WDPN31 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING 
NR 02//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 04W, LOCATED APPROXIMATELY 290 NM EAST 
OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 13 KNOTS OVER 
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY 
INDICATES A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC) WITH 
IMPROVED CONVECTIVE BANDING WRAPPING INTO WELL-DEFINED LLCC. 
CONSEQUENTLY, THE 01/00Z DVORAK INTENSITY ESTIMATES HAVE INCREASED 
TO T2.0 (30 KNOTS) SUPPORTING THE CURRENT INTENSITY ASSESSMENT OF 30 
KNOTS. A 010005Z SSMIS IMAGE DEPICTS IMPROVED DEEP CONVECTIVE 
BANDING SURROUNDING THE CENTER. UPPER-LEVEL ANALYSIS INDICATES A 
FAVORABLE ENVIRONMENT CHARACTERIZED BY WEAK VERTICAL WIND SHEAR 
(VWS) AND EXCELLENT, NEARLY RADIAL OUTFLOW ENHANCED BY A TUTT CELL 
NEAR GUAM AND AN ANTICYCLONE IN THE SOUTHERN HEMISPHERE.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TD 04W IS CURRENTLY TRACKING ALONG THE SOUTHWEST PERIPHERY OF 
THE LOW-LEVEL SUBTROPICAL RIDGE, WHICH EXTENDS WESTWARD TO TAIWAN 
FROM A STRONG PERSISTENT HIGH NEAR 30N 170W. THE 31/12Z 500 MB 
ANALYSIS INDICATES THAT THE DOMINANT STEERING INFLUENCE IS THE 
EASTERN SUBTROPICAL RIDGE (STR). THIS ANALYSIS ALSO SHOWS THAT THE 
WESTERN STR HAS RETROGRADED WESTWARD (WEST OF HONG KONG) DUE TO 
PREVAILING WESTERLY FLOW EXTENDING OVER THE EAST CHINA SEA AND 
TAIWAN. THIS SYNOPTIC PATTERN IS FORECAST TO REMAIN STATIC THROUGH 
THE FORECAST PERIOD WITH A MIDLATITUDE SHORTWAVE TROUGH FORECAST TO 
DEEPEN OVER THE EAST CHINA SEA NEAR TAU 72. THEREFORE, THERE IS HIGH 
CONFIDENCE IN THE SHARP RE-CURVE SCENARIO WITH A LOW PROBABILITY OF 
A TRACK INTO THE SOUTH CHINA SEA. AVAILABLE MODEL GUIDANCE IS IN 
TIGHT AGREEMENT WITH THE EXCEPTION OF THE INTERPOLATED UKMO TRACKER, 
WHICH TRACKS MORE NORTHWARD NEAR OKINAWA. THIS NORTHWARD TRACK AFTER 
TAU 72 IS AN ARTIFICE OF THE INTERPOLATOR CODE AND DOESN'T FIT WITH 
THE UKMO ENSEMBLE SOLUTIONS, WHICH ARE PREDOMINANTLY EAST OF THE 
UKMO TRACKER SOLUTION REFLECTING A SHARP TURN DUE TO THE WESTERLY 
FLOW. THIS FORECAST IS POSITIONED CLOSE TO THE MODEL CONSENSUS 
THROUGH TAU 72. TD 04W IS FORECAST TO INTENSIFY TO A PEAK INTENSITY 
OF 85 KNOTS BY TAU 72.
   C. IN THE EXTENDED PERIOD, TD 04W IS EXPECTED TO ROUND THE 
NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE AND BEGIN TO 
INTERACT WITH MIDLATITUDE WESTERLY FLOW. THEREFORE, THE SYSTEM WILL 
BEGIN TO WEAKEN AND TRACK OVER COOLER SST (LESS THAN 25C) WHILE 
BEGINNING EXTRA-TROPICAL TRANSITION (ETT) NEAR TAU 96. THE SYSTEM IS 
EXPECTED TO COMPLETE ETT AFTER TAU 120 AS IT BECOMES EMBEDDED WITHIN 
THE BAROCLINIC ZONE WELL SOUTH OF JAPAN AND ACCELERATES EASTWARD. 
THERE IS HIGH CONFIDENCE IN THIS PORTION OF THE TRACK DUE TO THE 
RELATIVELY ZONAL WESTERLY JET FORECAST BY ALL THE DYNAMIC MODELS TO 
REMAIN ENTRENCHED OVER (AND WELL SOUTH OF) JAPAN. ADDITIONALLY, THE 
SYSTEM SHOULD TRACK EAST OF OKINAWA BUT MAY PRODUCE INCREASED WINDS 
AS THE EXTREME NORTHWESTERN PERIPHERY OF THE SYSTEM INTERACTS WITH A 
DEVELOPING MIDLATITUDE HIGH.//
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