICKLY OVER THE PAST
12 HOURS AS IT HAS TRACKED AWAY FROM NORTHERN LUZON. ANIMATED MULTI-
SPECTRAL SATELLITE IMAGERY INDICATES DEEP CONVECTIVE BANDING FORMING
OVER THE SOUTHERN SEMI-CIRCLE WRAPPING INTO THE EASTERN QUADRANT AND
PERSISTENT BANDING OVER THE NORTHERN SEMI-CIRCLE. OVERALL, THE LOW-
LEVEL CIRCULATION CENTER (LLCC) HAS BECOME WELL-DEFINED WITH A
032121Z SSMIS 37 GHZ IMAGE DEPICTING A CONVECTIVE RING AND BANDING
CLEARLY WRAPPING INTO THE CENTER. TD 10W HAS ACCELERATED WESTWARD
WITHIN LOW-LEVEL ENHANCED EASTERLY FLOW BETWEEN RIDGING TO THE NORTH
AND A LARGE LOW PRESSURE AREA IN THE SOUTH CHINA SEA (CURRENTLY 99W).
B. TD 10W IS CURRENTLY TRACKING UNDER THE COMBINED STEERING INFLUENCE
OF THE LOW- TO MID-LEVEL SUBTROPICAL RIDGE POSITIONED NORTH OF THE
SYSTEM AND THE BROAD LOW PRESSURE AREA LOCATED WEST OF LUZON. ANIMAT-
ED WATER VAPOR IMAGERY INDICATES EXCELLENT POLEWARD OUTFLOW ENHANCED
BY UPPER-LEVEL LOWS LOCATED NORTHWEST OF LUZON AND SOUTH OF OKINAWA,
AND BROAD EQUATORWARD OUTFLOW. THE CURRENT POSITION IS BASED ON THE
WELL-DEFINED LLCC EVIDENT IN BOTH MULTISPECTRAL IMAGERY AND IN THE
RECENT CONVECTIVE RING SIGNATURE IN RECENT MICROWAVE IMAGERY. THERE
IS GOOD CONFIDENCE IN POSITIONING AND THE 12-HOUR STORM MOTION. THE
CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES OF 25 KNOTS FROM KNES
AND PGTW AS WELL AS ON A SHIP REPORT WITHIN 30 NM OF THE CENTER
SHOWING SOUTHWEST WINDS AT 25 KNOTS AND SLP OF 1002.2 MB.
3. FORECAST REASONING
A. THIS IS THE FIRST PROGNOSTIC REASONING.
B. TD 10W IS FORECAST TO TRACK UNDER THE STEERING INFLUENCE OF THE
LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) SITUATED TO THE NORTH
THROUGH THE FORECAST PERIOD. TD 10W IS FORECAST TO INTENSIFY AT A 20
KNOT PER DAY RATE DUE TO THE RAPID INITIAL DEVELOPMENT AND EXPECTED
FAVORABLE OUTFLOW. THIS FORECAST IS BASED ON LIMITED DYNAMIC MODEL
AIDS TO INCLUDE NOGAPS, WBAR, NCEP GFS, AND THE UK MET OFFICE. THE
MAJORITY OF THE MODELS ARE INITIALIZING THE SYSTEM POORLY, HOWEVER,
THEY ARE INITIALIZING THE LOW- TO MID-LEVEL SUBTROPICAL STEERING
RIDGE WELL AND SUPPORT A WESTWARD TRACK. MIDLATITUDE ANALYSIS ALSO
SUPPORTS THE TRACK SINCE THE PATTERN IS ZONAL AND THE STR EXTENDS
INTO EASTERN CHINA. THESE MODELS ALSO FAVOR DEVELOPMENT OF THE
SOUTH CHINA SEA CIRCULATION, WHICH APPEARS UNLIKELY AT THIS POINT
CONSIDERING THE CURRENT DEVELOPMENT OF TD 10W. THEREFORE, THERE
ARE SOME UNCERTAINTIES IN THIS INITIAL FORECAST TRACK INCLUDING THE
POSSIBILITY OF INTERACTION BETWEEN THE TWO CIRCULATIONS, WHICH
MAY INDUCE A MORE WEST-SOUTHWESTWARD TRACK IN THE EARLY TAUS UNTIL
THE SYSTEM STRENGTHENS AND RETURNS TO A WESTWARD TO WEST-NORTH-
WESTWARD TRACK. TD 10W IS FORECAST TO MAKE LANDFALL SOUTH OF HONG
KONG BY TAU 72 AND TO WEAKEN DUE TO LAND INTERACTION.
C. IN THE EXTENDED TAUS, TD 10W IS FORECAST TO CONTINUE TRACKING
WEST-NORTHWESTWARD AND TO DISSIPATE OVER LAND BY TAU 96.
FORECAST TEAM: DELTA//

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