WDPN32 PGTW 261500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 19W (NINETEEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.2N 146.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 550 NM SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A BROAD
CIRCULATION WITH PERSISTENT DEEP CONVECTION FORMING A CENTRAL DENSE
OVERCAST (CDO) FEATURE. A 261205Z ASCAT-C PASS REVEALED THE LOW
LEVEL CIRCULATION CENTER (LLCC) IS DISPLACED TO THE NORTHWESTERN
EDGE OF THE CDO FEATURE, AND REMAINS MOSTLY OBSCURED IN THE EIR AND
PROXY VISIBLE (PROXYVIS) IMAGERY. THE ACCOMPANYING AMSU-B 89GHZ
MICROWAVE IMAGE DEPICTS THE BROAD NATURE OF THE CIRCULATION WELL,
AND SHOWS THAT THE NORTHERN HEMISPHERE OF THE ROTATION IS DEVOID OF
SIGNIFICANT CONVECTION, WHILE THE DEEP CONVECTION IS ORIENTED IN A
NEAR-LINEAR BAND ALONG A NORTHWEST TO SOUTHEAST AXIS. EARLIER
SCATTEROMETER DATA SHOWED A HIGHLY ASYMMETRIC WIND FIELD, WITH
25-30 KNOT WINDS IN A BAND EXTENDING FROM SOUTHEAST TO NORTH OF THE
LLCC, WITH A RADIUS OF MAXIMUM WINDS CONTRACTING TO ABOUT 50NM. THE
STRUCTURE REVEALED BY THE SCATTEROMETERS AND MICROWAVE IMAGERY
ALIGNS WELL WITH THE MODEL DEPICTION. THE INITIAL POSITION WAS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE SCATTEROMETER DATA
ABOVE. THE INITIAL INTENSITY WAS ASSESSED WITH HIGH CONFIDENCE
BASED ON EARLIER SCATTEROMETER DATA, THE AGENCY FIXES NOTED BELOW
AND EARLY CIMSS DMINT AND DPRINT ESTIMATES OF 30 KNOTS AND 33 KNOTS
RESPECTIVELY. ANALYSIS REVEALS A MARGINAL ENVIRONMENT. WHILE THERE
APPEARS TO BE A SMALL POINT SOURCE DIRECTLY ABOVE THE SYSTEM, THERE
IS OBVIOUSLY A RELATIVELY STRONG NORTHERLY SHEAR COMPONENT
EFFECTING THE SYSTEM, WHICH IS BORN OUT BY THE GFS VORTEX AVERAGED
SKEW-T SHOWING 20 KNOTS OF SHEAR IN THE 400-850MB LEVEL. OTHERWISE,
THE PRESENCE OF TRANSVERSE BANDING IN THE EIR AND WATER VAPOR
IMAGERY CONFIRMS RADIAL OUTFLOW DIRECTLY ABOVE THE SYSTEM. SSTS ARE
VERY WARM BUT THERE IS A BIT OF DRY AIR LURKING TO THE WEST. LASTLY
THERE IS A WELL-DEFINED TUTT-CELL ABOUT 600NM TO THE NORTHEAST AND
THIS WILL HAVE A MAJOR EFFECT ON TD 19W IN THE FUTURE.

