WDPN31 PGTW 212100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (SIX) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.6N 144.5E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 46 NM SOUTH-SOUTHWEST OF HAGATNA, GUAM
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY AND DOPPLER
RADAR IMAGERY FROM GUAM DEPICT A SHEARED CYCLONE, WITH A COMPACT
LOW-LEVEL CENTER (LLC) LOCATED NEAR THE SOUTHWESTERN EDGE OF A MASS
OF RAGGED CONVECTION. A TUTT CELL TO THE WEST CAN BE SEEN PUSHING
CIRRUS FRAGMENTS TOWARD THE LLC FROM THE SOUTHWEST, DENOTING
MODERATE SOUTHWESTERLY SHEAR. DRY MID-LEVEL AIR ASSOCIATED WITH THE
TUTT CELL IS CURRENTLY PREVENTING UPSHEAR PROPAGATION OF
CONVECTION, EVIDENCED BY THE IMMEDIATE EVAPORATION OF NASCENT
THUNDERSTORMS IN THE WESTERN SEMICIRCLE DURING THE PAST 6 HOURS.
THE INITIAL POSITION AND INTENSITY ARE BOTH LARGELY BASED ON RADAR
IMAGERY, WHICH HAS SHOWN A WELL-DEFINED VORTEX CONTAINING
WIDESPREAD 35-40 KT DOPPLER VELOCITIES AT 4000-7000 FT, TRANSLATING
ROUGHLY TO 30 KT SURFACE WINDS. A 211549Z AMSR2 PASS ALSO SUPPORTED
MAXIMUM SURFACE WINDS OF 25-30 KT. OVERALL ORGANIZATION OF THE
VORTEX HAS CHANGED LITTLE DURING THE PAST 6 HOURS.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 36 KTS AT 210903Z
   CIMSS ADT: 33 KTS AT 211430Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK EASTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 DEPRESSION (TD) 06W WILL CONTINUE
TRACKING NORTHWESTWARD AROUND THE SOUTHWESTERN PERIPHERY OF A
DEEP-LAYER SUBTROPICAL RIDGE TO THE NORTHEAST, EVENTUALLY TURNING
NORTHWARD BY 72 HOURS. THE SPEED WITH WHICH TD 06W ROUNDS THIS
RIDGE WILL DEPEND ON HOW FAR NORTHEAST THE CYCLONE TRACKS DURING
THE NEXT 48-72 HOURS, AS A MORE RIGHTWARD TRACK WOULD PLACE THE
CYCLONE CLOSER TO THE STRONG BELT OF DEEP-LAYER SOUTHERLY FLOW,
LEADING TO FASTER FORWARD MOTION. NUMERICAL MODEL GUIDANCE IS THUS
SPREAD BETWEEN SLOWER, LEFTWARD TRACKS AND FASTER, RIGHTWARD
TRACKS. THE JTWC TRACK FORECAST LEANS SLIGHTLY TOWARD THE
RIGHT-HAND SIDE OF THE GUIDANCE ENVELOPE DURING THE FIRST 72 HOURS,
IN PART DUE TO A SLIGHT JOG NORTH OF GUIDANCE DURING THE PAST 12
HOURS. THE JTWC TRACK FORECAST IS ALSO A BIT SLOWER DURING THE
72-120 HOUR PERIOD COMPARED TO THE PREVIOUS FORECAST, FOLLOWING THE
RECENT GUIDANCE TREND. THE LARGE-SCALE ENVIRONMENT IS EXPECTED TO
REMAIN ONLY MARGINALLY FAVORABLE FOR INTENSIFICATION, AS CONTINUED
ENTANGLEMENT WITH THE NEARBY UPPER-LEVEL TROUGH WILL RESULT IN
MODERATE SHEAR FOR THE NEXT 12-24 HOURS AND A SOMEWHAT DRY
SURROUNDING AIR MASS. SHEAR IS EXPECTED TO LESSEN DURING THE 24-48
HOUR PERIOD AS THE UPPER-LEVEL TROUGH WEAKENS, AND MODEST
INTENSIFICATION TO A PEAK OF 50 KT IS FORECAST BY 72 HOURS. SHEAR
IS THEN EXPECTED TO INCREASE AGAIN, AS WHILE THE CYCLONE WILL BE
PASSING BENEATH AN UPPER-LEVEL RIDGE AXIS, STRONG LOW-MID LEVEL
SOUTHERLY FLOW BETWEEN THE SUBTROPICAL RIDGE AND MEI-YU FRONTAL
BOUNDARY WILL RESULT IN MODERATE NORTHERLY SHEAR. TD 06W IS THUS
EXPECTED TO WEAKEN GRADUALLY AFTER 72 HOURS, THEN MORE STEADILY TO
35 KT BY 120 HOURS AS THE CYCLONE CROSSES INTO COOLER SEA SURFACE
TEMPERATURES OF 24-25C. GIVEN THE SMALL SIZE OF THE CYCLONE THAT IS
FORECAST TO PERSIST, POTENTIAL INTERACTION WITH THE MEI-YU BOUNDARY
INDUCES LOWER CONFIDENCE IN THE TRACK FORECAST AFTER 72 HOURS.

MODEL DISCUSSION: THE JTWC TRACK FORECAST GENERALLY LIES SLIGHTLY
TO THE RIGHT AND SLOWER THAN THE MULTI-MODEL CONSENSUS, IN PART DUE
TO THE LEFTWARD OUTLIERS AFUM AND UKMET ENSEMBLE WHICH DO NOT
PROPERLY RESOLVE THE SMALL TROPICAL CYCLONE VORTEX, AS WELL AS THE
SPEEDY OUTLIER NAVGEM. THE JTWC INTENSITY FORECAST IS SLIGHTLY
BELOW THE MULTI-MODEL CONSENSUS AFTER 48 HOURS.

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