WDPN31 PGTW 252100
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: 22.4N 145.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 249 NM SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL DEPRESSION (TD) 19W HAS SLOWLY CONSOLIDATED OVER THE PAST
12 HOURS AROUND A BROAD LOW-LEVEL CIRCULATION (LLC). ALTHOUGH A
251200Z ASCAT-B IMAGE SHOWED A SHARP TROUGH WITH NO CLOSED
CIRCULATION, ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
DEPICTS IMPROVED CONVECTIVE BANDING ALONG THE SOUTHERN AND EASTERN
PERIPHERIES. CONSEQUENTLY, DVORAK ESTIMATES HAVE INCREASED TO T1.5 
(25 KNOTS) FROM ALL AGENCIES. THE ASCAT-B IMAGE INDICATED A SWATH OF 
30-35 KNOT WINDS ASSOCIATED WITH THE CONVECTIVE BANDING BUT LESS THAN 
20 KNOTS ELSEWHERE THUS THE INITIAL INTENSITY IS ASSESSED SLIGHTLY 
HIGHER THAN THE DVORAK INTENSITY ESTIMATES. THE 251157Z ASCAT-B 
WINDSPEED IMAGE SHOWS A WIND MINIMUM SUGGESTING A DEVELOPING LOW-
LEVEL CIRCULATION CENTER AND A 251640Z ATMS 88.2GHZ MICROWAVE IMAGE 
SHOWS A WEAKLY-DEFINED LLCC ALONG THE WESTERN EDGE OF THE CURVED 
BAND, WHICH SUPPORTS THE INITIAL POSITION WITH MEDIUM CONFIDENCE.

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

CURRENT STEERING MECHANISM: COMBINED STEERING INFLUENCE WITH A DEEP-
LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST AND A WEAK STR 
TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TD 19W IS FORECAST TO TRACK GENERALLY
NORTHWESTWARD THROUGH TAU 24 WITHIN THE COMBINED STEERING INFLUENCE
OF THE BROAD STR TO THE EAST AND THE WEAK STR POSITIONED TO THE
NORTH. AFTER TAU 24, A DEEP MIDLATITUDE SHORTWAVE TROUGH WILL
APPROACH CENTRAL JAPAN AND WEAKEN THE STR TO THE NORTH ALLOWING THE 
SYSTEM TO TURN POLEWARD THROUGH TAU 36 THEN RECURVE NORTHEASTWARD 
ALONG THE NORTHWESTERN FLANK OF THE RE-ORIENTED STR TO THE SOUTHEAST. 
BY TAU 48, TD 19W WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS IT 
INTERACTS WITH THE MIDLATITUDE WESTERLIES AND BAROCLINIC ZONE. THE 
SYSTEM WILL COMPLETE ETT BY TAU 72 AS IT GAINS FRONTAL 
CHARACTERISTICS AND BECOMES EMBEDDED WITHIN THE MIDLATITUDE 
WESTERLIES. TD 19W SHOULD INTENSIFY STEADILY THROUGH TAU 48 UNDER 
FAVORABLE CONDITIONS TO A PEAK OF 70 KNOTS. AFTER TAU 48, COOLER SEA 
SURFACE TEMPERATURE VALUES (25-26C) AND STRONG VERTICAL WIND SHEAR 
WILL WEAKEN THE SYSTEM.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
WITH A SPREAD OF LESS THAN 80NM THROUGH THE FORECAST PERIOD LENDING
HIGH CONFIDENCE TO THE JTWC FORECAST TRACK. ADDITIONALLY, THE
250600Z ECMWF ENSEMBLE (EPS) AND 251200Z GFS ENSEMBLE (GEFS) ARE IN
GOOD AGREEMENT SUPPORTING THE JTWC FORECAST TRACK. THE 251200Z
COAMPS-TC ENSEMBLE INDICATES A LOW PROBABILITY (10 TO 30 PERCENT)
FOR RAPID INTENSIFICATION PEAKING IN THE TAU 36 TO TAU 60 PERIOD.  

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