WDPN31 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (CHOI-WAN) 
WARNING NR 014//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 04W (CHOI-WAN), LOCATED APPROXIMATELY 
137 NM SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-
NORTHWESTWARD AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED 
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALY EXPOSED LOW-
LEVEL CIRCULATION (LLC) WITH DEEP CONVECTION BEING SHEARED TO THE 
SOUTHWEST OF THE CENTER. THE INITIAL POSITION IS PLACED WITH 
MODERATE CONFIDENCE BASED ON RADAR IMAGERY AND A 012215Z 91GHZ SSMIS 
IMAGE WHICH DEPICT EXPOSED LOW LEVEL BANDING WITH DEEP FLARING 
CONVECTION ON THE WESTERN PERIPHERY OF THE SYSTEM. THE INITIAL 
INTENSITY REMAINS AT 30 KNOTS BASED ON A SEA LEVEL PRESSURE 
OBSERVATION OF 999.6MB FROM ROMBLON (RPMR), WHICH CORRESPONDS TO 31 
KNOTS ON THE WIND-PRESSURE RELATIONSHIP TABLE. TD 04W IS CURRENTLY 
IN A MARGINALLY FAVORABLE ENVIRONMENT WITH LOW (<15 KTS) VERTICAL 
WIND SHEAR (VWS), ROBUST EQUATORWARD OUTFLOW AND WARM (30C) SSTS 
OFFSET BY CONVERGENT FLOW ALOFT DUE TO AN UPPER LEVEL TROUGH. TD 04W 
IS TRACKING ALONG THE SOUTHWEST EDGE OF A SUBTROPICAL RIDGE (STR) TO 
THE NORTH AND NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY.  
   B. TD 04W IS FORECAST TO BEGIN TURNING NORTHWESTWARD AND REACH AN 
INTENSITY OF 35KTS OVER THE SIBUYAN SEA JUST BEFORE MAKING LANDFALL 
OVER LUZON AND PASSING SLIGHTLY TO THE WEST OF MANILA. THE 
MOUNTAINOUS TERRAIN OF WESTERN LUZON WILL DISRUPT THE LOW LEVEL 
CIRCULATION, WEAKENING THE SYSTEM TO 30 KTS BY TAU 24. WHEN IT 
REEMERGES OVER WATER, THE SYSTEM WILL BE IN A LESS FAVORABLE 
ENVIRONMENT WITH MODERATE (15-25 KTS) VWS CAUSED BY UPPER-LEVEL 
EASTERLIES. THIS WEAKENING TREND WILL CONTINUE AS TD 04W BEGINS TO 
RECURVE NORTH-NORTHEASTWARD AROUND THE AXIS OF THE STR NEAR TAU 48. 
AFTER TAU 48, TD 04W TRACKS INTO THE WESTERLIES WHICH FURTHER 
WEAKENS THE SYSTEM WITH DISSIPATION BY TAU 72. THE JTWC FORECAST 
TRACK LIES SLIGHTLY WEST OF THE MULTI-MODEL CONSENSUS THROUGHOUT THE 
FORECAST PERIOD, BUT DUE TO THE UNCERTAINTY OF THE IMPACT OF THE 
LAND INTERACTION, THERE IS LOW CONFIDENCE IN BOTH THE JTWC FORECAST 
TRACK AND INTENSITY.//
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