WDPN31 PGTW 172100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (ONE) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 01W (ONE), LOCATED APPROXIMATELY 422 NM 
EAST OF DAVAO, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 05 
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE 
IMAGERY REVEALS AN EXPOSED, DEFINED LOW-LEVEL CIRCULATION CENTER 
(LLCC) ON THE SOUTHEAST EDGE OF AN AREA OF FLARING DEEP CONVECTION.  
A 171705Z AMSR2 89GHZ COLOR COMPOSITE IMAGE INDICATES SHALLOW 
BANDING WRAPPING TIGHTLY INTO THE DEFINED LLCC WITH RAGGED, 
FORMATIVE BANDING DISPLACED OVER THE NORTHERN SEMICIRCLE. OVERALL, 
THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION BASED PRIMARILY ON 
THE AMSR2 MICROWAVE IMAGE. THE INITIAL INTENSITY REMAINS ASSESSED AT 
30 KNOTS, HEDGED ABOVE PGTW/RJTD DVORAK ESTIMATES OF T1.5 (25 
KNOTS), BASED ON A 171840Z ADT ESTIMATE OF 2.2 (32 KNOTS). UPPER-
LEVEL ANALYSIS INDICATES A MARGINALLY-FAVORABLE ENVIRONMENT WITH 
MODERATE (20 KNOTS) EASTERLY VERTICAL WIND SHEAR (VWS) OFFSET BY 
DIFFLUENT EASTERLY FLOW AND ROBUST POLEWARD OUTFLOW. SST VALUES 
REMAIN CONDUCIVE AT 29-30C. TD 01W IS TRACKING ALONG THE SOUTHWEST 
PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO 
THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE IN THE FORECAST PHILOSOPHY FROM 
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TD 01W IS LOCATED WITHIN A WEAK STEERING ENVIRONMENT SOUTH OF 
A BREAK IN THE SUBTROPICAL RIDGE (STR) ASSOCIATED WITH A MAJOR 
SHORTWAVE TROUGH CURRENTLY OVER AND SOUTH OF JAPAN. IN GENERAL, THE 
SYSTEM WILL TRACK SLOWLY WESTWARD TO WEST-NORTHWESTWARD THROUGH TAU 
48 UNTIL THE MAJOR TROUGH SHIFTS EASTWARD AND ZONAL FLOW 
PREDOMINATES. THIS WILL ALLOW THE STR TO RE-BUILD NORTHEAST AND 
NORTH OF THE SYSTEM, WHICH WILL ALLOW THE SYSTEM TO ACCELERATE WEST-
NORTHWESTWARD WITH LANDFALL OCCURRING NEAR TAU 72. NUMERICAL MODEL 
GUIDANCE IS IN FAIR AGREEMENT WITH A 175NM SPREAD IN SOLUTIONS AT 
TAU 72. TD 01W WILL INTENSIFY STEADILY TO A PEAK INTENSITY OF 60 
KNOTS BY TAU 48 UNDER GENERALLY FAVORABLE CONDITIONS, ESPECIALLY 
STRONG POLEWARD OUTFLOW. HOWEVER, THERE IS SOME UNCERTAINTY IN THE 
PEAK INTENSITY DUE TO THE PERSISTENT MODERATE VWS.    
   C. AFTER TAU 72, TD 01W WILL TRACK ACROSS THE PHILIPPINE 
ARCHIPELAGO, AND BY TAU 120, WILL REACH THE SOUTH CHINA SEA OFF THE 
ISLAND OF MINDORO. INTERACTION WITH THE ISLANDS AND INCREASED VWS 
WILL WEAKEN THE SYSTEM DOWN TO 35 KNOTS BY TAU 120. NUMERICAL MODEL 
GUIDANCE DIVERGES AND IS POOR AGREEMENT IN THE EXTENDED PERIOD WITH 
A LARGE SPREAD OF 480NM AT TAU 120. SEVERAL MODELS (NAVGEM, UKMET 
DETERMINISTIC AND UKMET ENSEMBLE MEAN) ARE RECURVING THE SYSTEM 
NORTHWESTWARD, WHICH IS UNLIKELY DUE TO THE STRONG LIKELIHOOD OF A 
RE-BUILDING STR AND ZONAL UPPER-LEVEL FLOW OVER THE EAST CHINA SEA. 
OVERALL, THERE IS FAIR CONFIDENCE IN THE JTWC FORECAST TRACK, WHICH 
IS POSITIONED NEAR THE MULTI-MODEL CONSENSUS.//
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