Advisories

WDPN33 PGTW 230900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 19W (NINETEEN) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.4N 135.9E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 267 NM NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH TROPICAL 
DEPRESSION (TD) 19W (NINETEEN) ACCELERATING NORTHEASTWARD. DEEP 
CONVECTION HAS BEEN DISPLACED TO THE SOUTHWEST AS A RESULT OF STRONG 
GRADIENT FLOW IN WHICH THE LLCC IS CURRENTLY EMBEDDED, MULTIPLIED BY 
10-15 KT VERTICAL WIND SHEAR (VWS) FROM THE NORTHEAST. ADDITIONAL 
ENVIRONMENTAL ANALYSIS REVEALS MARGINAL CONDITIONS FOR FURTHER 
DEVELOPMENT. SEA SURFACE TEMPERATURES (SST) REMAIN WARM (29-30 C) AND 
OUTFLOW IS ENHANCED BY A MODERATE EQUATORWARD CHANNEL. WHILE 
PERSISTENT TROPOSPHERIC MOISTURE IS HIGHLY CONCENTRATED WITHIN THE 
WESTERN QUADRANT, SIGNIFICANT DRY-AIR INTRUSION EMBEDDED TO THE EAST 
AND NORTHEAST CONTINUES TO ENVELOPE THE SYSTEM. STRUCTURALLY, TD 19W 
IS BECOMING MORE ELONGATED AS WITNESSED BY 230420Z GW1 AMSR2 MICROWAVE 
IMAGERY AND SUPPORTED BY AN EARLIER (230057Z) METOP-C ASCAT PASS. THE 
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON VISIBLE 
IMAGERY OF THE FULLY EXPOSED LLCC. THE INITIAL INTENSITY OF 30 KTS IS 
ALSO ASSESSED WITH HIGH CONFIDENCE BASED ON A 230230Z OSCAT PASS, AND
THE AUTOMATED AND AGENCY ESTIMATES LISTED BELOW.

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

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) TO THE
SOUTHEAST AND LOW-LEVEL SOUTHWESTERLIES

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 39 KTS AT 230610Z
   CIMSS ADT: 34 KTS AT 230610Z
   CIMSS AIDT: 31 KTS AT 230610Z
   CIMSS D-MINT: 27 KTS AT 230500Z
   CIMSS D-PRINT: 31 KTS AT 230640Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT THROUGHOUT THE EASTERN
SEMICIRCLE

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: TD 19W IS CURRENTLY ACCELERATING NORTHEASTWARD, 
DRIVEN BY THE STEERING INFLUENCE OF A NER ANCHORED TO THE EAST-
SOUTHEAST AND ENHANCED BY LOW-LEVEL SOUTHWESTERLIES. AROUND TAU 24, 
THE DOMINANT STEERING INFLUENCE WILL SHIFT TO A SUBTROPICAL RIDGE 
POSITIONED TO THE NORTHEAST, VEERING TD 19W NORTHWARD AND 
NORTHWESTWARD ALONG THE SUBSIDED WAKE OF TYPHOON 17W (SAUDEL). WHILE 
THE VWS IS EXPECTED TO REMAIN INITIALLY LOW, MODEL GUIDANCE INDICATES 
SIGNIFICANT UPTICK JUST PRIOR TO TAU 24, WHICH COMBINED WITH 
INCREASING ENTRAINMENT OF DRY AIR INTO THE CORE WILL INITIATE A 
WEAKENING TREND, DEPRESSING INTENSITY TO 20-25 KTS BY TAU 36. TOWARDS 
TAU 48, TD 19W WILL STRUGGLE TO PRESERVE ITS VERTICAL STRUCTURE AS IT 
ENTERS THE REGION OF SHEARED TAIL END WINDS OF TYPHOON 17W. 
ACCORDINGLY, COMPLETE DISSIPATION OVER OPEN WATER IS PROJECTED BY TAU 
48, ALTHOUGH AN ACCELERATED DECAY TIMELINE REMAINS VIABLE SHOULD 
INCREASED VERTICAL WIND SHEAR AND DRY AIR ADVECTION BE MORE PRONOUNCED 
AS CURRENTLY MODELED.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE EXHIBITS FAIR INITIAL
CONSISTENCY, EVIDENCED BY A CONSTRAINED 115 NM CROSS-TRACK SPREAD AT 
TAU 48, WITH ALL MAJOR GLOBAL AND MESOSCALE SYSTEMS RESOLVING COHERENT 
MOTION UNDER CURRENT STEERING FORCING. WHILE THE OFFICIAL JTWC TRACK 
IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS, CURRENT PLACEMENT IS 
LEANING TOWARDS THE WESTERN PROJECTION OF THE EXPERIMENTAL GOOGLE 
DEEPMIND GUIDANCE, WHICH HAS BEEN INITIALIZING VERY WELL OVER THE LAST 
48 HOURS. IN TERMS OF INTENSITY, GFS DEPICTS A LIGHT INCREASE IN PEAK 
WIND SPEEDS TO 35 KTS AT TAU 12, FOLLOWED BY WEAKENING AND EVENTUAL 
DECAY. ALL OTHER CONSENSUS MEMBERS PREDICT STEADY WEAKENING, WITH HAFS 
ESTIMATING FULL DISSIPATION AS EARLY AS TAU 24. THE ONLY OUTLIER IS A 
GFS-DRIVEN COAMPS-TC, WHICH ESTIMATES THE SYSTEM REACHING 45-50 KTS 
AROUND TAU 24. OFFICIAL JTWC INTENSITY FORECAST IS LAID CLOSE TO THE
MULTI-MODEL CONSENSUS AND SLIGHTLY ABOVE WIND SPEED MAXIMA PROPOSED BY 
HAFS GUIDANCE, WITH MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM//
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