Advisories

WDPN33 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (BANG-LANG) WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.2N 167.8E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 187 NM NORTH-NORTHEAST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
20W (BANG-LANG) WITH COLLAPSING DEEP CONVECTION AND QUICKLY WARMING
CLOUD TOPS. THE 282226Z ASCAT PASS REVEALS A HIGHLY ASYMMETRIC WIND
FIELD, WITH CALM (5-10 KTS) WINDS DOMINATING THE WESTERN HEMISPHERE
AND THE TYPHOON-FORCE WINDS CONFINED TO A VERY SMALL POCKET IN THE
SOUTHEASTERN QUADRANT. IN ADDITION TO ASYMMETRY WITHIN THE WIND
SPEEDS, THE ASCAT ALSO REVEALED A PRONOUNCED ASYMMETRY WITH LOWER
LEVEL STRUCTURE. THE WINDS WITHIN NORTHWESTERN QUADRANT APPEAR TO
BE POORLY WRAPPED INTO THE CORE OF 20W, INDICATIVE BINARY
INTERACTION WITH TROPICAL STORM (TS) 21W HAS BEGUN AND THOSE WINDS
ARE BEING PULLED BETWEEN THE TWO SYSTEMS. ENVIRONMENTAL ANALYSIS
REVEALS A MARGINALLY FAVORABLE ENVIRONMENT, CHARACTERIZED BY LOW TO
MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS), GOOD OUTFLOW ALOFT,
AND WARM (28-29 C) SEA SURFACE TEMPERATURES, BUT OFFSET BY SLIGHT
DRY AIR ENTRAINMENT AND MARGINAL OCEAN HEAT CONTENT. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON EXTRAPOLATION FROM
THE 282226Z ASCAT AMBIGUITY PRODUCT. THE INITIAL INTENSITY OF 65
KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE 282226Z ASCAT
WIND SPEED PRODUCT.

INITIAL WIND RADII BASIS: ADJUSTED WIND RADII USING THE 282226Z
ASCAT DATA

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T4.0 - 65 KTS
   PHFO: T4.0 - 65 KTS
   CIMSS ADT: 63 KTS AT 290010Z
   CIMSS AIDT: 50 KTS AT 290010Z
   CIMSS D-MINT: 67 KTS AT 282210Z
   CIMSS D-PRINT: 61 KTS AT 282340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: MODERATE MID-LEVEL DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

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 12-24
HOURS. AROUND TAU 12, 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 48. ADDITIONALLY, 20W HAS BEGUN
INTERACTING WITH TROPICAL STORM (TS) 21W (ETAU), WITH INTERACTION
GETTING STRONGER AS THE TWO STORMS ARE PULLED CLOSER TOGETHER. THIS
INTERACTION WILL REINFORCE THE NORTH-NORTHWEST TRACK MOTION AND
CAUSE A CURVE BACK TO THE NORTH AFTER TAU 48. 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 48 AND
COMPLETE TRANSITION NO LATER THAN TAU 60. BY TAU 60, 20W IS
FORECAST TO HAVE CROSSED THE 26C ISOTHERM AND BE FULLY EMBEDDED
UNDER THE UPPER-LEVEL TROUGH. REGARDING INTENSITY, 20W IS FORECAST
TO INTENSIFY THROUGH TAU 12-24 AS THE ENVIRONMENT REMAINS
MARGINALLY FAVORABLE. STARTING AROUND TAU 12-24, SHEAR IS EXPECTED
TO INCREASE AS THE UPPER-LEVEL TROUGH PASSES, INDUCING ADDITIONAL
DRY AIR ENTRAINMENT. CONCURRENTLY, 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 36. AFTER TAU 36, 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 -- THOUGH IMPROVING -- AGREEMENT
WITH A FEW RAPID INTENSIFICATION (RI) AIDS STILL TRIGGERING. PEAK
INTENSITIES RANGE FROM 65-80 KTS (HAFS-A, HWRF, COAMPS-TC, GFS, AND
EXPERIMENTAL GOOGLE DEEPMIND) TO 100 KTS (THE MOST AGGRESSIVE RI
AIDS), CREATING A SIGNIFICANT SPREAD IN INTENSITY GUIDANCE.
HOWEVER, MOST AIDS AGREE ON A PEAK IN ABOUT 12 HOURS. THE JTWC
INTENSITY FORECAST CONTINUES TO HEDGE CLOSER TO THE HAFS-A, HWRF,
AND COAMPS-TC SOLUTIONS WITH VERY LOW CONFIDENCE.

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