WDPN31 PGTW 191500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (SIXTEEN) 
WARNING NR 029//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.4N 132.9E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 562 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TD 16W (SIXTEEN) HAS REGENERATED AS A TROPICAL DEPRESSION IN THE
PHILIPPINE SEA. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
SHOWS THAT DEEP CONVECTION BEGAN DEVELOPING ONCE MORE OVER THE LOW
LEVEL CIRCULATION CENTER (LLCC) AT APPROXIMATELY 190600Z, AND HAS
PERSISTED THROUGH THE 191200Z HOUR. CLOUD TOP TEMPS HAVE COOLED
SIGNIFICANTLY, AND HIGH RESOLUTION IMAGERY DEPICTS THE DEVELOPMENT
OF SOME OVERSHOOTING TOPS, INDICATING THE SYSTEM IS UNDERGOING
INTENSIFICATION. WHILE THE CONVECTION SIGNATURE IS VERY
SYMMETRICAL, THE OVERALL SURFACE WIND FIELD IS HIGHLY ASYMMETRICAL,
AS CONFIRMED BY A PARTIAL 191218Z ASCAT-B PASS, WHICH SHOWED 15-20
KNOT WINDS ON THE NORTH-NORTHWEST SIDE OF THE SYSTEM. EARLIER
SCATTEROMETER DATA SHOWED 25-30 KNOT WINDS CONFINED TO AN AREA
EXTENDING FROM THE NORTHEAST-SOUTH OF THE LLCC. THE INITIAL
POSITION IS ASSESSED WITH LOW CONFIDENCE DUE TO AN OBSCURED LLCC
AND THE LACK OF RECENT MICROWAVE IMAGERY AND SCATTEROMETER DATA.
THE INITIAL INTENSITY IS HEDGED SLIGHTLY HIGHER THAN THE
MULTI-AGENCY INTENSITY ESTIMATES OF T1.0 IN LIGHT OF THE IMPROVED
STRUCTURE AND CONVECTIVE DEVELOPMENT. EARLIER IN THE DAY, MODERATE
TO STRONG WESTERLY SHEAR WAS INHIBITING THE DEVELOPMENT OF THE
CONVECTIVE CORE, HOWEVER OVER THE PAST 12 HOURS THE UPPER-LEVEL
PATTERN HAS MODIFIED, WITH A ANTICYCLONE DEVELOPING OVER TOP OF TD
16W, LEADING TO MUCH LOWER SHEAR AND WEAK RADIAL OUTFLOW, WITH THE
REMNANTS OF A WEAK TUTT CELL TO THE NORTH PROVIDING A VERY WEAK TAP
INTO SOME POLEWARD OUTFLOW AS WELL. A DEEP, SHARP, MID-LATITUDE
TROUGH EXTENDS SOUTHWARD FROM THE KOREAN PENINSULA, ALONG THE
RYUKYU CHAIN, TO THE LUZON STRAIT.

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

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF DEEP
SUBTROPICAL RIDGE (STR) CENTERED EAST OF JAPAN. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T1.0 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS IS THE INITIAL PROGNOSTIC
REASONING MESSAGE AFTER REGENERATION AND ESTABLISHES THE FORECAST
PHILOSOPHY.

FORECAST DISCUSSION: TD 16W WILL CONTINUE TO TRACK NORTHWEST ALONG
THE SOUTHWEST PERIPHERY OF THE DEEP STR THROUGH TAU 48, THEN TURN
NORTH BY TAU 72 AS IT APPROACHES A BREAK IN THE STR, THEN
ACCELERATE NORTH-NORTHEASTWARD THROUGH THE REMAINDER OF THE
FORECAST ALONG THE GRADIENT BETWEEN THE STR AND A MID-LATITUDE
TROUGH APPROACHING FROM THE WEST. AS THE UPPER-LEVEL ANTI-CYCLONE
ALOFT TRACKS ALONG WITH THE LLCC, PROVIDING A SOURCE OF WEAK RADIAL
OUTFLOW ALOFT AND RELATIVELY LOW VWS, THE SYSTEM IS FORECAST TO
STEADILY INTENSIFY AT THE CLIMATOLOGICAL RATE OF ROUGHLY ONE
T-NUMBER PER DAY, PEAKING AT 40 KNOTS BY TAU 48. WHILE OVERALL
INTENSITY IS EXPECTED TO STEADILY INCREASE, THE LOW-LEVEL WIND
FIELD IS FORECAST TO REMAIN ASYMMETRIC, WITH THE HIGHEST WINDS
CONFINED TO THE EASTERN HEMISPHERE OF THE SYSTEM. THE SHARP TROUGH
CURRENTLY NEAR THE RYUKYUS IS NOT EXPECTED TO MOVE MUCH FURTHER TO
THE SOUTH OR EAST BUT THE STRONG NORTHEASTERLY FLOW BEHIND IT WILL
SERVE AS A WALL UPON WHICH TD 16W WILL ULTIMATELY MEET ITS DEMISE.
BETWEEN TAU 48 AND 72, TD 16W WILL MOVE UNDER THESE STRONG
NORTHEASTERLY WINDS ALOFT, EXPERIENCE DRAMATICALLY INCREASED VWS
AND CONVERGENCE ALOFT, LEADING TO FAIRLY RAPID DISSIPATION NO LATER
THAN TAU 96. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN MODEST AGREEMENT ON THE
RECURVE SCENARIO, WITH CROSS-TRACK SPREAD BEING THE MAJOR
CONTRIBUTOR TO UNCERTAINTY THROUGH TAU 72, AND ALONG-TRACK SPREAD
THEREAFTER AS THE SYSTEM ACCELERATES NORTHEASTWARD AFTER RECURVING.
THE UKMET ENSEMBLE IS THE LEFT OUTLIER WHILE ECMWF IS THE RIGHT
OUTLIER, WITH A CROSS-TRACK SPREAD OF 160 NM AT TAU 48. AFTER
CROSSING THE RIDGE AXIS, GFS AND THE GFS ENSEMBLE ACCELERATE THE
SYSTEM EXCESSIVELY FAST, WHILE THE UKMET ENSEMBLE DOES NOT SHOW A
RECURVE, LEADING TO A SPREAD OF 630 NM AT TAU 96. THE JTWC TRACK
LIES ON THE LEFT EDGE OF GUIDANCE ENVELOPE THROUGH TAU 72, THEN
JUST AHEAD OF THE MULTI-MODEL CONSENSUS MEAN BY TAU 96. INTENSITY
GUIDANCE HAS COME INTO MUCH BETTER AGREEMENT WITH THIS RUN, WITH
THE MAJORITY OF MESOSCALE MODELS SUPPORTING THE JTWC FORECAST,
WHICH LIES CLOSE TO THE CONSENSUS MEAN THROUGH TAU 48, THEN WEAKENS
THE SYSTEM FASTER THAN THE MEAN THROUGH TAU 96. OVERALL CONFIDENCE
IN THE TRACK IS MEDIUM TRENDING TO LOW AFTER TAU 72. CONFIDENCE IN
THE INTENSITY IS MEDIUM IN THE NEAR-TERM, TRENDING TO HIGH
THEREAFTER.

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