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

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS

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

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: THE PRIMARY STEERING MECHANISM FOR TD 19W FOR
THE FULL FORECAST PERIOD WILL BE THE STR SITUATED TO THE
NORTHEAST. TD 19W WILL BEGIN ROUNDING THE RIDGE AXIS BY TAU 72, AND
THEREAFTER BEGIN TO RAPIDLY ACCELERATE AS THE GRADIENT TIGHTENS
BETWEEN THE STR TO THE EAST AND A VERY STRONG UPPER-LEVEL TROUGH
WHICH MOVES INTO OVER JAPAN. BY TAU 96, TD 19W WILL BE MOVING AT
NEARLY 20 KNOTS TO THE NORTHEAST AND CONTINUING TO ACCELERATE. BY
THE END OF THE FORECAST PERIOD THE SYSTEM IS EXPECTED TO BE EAST OF
NORTHERN HONSHU AND MOVING QUICKLY INTO THE OPEN WATERS OF THE
NORTHWEST PACIFIC. IN TERMS OF INTENSITY, THE MAIN DRIVERS WILL BE
DRY MID-LEVEL AIR, SHEAR AND THE TUTT-CELL. FIRSTLY, THE DRY AIR
THAT IS CURRENTLY LURKING TO THE WEST OF TD 19W IS EXPECTED TO
REMAIN FIRMLY IN PLACE FOR THE FIRST 48 TO 60 HOURS OF THE
FORECAST. SECONDLY, DEEP-LAYER SHEAR, WHILE CURRENTLY LOW, IS
FORECAST TO PICK UP TO MODERATE TO HIGH LEVELS FOR ROUGHLY THE SAME
TIME PERIOD. LASTLY, THE TUTT-CELL TO THE NORTHEAST IS FORECAST TO
MOVE WESTWARD WHILE TD 19W MOVES NORTHWESTWARD, SUCH THAT THE TWO
COME ALMOST IN ALIGNMENT BY TAU 48. THIS WILL PLACE TD 19W TO THE
SOUTHWEST AND SOUTH OF THE TUTT-CELL, IN AN UNFAVORABLE POSITION
WITH CONVERGENT FLOW ALOFT. THE COMBINATION OF FACTORS MEANS THAT
WHILE THERE MAY BE A VERY SHORT WINDOW OF OPPORTUNITY FOR A SLIGHT
AMOUNT OF INTENSIFICATION IN THE NEAR-TERM, THAT WILL BE IT FOR A
WHILE. THE FORECAST CALLS FOR STEADY INTENSITY THROUGH TAU 48 BUT
IT IS POSSIBLE THAT THE SYSTEM COULD WEAKEN SLIGHTLY DURING THE
FIRST 48 HOURS OF THE FORECAST. HOWEVER, BY TAU 72 THINGS START TO
LOOK UP. THE ATMOSPHERE IS EXPECTED TO MOISTEN UP, SHEAR DROPS OFF
CONSIDERABLY, AND MOST IMPORTANTLY THE TUTT-CELL SLIDES WEST OF THE
SYSTEM, INTO A FAVORABLE POSITION. BY TAU 72, OUTFLOW BUILDS INTO
THE BASE OF THE APPROACHING 200MB TROUGH, ALLOWING FOR THE SYSTEM
TO INTENSIFY UP TO A PEAK OF 55 KNOTS BY TAU 96. THE MAIN LIMITING
FACTOR IN THE POTENTIAL INTENSITY WILL BE THE RELATIVELY LARGE RMW
AND ASYMMETRIC WIND FIELD, WHICH WILL HINDER RAPID INTENSIFICATION
IN AN OTHERWISE FAVORABLE ENVIRONMENT. BY TAU 120, THE SYSTEM WILL
BE IN THE THROWS OF EXTRATROPICAL TRANSITION (ETT) AS IT MOVES INTO
THE BAROCLINIC ZONE AND UNDER A 200MB JET MAX.   

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN FAIRLY GOOD
AGREEMENT, WITH ALL MODELS INDICATING A RECURVE SCENARIO. AS
EXPECTED IN A RECURVE EVENT, THERE IS A MODEST AMOUNT OF
CROSS-TRACK SPREAD, WHICH INCREASES AS THE SYSTEM APPROACHES THE
RIDGE AXIS, WITH THE GUIDANCE PACKAGE SPREAD OUT ACROSS 330NM WITH
GFS ON THE EASTERN SIDE AND EGRR ON THE WESTERN. AFTER TAU 72,
CROSS-TRACK SPREAD REMAINS RELATIVELY CONSISTENT, BUT ALONG-TRACK
SPREAD INCREASES DRAMATICALLY, WITH THE GFS LEADING THE PACK RACING
THE SYSTEM AT A BLISTERING 35 KNOTS TO THE NORTHEAST, WHILE THE
SLOWER JGSM LAGS BEHIND BY 750NM. ENSEMBLE MEMBERS (GEFS AND ECENS)
ARE IN GOOD AGREEMENT THROUGH TAU 72, BUT SPREAD OUT AFTER AS THE
SYSTEM ROUNDS THE RIDGE. THE MAJORITY OF THE MEMBERS REMAIN
OFFSHORE JAPAN, THOUGH APPROXIMATELY 10 PERCENT DO TRACK OVER FAR
EASTERN JAPAN EAST OF TOKYO. THE JTWC FORECAST TRACKS CLOSE TO THE
CONSENSUS THROUGH TAU 72 WITH HIGH CONFIDENCE. AFTER TAU 72,
CONFIDENCE IS REDUCED DUE TO THE INCREASED ALONG-TRACK SPREAD, WITH
THE JTWC FORECAST ROUGHLY IN LINE WITH BUT FASTER THAN THE
CONSENSUS MEAN. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE
SYSTEM WILL REACH 35 KNOTS IN THE NEAR-TERM, THEN REMAIN STEADY,
FOLLOWED BY INTENSIFICATION AFTER TAU 60. THE HAFS-A IS THE MOST
AGGRESSIVE, PEAKING NEAR TYPHOON STRENGTH, WHILE THE COAMPS-TC
(GFS) IS THE WEAKEST, PEAKING AT JUST 45 KNOTS. THE JTWC FORECAST
LIES ON THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD WITH MEDIUM
CONFIDENCE. 

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