Advisories

WDPN33 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 19W (NINETEEN) 
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.7N 136.5E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 473 NM WEST OF NAVSTA GUAM
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A NEARLY
FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH
TROPICAL DEPRESSION (TD) 19W (NINETEEN). THE CONVECTIVE STRUCTURE IS
HIGHLY ASYMMETRIC, WITH MOST OF THE DEEP CONVECTION CONFINED TO THE
WESTERN SEMICIRCLE, AS ALSO REFLECTED IN THE WIND FIELD OBSERVED IN
A PARTIAL 231204Z METOP-C ASCAT PASS. THE LOW-LEVEL VORTEX IS EMBEDDED 
WITHIN A STRONG STEERING ENVIRONMENT AND IS SUBJECT TO 10-15 KTS OF 
NORTHEASTERLY VERTICAL WIND SHEAR (VWS). ENVIRONMENTAL CONDITIONS 
REMAIN MARGINAL, WITH WARM (29-30 C) SEA SURFACE TEMPERATURES (SST) 
AND A MODERATE EQUATORWARD OUTFLOW CHANNEL. ALTHOUGH TROPOSPHERIC 
MOISTURE REMAINS RELATIVELY HIGH ALONG THE WESTERN PERIPHERY, 
METEOROLOGICAL ANALYSIS INDICATES THE SYSTEM IS BEING CONSTRAINED BY 
DRY AIR TO THE EAST AND NORTHEAST. THE INITIAL POSITION IS ASSESSED 
WITH HIGH CONFIDENCE BASED ON THE NEARLY FULLY EXPOSED LLCC OBSERVED 
IN THE SHORTWAVE INFRARED LOOP. THE INITIAL INTENSITY OF 30 KTS IS 
ALSO ASSESSED WITH HIGH CONFIDENCE, PRIMARILY BASED ON THE PARTIAL 
231204Z METOP-C ASCAT PASS SHOWING 25-30 KTS, WHICH IS CONSISTENT WITH 
THE AUTOMATED AND AGENCY INTENSITY 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 ADT: 35 KTS AT 231210Z
   CIMSS AIDT: 32 KTS AT 231210Z
   CIMSS D-PRINT: 27 KTS AT 231210Z

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

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 MOVING NORTHEASTWARD UNDER THE COMBINED 
INFLUENCE OF A NEAR-EQUATORIAL RIDGE (NER) POSITIONED TO THE EAST-
SOUTHEAST AND LOW-LEVEL SOUTHWESTERLY FLOW. BY TAU 24, THE SYSTEM IS 
FORECAST TO TRANSITION TO A NEW STEERING PATTERN DOMINATED BY A 
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST, WHICH WILL TURN TD 19W 
NORTHWARD AND THEN NORTHWESTWARD IN THE WAKE OF TYPHOON 17W (SAUDEL). 
NUMERICAL MODEL GUIDANCE INDICATES THAT THE VWS WILL INCREASE TO 25-30 
KTS BY AROUND TAU 12. THIS INCREASE IN SHEAR, COMBINED WITH DRY-AIR 
ENTRAINMENT, WILL SUPPORT A STEADY WEAKENING TREND, WITH WINDS 
DECREASING TO 20-25 KTS BY TAU 36. BY TAU 48, TD 19W WILL LIKELY 
STRUGGLE TO MAINTAIN VERTICAL COHERENCE AS IT ENCOUNTERS THE HIGHLY 
SHEARED PERIPHERAL FLOW ASSOCIATED WITH TYPHOON 17W. CONSEQUENTLY,
DISSIPATION OVER WATER IS FORECAST BY TAU 48, THOUGH A FASTER RATE OF 
WEAKENING IS POSSIBLE SHOULD VERTICAL WIND SHEAR AND DRY MID-LEVEL 
ADVECTION BE STRONGER THAN CURRENTLY FORECAST.

MODEL DISCUSSION: NUMERICAL TRACK GUIDANCE IS IN MODERATE AGREEMENT 
THROUGHOUT THE CURRENT FORECAST PERIOD, WITH A CROSS-TRACK SPREAD OF 
ABOUT 95 NM AT TAU 48, BUT AN ALONG-TRACK SPREAD OF MORE THAN 200 NM. 
THE OFFICIAL JTWC TRACK FORECAST IS POSITIONED CLOSE TO THE MULTI-
MODEL CONSENSUS. UKMET AND GFS ARE THE PRIMARY OUTLIERS, REPRESENTING 
THE SLOWEST AND FASTEST SOLUTIONS, RESPECTIVELY. INTENSITY GUIDANCE IS 
GENERALLY IN GOOD AGREEMENT ON A WEAKENING TREND, ESPECIALLY AFTER TAU 
24, WITH COAMPS-TC THE PRIMARY OUTLIER IN FORECASTING INTENSIFICATION 
TO 50-55 KTS. THEREFORE, THE OFFICIAL JTWC INTENSITY FORECAST IS 
PLACED NEAR THE HIGHER END OF THE GUIDANCE ENVELOPE, BUT REMAINS CLOSE 
TO THE MULTI-MODEL CONSENSUS, WITH MEDIUM CONFIDENCE.

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