WDPN31 PGTW 020900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (CHOI-WAN) 
WARNING NR 015//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 04W (CHOI-WAN), LOCATED APPROXIMATELY 83 
NM SOUTH-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD 
AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL 
SATELLITE IMAGERY (MSI) DEPICTS A SMALL, DISORGANIZED LOW LEVEL 
CIRCULATION CENTER (LLCC) JUST NORTHEAST OF MINDORO, WITH A RECENT 
FLARE UP OF MODERATE TO DEEP CONVECTION NOW OBSCURING THE LLCC. THE 
INITIAL POSITION IS ASSESSED WITH MODERATE CONFIDENCE BASED ON 
TRACKING OF THE LLCC IN ANIMATED VISIBLE IMAGERY BEFORE THE 
EXPANSION OF THE CONVECTIVE MASS OBSCURED IT. THE INITIAL INTENSITY 
REMAINS SET AT 30 KNOTS WITH HIGH CONFIDENCE, BASED ON AN RJTD 
DVORAK CURRENT INTENSITY ESTIMATE OF T2.0 (30 KTS), WITH ADDITIONAL 
SUPPORT PROVIDED BY A 020600Z SURFACE PRESSURE REPORT OF 1000 MB 
FROM CALAPAN, PHILIPPINES, LOCATED APPROXIMATELY 20 NM WEST OF THE 
LLCC. ENVIRONMENTAL CONDITIONS HAVE IMPROVED SLIGHTLY OVER THE PAST 
FEW HOURS, AS EVIDENCED BY THE DEVELOPMENT OF DEEP CONVECTION ONCE 
AGAIN NEAR THE CORE OF THE SYSTEM. THE UPPER-LEVEL TROUGH THAT HAS 
BEEN CLOSELY TRACKING THE LLCC IS STILL PRESENT, BUT HAS WEAKENED 
SIGNIFICANTLY, ALLOWING FOR A DECREASE IN VWS VALUES (15-20 KTS), 
AND AN INCREASE IN UPPER-LEVEL DIVERGENT EQUATORWARD OUTFLOW. TD 04W 
IS TRACKING NORTHWEST ALONG THE WESTERN PERIPHERY OF THE DEEP STR TO 
THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. OVER THE NEXT 12 HOURS, TD 04W IS FORECAST TO CONTINUE 
TRACKING NORTHWESTWARD, SKIRTING THE SOUTHERN COAST OF LUZON TO THE 
SOUTH OF MANILA AND REEMERGE INTO SOUTH CHINA SEA TO THE WEST OF 
SUBIC BAY. AS IT DOES SO, THE UPPER-LEVEL PATTERN IS EXPECTED TO 
SHIFT SLIGHTLY, WITH THE PREVIOUSLY MENTIONED TROUGH DISSIPATING, 
ALLOWING FOR DEVELOPMENT OF A DIVERGENT OUTFLOW PATTERN. THE NET 
RESULT WILL BE A SHORT PERIOD OF INTENSIFICATION, PEAKING AT 35 KTS 
THROUGH TAU 12. BY TAU 36 THE SYSTEM WILL BEGIN TO ROUND THE AXIS OF 
THE STEERING RIDGE AND WILL BEGIN TRACKING NORTHWARD INTO THE 
CONVERGENT SECTOR ON THE SOUTH SIDE OF A 200 MB ANTICYCLONE OVER 
SOUTHERN CHINA. THE CONVERGENT FLOW ALOFT WILL INHIBIT CONVECTIVE 
DEVELOPMENT AND WILL LEAD TO A STEADY WEAKENING TREND THROUGH THE 
REMAINDER OF THE FORECAST. THE SYSTEM IS EXPECTED TO DISSIPATE AS A 
TROPICAL CYCLONE BY TAU 72 AS IT EXPERIENCES RAPIDLY INCREASING VWS 
AS IT INTERACTS WITH THE STRONG MID-LATITUDE WESTERLY FLOW. DYNAMIC 
MODEL GUIDANCE IS IN GENERALLY GOOD AGREEMENT THROUGH THE DURATION 
OF THE FORECAST, WITH A MAXIMUM CROSS-TRACK SPREAD OF 110 NM AT TAU 
36 AS THE SYSTEM ROUNDS THE RIDGE AXIS. ALONG-TRACK SPREAD 
DRAMATICALLY INCREASES TO 680 NM BY TAU 72 AS THE SYSTEM ACCELERATES 
NORTHEASTWARD, WHICH IS EXPECTED IN RECURVE SCENARIOS. HOWEVER, THE 
OFFICIAL FORECAST LIES WEST OF THE GUIDANCE ENVELOPE THROUGH TAU 12 
IN LIGHT OF THE NEAR-TERM MOTION VECTOR, THEN HUGS THE WESTERN 
PORTION OF THE GUIDANCE ENVELOPE THROUGH TAU 48, THEN ON THE RIGHT 
SIDE OF THE ENVELOPE AND MUCH SLOWER THAN THE CONSENSUS MEAN THROUGH 
TAU 72. OVERALL CONFIDENCE IN THE TRACK FORECAST IS MODERATE, WITH A 
POTENTIAL TRACK FURTHER WEST THROUGH TAU 36 BEING THE PRIMARY 
ALTERNATE SCENARIO. A TRACK FURTHER WEST, OVER WARMER, HIGHER OHC 
WATERS, WOULD ALSO ALLOW FOR A LONGER PERIOD OF TIME UNDER MORE 
FAVORABLE UPPER-LEVEL CONDITIONS, ALLOWING FOR THE SYSTEM TO REACH A 
HIGHER PEAK INTENSITY BEFORE RECURVING TO THE NORTH AND BEING 
SHEARED.//
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