WDPN33 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (KRATHON) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.7N 124.3E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 311 NM NORTHEAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TS 20W
KRATHON TRACKING WEST-NORTHWESTWARD, WHILE DEVELOPING SPIRAL BANDS
OF DEEP CONVECTION ALL AROUND, AS WELL AS MODERATE RADIAL OUTFLOW.
WHILE THE SUBTROPICAL RIDGE (STR) TO THE EAST OF THE SYSTEM REMAINS
THE DOMINANT STEERING MECHANISM, THE COMPETING INFLUENCE FROM THE STR
TO THE NORTHWEST IS IMPACTING THE TRACK OF THE SYSTEM, MAKING IT 
SLIGHTLY MORE WESTWARD. THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON A 281913Z SSMIS 91GHZ MICROWAVE EYE, AS WELL AS A 
282206Z WSFM 37GHZ MICROWAVE PASS SHOWING THE POSITIONAL PROGRESSION 
OF THE LLCC. THE INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE AGENCY DVORAK AND AUTOMATED FIXES LISTED
BELOW, CONSISTENT WITH A FORMATIVE EYE IN THE EIR LOOP.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: TWO COMPETING STEERING FEATURES IN A
FORM OF SUBTROPICAL RIDGES TO THE NORTHWEST AND TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 56 KTS AT 281530Z
   CIMSS ADT: 61 KTS AT 290130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM KRATHON IS FORECAST TO CONTINUE 
TRACKING WEST-NORTHWESTWARD UNTIL THE STR TO THE NORTHEAST WEAKENS, 
AND KRATHON BEGINS NORTHERLY TURN BY TAU 48, FOLLOWED BY NORTHEASTWARD 
TURN BY TAU 72. IT IS FORECAST TO CONTINUE INTENSIFYING, IMMINENTLY 
REACHING TYPHOON SPEEDS AND REACHING A PEAK INTENSITY OF 100 KTS AT 
TAUS 48-72 AS JET INTENSITY WINDS AHEAD OF AN UPPER LEVEL TROUGH WEST 
OF JAPAN WILL ENHANCE THE POLEWARD OUTFLOW. THE SYSTEM WILL THEN 
CONTINUE ALONG THE COASTLINE OF TAIWAN, WHILE STEADILY WEAKENING DUE 
TO LAND INTERACTION WITH TAIWAN, UPPER-LEVEL TROUGHING TO THE NORTH-
NORTHEAST, AND DRY COLD AIR INTRUSION FROM THE SAME DIRECTION COMBINED 
WITH INCREASING VERTICAL WIND SHEAR.
 
MODEL DISCUSSION: MOST RECENT NUMERICAL MODEL GUIDANCE RUNS ARE IN
TIGHTER AGREEMENT THAN LAST FORECAST, SUGGESTING THE TRACK TO
ALMOST BRUSH THE SOUTHERN TIP OF TAIWAN. JTWC TRACK IS LAID CLOSE
TO THE MULTI MODEL CONSENSUS AND BETWEEN THE GUIDELINES FROM ECMFW
AND GFS ENSEMBLES. THE WEAKENING TIMELINE OF THE STR TO THE
NORTHWEST WILL ULTIMATELY DETERMINE IF THE TRACK OF 20W REACHES
TAIWAN OR IF THE SYSTEM MAKES THE TURN JUST PRIOR TO THE APPROACH.
THE CURRENT CROSS-TRACK SPREAD AT TAU IS 81 NM, WHILE THE SPREAD
BETWEEN ECMWF AND GFS ENSEMBLE IS 42 NM. ALONG-TRACK SPREAD IS
CURRENTLY 40 NM INDICATING IMPROVING AGREEMENT ACROSS THE MODELS.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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