Advisories

WDPN33 PGTW 282100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (BANG-LANG) WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5N 167.0E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 75 NM NORTH-NORTHEAST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 20W (BANG-LANG) WITH QUICKLY WARMING CLOUD TOPS AND COLLAPSING
DEEP CONVECTION WITHIN THE CENTRAL DENSE OVERCAST (CDO). FOR A
BRIEF MOMENT, IT APPEARED AS IF 20W WAS ATTEMPTING TO FORM AN EYE,
HOWEVER, THE CONVECTION WARMED AND THE ATTEMPT WAS ABANDONED. THE
281723Z SSMIS DATA REVEALS A VERY SLIGHT PATCH OF LOWER EMISSIVITY
IN THE CENTER OF THE CDO REGION, BUT IT REMAINS FAR FROM A DEFINED
MICROWAVE EYE. ENVIRONMENTAL ANALYSIS REVEALS A FAVORABLE
ENVIRONMENT, CHARACTERIZED BY LOW (10-15 KTS) VERTICAL WIND SHEAR
(VWS), WARM (29-30 C) SEA SURFACE TEMPERATURES (SST), GOOD OUTFLOW
ALOFT. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED
ON THE AFOREMENTIONED 281723Z SSMIS MICROWAVE DATA. THE INITIAL
INTENSITY OF 65 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK FIXES AND CIMSS AUTOMATED INTENSITY ESTIMATES LISTED
BELOW, WITH A SLIGHT BIAS CORRECTION APPLIED TO THE INITIAL
INTENSITY. THE DVORAK FIXES ARE ASSESSED TO BE SLIGHTLY
UNDER-ESTIMATING THE INTENSITY DUE TO THE VERY COMPACT NATURE OF
THE STORM.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTWARD EXTENSION OF A
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   PHFO: T3.5 - 55 KTS
   CIMSS SATCON: 64 KTS AT 281910Z
   CIMSS ADT: 63 KTS AT 281910Z
   CIMSS AIDT: 53 KTS AT 281910Z
   CIMSS D-MINT: 47 KTS AT 281722Z
   CIMSS D-PRINT: 59 KTS AT 281830Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TY 20W (BANG-LANG) IS FORECAST TO CONTINUE
TRACKING NORTH-NORTHEASTWARD  WHILE IT REMAINS UNDER THE STEERING
INFLUENCE OF THE STR CENTERED TO ITS NORTHEAST FOR THE NEXT 24-36
HOURS. AROUND TAU 36, AN UPPER-LEVEL TROUGH IS EXPECTED TO PASS TO
THE NORTH AND WEAKEN THE RIDGE, INDUCING A NORTH-NORTHWESTWARD
TRACK MOTION FOR 20W THROUGH TAU 60. ALSO BEGINNING AROUND TAU 36,
20W IS EXPECTED TO BEGIN TO INTERACT WITH TROPICAL STORM (TS) 21W
(ETAU), REINFORCING THE NORTH-NORTHWEST TRACK MOTION. INTERACTION
WITH TS 21W MAY RESULT IN STORM MOTION NOT REFLECTED IN THE
OFFICIAL FORECAST, AS THE DEGREE OF INTERACTION IS STILL UNCERTAIN.
TY 20W IS EXPECTED TO BEGIN SUBTROPICAL TRANSITION (STT) AROUND TAU
60 AND COMPLETE TRANSITION NO LATER THAN TAU 72. BY TAU 72, 20W IS
FORECAST TO HAVE CROSSED THE 26C ISOTHERM AND BE EMBEDDED UNDER THE
UPPER-LEVEL TROUGH. REGARDING INTENSITY, 20W IS FORECAST TO
INTENSIFY THROUGH TAU 24 TO A PEAK OF 85 KTS AS THE ENVIRONMENT
REMAINS FAVORABLE. IF 20W IS ABLE TO SUCCESSFULLY FORM AN EYE, A
HIGHER PEAK INTENSITY IS POSSIBLE. STARTING AROUND TAU 36, SHEAR IS
EXPECTED TO INCREASE AS THE UPPER-LEVEL TROUGH PASSES AND OCEAN
HEAT CONTENT WILL RAPIDLY DROP AS THE SYSTEM PROGRESSES POLEWARD.
AS A RESULT, BANG-LANG IS FORECAST TO GRADUALLY WEAKEN FROM TAU
24-72. THE HIGHLY COMPACT NATURE OF THE SYSTEM MAY CAUSE THE
INTENSITY TO BE VOLATILE AS SMALL CHANGES IN THE ENVIRONMENT COULD
HAVE A LARGE IMPACT ON THE VORTEX.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 48, WITH THE ONLY OUTLIER BEING GALWEM. AFTER
TAU 48, GUIDANCE DIVERGES QUITE A BIT AS THE BINARY INTERACTION
BETWEEN 20W AND 21W BECOMES MORE PRONOUNCED AND MODEL GUIDANCE
STRUGGLES TO INITIALIZE IT. AS A RESULT, THE JTWC TRACK FORECAST
IS PLACED WITH LOW CONFIDENCE. INTENSITY GUIDANCE REMAINS IN POOR
AGREEMENT WITH MANY RAPID INTENSIFICATION (RI) AIDS REACHING
CRITERIA. PEAK INTENSITIES RANGE FROM 70-75 KTS (HAFS-A, COAMPS-TC,
AND GFS) TO 135 KTS (THE MOST AGGRESSIVE RI AIDS), CREATING A VERY
SIGNIFICANT SPREAD IN INTENSITY GUIDANCE. THE JTWC INTENSITY
FORECAST CONTINUES TO HEDGE CLOSER TO THE HAFS-A, GFS, AND
COAMPS-TC SOLUTIONS WITH VERY LOW CONFIDENCE.  

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