WDPN31 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (SIX) WARNING 
NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.6N 140.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 233 NM WEST-NORTHWEST OF NAVSTA GUAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THAT
THE LOW-LEVEL CENTER (LLC) REMAINS PARTIALLY EXPOSED ON THE
SOUTHWESTERN EDGE OF A MASS OF RAGGED CONVECTION. A 221633Z AMSR2
MICROWAVE PASS SHOWED NO ORGANIZED STRUCTURE TO THE CONVECTION, AND
INDICATED A MID-LEVEL VORTEX DISPLACED ABOUT 70 NM NORTHEAST OF THE
LLC. HOWEVER, FRAGMENTED BANDING FEATURES HAVE REAPPEARED AT LARGE
RADII IN EIR SATELLITE IMAGERY DURING THE PAST 2 HOURS, AND A
RECENT CONVECTIVE BURST HAS PROPAGATED INWARD CLOSER TO THE LLC IN
THE NORTHEAST QUADRANT. UPPER-LEVEL OUTFLOW HAS IMPROVED IN ALL
QUADRANTS, THOUGH CLOUD FRAGMENTS AT AROUND THE 300MB LEVEL IN THE
SOUTHWEST QUADRANT CONTINUE TO MOVE OUT OF THE SOUTHWEST BENEATH
THE OUTFLOW TOWARD THE CIRCULATION CENTER, INDICATING THAT SOME
SOUTHWESTERLY VERTICAL SHEAR REMAINS PRESENT. ANIMATED 7.3
MICROMETER IMAGERY FROM HIMAWARI-8 SHOWS THAT THE LLC REMAINS
EMBEDDED IN A DRY LOW TO MID-LEVEL AIR MASS THAT CONTINUES TO
DOMINATE ALL BUT THE NORTHEAST QUADRANT OF THE CIRCULATION. THE
INITIAL INTENSITY IS BASED ON A SET OF THREE ASCAT SCATTEROMETER
PASSES BETWEEN 261101Z AND 261216Z.

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: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DRY LOW TO MID-LEVEL AIR MASS TO THE WEST AND
SOUTH

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 DEPRESSION (TD) 06W CONTINUES TO
TRACK NORTHWESTWARD AROUND THE PERIPHERY OF THE SUBTROPICAL RIDGE
TO THE NORTHEAST. A TURN TOWARD THE NORTH BY 48 HOURS AND THEN
NORTHEAST BY 96 HOURS IS EXPECTED AS THE CYCLONE ROUNDS THE RIDGE
AND NEARS THE BAIU FRONTAL BOUNDARY SOUTHEAST OF JAPAN,
ACCELERATING AS IT DOES SO. EVENTUAL ABSORPTION INTO THE FRONT AND
ASSOCIATED TRANSITION TO AN EXTRATROPICAL CYCLONE IS ANTICIPATED BY
120 HOURS, AIDED BY COOLING SEA SURFACE TEMPERATURES (SST) AFTER 96
HOURS. THE TIMING OF THIS TRANSITION AND THE SYSTEM'S FORWARD SPEED
DURING THE 72-120 HOUR PERIOD ARE OF ELEVATED UNCERTAINTY, WITH
ALONG-TRACK SPREAD IN MODEL GUIDANCE OF OVER 500 NM BY 120 HOURS.
THE CYCLONE'S FORWARD SPEED APPEARS TO BE SENSITIVE TO EXACTLY WHEN
IT ENTERS THE BELT OF STRONG DEEP-LAYER STEERING FLOW BETWEEN THE
SUBTROPICAL RIDGE AND THE BAIU FRONT, WHICH WILL OCCUR SOONER IF TD
06W TRACKS MORE TO THE RIGHT DURING THE NEXT 72 HOURS. THIS WILL
LARGELY DEPEND ON WHETHER THE LLC IS ABLE TO QUICKLY REALIGN
BENEATH THE MID-LEVEL CENTER THAT IS CURRENTLY DISPLACED TO THE
NORTHEAST. THE INTENSITY FORECAST ALSO DEPENDS ON THIS EVOLUTION.
VERTICAL SHEAR IS EXPECTED TO BE LOW FOR THE NEXT 24 HOURS, WHICH
COULD FACILITATE VORTEX ALIGNMENT, BUT THE AMBIENT ENVIRONMENT
REMAINS DRY, AND IS CURRENTLY PREVENTING A SYMMETRIC CONVECTIVE
STRUCTURE FROM DEVELOPING. THE JTWC INTENSITY FORECAST ASSUMES THAT
THE VORTEX WILL BE ABLE TO MIX OUT THE DRY AIR IN A LOW SHEAR
ENVIRONMENT DURING THE NEXT 36-48 HOURS, AS SUGGESTED BY THE HWRF
AND GFS MODELS, ALLOWING MODEST INTENSIFICATION DURING THE 36-72
HOUR PERIOD TO A PEAK OF AROUND 60 KT. MODERATE NORTHERLY SHEAR
AFTER 36 HOURS IS EXPECTED TO BE A LIMITING FACTOR, ESPECIALLY
GIVEN THE CYCLONE'S SMALL SIZE, WHICH MAKES IT MORE SUSCEPTIBLE TO
SHEAR. AFTER 72 HOURS, COOLER SST OF 24-25C AND PROXIMITY TO THE
BAIU FRONT IS EXPECTED TO INDUCE WEAKENING AND EXTRATROPICAL
TRANSITION BY 120 HOURS.

MODEL DISCUSSION: THE JTWC TRACK FORECAST LIES CLOSE TO THE
MULTI-MODEL CONSENSUS, BETWEEN THE LEFTWARD, SLOW ECMWF ENSEMBLE
AND THE RIGHTWARD, FAST GFS. THE JTWC INTENSITY FORECAST IS
SLIGHTLY BELOW THE MULTI-MODEL CONSENSUS THROUGH 48 HOURS, THEN
CLOSE TO CONSENSUS THEREAFTER.

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