WDPS31 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 31P (THIRTYONE)    
WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.6S 139.5E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 504 NM EAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A PARTIALLY-
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) POSITIONED ALONG THE 
NORTHWESTERN EDGE OF THE CONVECTIVE MASS. ALTHOUGH THE LLCC IS LOCATED 
ABOUT 140NM WEST OF THE WEIPA RADAR, ANIMATED RADAR IMAGERY SHOWS A 
FAINT REFLECTION OF THE LLCC, WITH WEAK BANDING WRAPPING INTO THE LLCC 
AND CONVECTIVE BANDING OVER THE EASTERN AND SOUTHEASTERN QUADRANTS. A 
201603Z AMSR2 WINDSPEED IMAGE SHOWS NO DISTINCT CENTER BUT DOES SHOW AN 
ASYMMETRIC WINDFIELD, WITH A SWATH OF 25-30 KNOT WINDS OVER THE 
SOUTHEAST QUADRANT ASSOCIATED WITH THE PRIMARY CONVECTIVE BAND. 
ENVIRONMENTAL CONDITIONS HAVE IMPROVED SLIGHTLY, WITH IMPROVED POLEWARD 
OUTFLOW. HOWEVER, THE VORTEX REMAINS TILTED AND THERE IS EVIDENCE OF 
MID- TO UPPER-LEVEL DRY AIR ENTRAINMENT, WHICH ARE HINDERING SIGNIFICANT 
DEVELOPMENT. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE AMSR2 DATA.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   ADRM: T2.5 - 35 KTS
   CIMSS SATCON: 39 KTS AT 201630Z
   CIMSS ADT: 43 KTS AT 201730Z
   CIMSS AIDT: 35 KTS AT 201730Z
   CIMSS D-PRINT: 28 KTS AT 201730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT, VORTEX TILT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 31P IS FORECAST TO TRACK 
WESTWARD TO WEST-NORTHWESTWARD ALONG THE NORTHERN PERIPHERY OF THE STR 
THROUGH THE FORECAST PERIOD. TC 31P HAS CONTINUED TO STRUGGLE TO 
ORGANIZE BUT IS STILL EXPECTED TO INTENSIFY SLIGHTLY WITHIN THE NEXT 12 
HOURS AS IT TRACKS OVER WARM WATER AND MOISTENS GRADUALLY. HAFS-A AND 
GFS INDICATE THE GRADUAL MOISTENING OF THE CORE AND A MORE FAVORABLE 
VERTICAL ALIGNMENT THROUGH TAU 48, WHICH WILL ALLOW THE SYSTEM TO 
SUSTAIN MINIMAL TROPICAL STORM STRENGTH NEAR 35 KNOTS. AFTER TAU 48, TC 
31P WILL GRADUALLY WEAKEN DUE TO DRY AIR ENTRAINMENT AND INCREASING MID-
LEVEL VERTICAL WIND SHEAR, WITH DISSIPATION ANTICIPATED BY TAU 72. 

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, WHICH DRIVES THE SYSTEM 
SOUTHWARD INTO THE STR, DETERMINISTIC MODEL GUIDANCE REMAINS IN FAIR 
AGREEMENT SUPPORTING THE JTWC TRACK FORECAST WITH MEDIUM CONFIDENCE. THE 
201200Z ECENS AND GEFS RUNS ALSO SHOW A TIGHT GROUPING OF SOLUTIONS 
THROUGH TAU 72, WITH A HIGH PROBABILITY OF A 30-40 KNOT SYSTEM. RELIABLE 
INTENSITY GUIDANCE REVEALS A LARGE SPREAD, WITH COAMPS-TC (GFS) AND GFS 
SHOWING A PEAK INTENSITY OF 33 KNOTS WHILE HAFS-A INDICATES A SLIGHTLY 
HIGHER PEAK OF 41 KNOTS AT TAU 72. ALTHOUGH THE SYSTEM IS NOT EXPECTED 
TO BRING MAJOR IMPACTS TO THE DARWIN AREA, ENHANCED GRADIENT WINDS MAY 
OCCUR AS THE SYSTEM PASSES NORTH OF DARWIN IN TWO TO THREE DAYS.  

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