Advisories

WDPN33 PGTW 281500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (BANG-LANG) WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.5N 166.5E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 13 NM NORTH-NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON 20W 
(BANG-LANG) WITH VERY COLD CLOUD TOPS BEGINNING TO ROTATE AROUND THE 
EXTREMELY COMPACT LOW-LEVEL CIRCULATION CENTER (LLCC), HINTING AT THE 
BEGINNING OF THE FORMATION OF AN EYE. THE LACK OF RECENT HIGH 
RESOLUTION MICROWAVE IMAGERY CAUSES THERE TO BE SOME UNCERTAINTY IN 
THE CURRENT STRUCTURE OF THE CORE. 20W MADE AN UNEXPECTED EASTWARD JOG 
OVER THE PAST 6 HOURS, PUTTING THE SYSTEM NEARLY DIRECTLY OVERHEAD OF 
WAKE ISLAND. SURFACE OBSERVATIONS ON THE ISLAND REPORTED A PRESSURE 
MINIMUM OF 985 MB WITH THE STRONGEST SUSTAINED WINDS REPORTED OF 51 
KTS FROM THE SOUTHWEST AT 281149Z. THE CENTER LIKELY PASSED JUST TO 
THE NORTH OF THE ISLAND AT AROUND 281200Z JUDGING BY THE WIND SHIFT 
FROM ESE AT 281042Z TO SW AT 281143Z. A 280957Z METOP-B ASCAT PASS 
REVEALED THAT GALE-FORCE WINDS EXTEND NO FURTHER THAN 40 NM FROM THE 
CENTER, SHOWING HOW COMPACT THE WIND FIELD IS. HOWEVER, THE RESOLUTION 
OF THE ASCAT IS TOO LOW TO ACCURATELY DEPICT THE WINDS NEAR THE CORE. 
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE 
SURFACE OBSERVATIONS FROM WAKE ISLAND AND EXTRAPOLATION FROM THE ASCAT
PASS. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH LOW CONFIDENCE 
DUE TO THE LACK OF RECENT SAR DATA AND THE AGENCY DVORAK FIXES LIKELY 
UNDERESTIMATING THE MAX INTENSITY DUE TO THE HIGHLY COMPACT NATURE OF 
THE SYSTEM. RECENT COMMUNICATIONS ISSUES HAVE CAUSED CIMSS INTENSITY 
ESTIMATES TO BE UNAVAILABLE FOR THIS WARNING, FURTHER LOWERING THE 
CONFIDENCE IN THE INITIAL INTENSITY OF 20W.

INITIAL WIND RADII BASIS: A 280957Z METOP-B ASCAT PASS AND THE 
OBJECTIVE BEST TRACK 

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: T2.5 - 35 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.0 - 45 KTS
   PHFO: T3.5 - 55 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 20W (BANG-LANG) IS FORECAST TO TRACK NORTH-
NORTHEASTWARD ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE 
(STR) CURRENTLY POSITIONED TO THE NORTHEAST THROUGH TAU 48. NEAR TAU 
48, AN INCOMING UPPER-LEVEL TROUGH IS EXPECTED TO BREAK DOWN THE 
STEERING RIDGE, PULLING 20W FURTHER POLEWARD. THE SYSTEM IS ALSO 
EXPECTED TO BEGIN INTERACTING WITH TS 21W (ETAU) STARTING AROUND TAU 
48, WHICH WILL TUG IT NORTHWESTWARD THROUGH TAU 72. SUBTROPICAL 
TRANSITION IS FORECAST TO BEGIN AROUND TAU 60 WITH COMPLETION BY TAU 
72 AS THE SYSTEM CROSSES THE 26C SST ISOTHERM AND INTERACTS WITH THE 
MIDLATITUDE THROUGH. REGARDING INTENSITY, 20W IS FORECAST TO INTENSIFY 
THROUGH TAU 24 TO A PEAK OF 85 KTS AS VERTICAL WIND SHEAR REMAINS LOW 
(LESS THAN 15 KTS) AND OCEAN HEAT CONTENT REMAINS RELATIVELY HIGH. IF 
THE SYSTEM IS ABLE TO MAINTAIN A DEFINED EYE, A HIGHER PEAK INTENSITY 
IS NOT OUTSIDE THE REALM OF POSSIBILITY. STARTING AROUND TAU 36, SHEAR 
IS EXPECTED TO INCREASE AND OCEAN HEAT CONTENT WILL RAPIDLY DROP, 
CAUSING THE SYSTEM TO WEAKEN THROUGH THE REMAINDER OF THE FORECAST 
PERIOD. 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: MODEL TRACK GUIDANCE HAS COME INTO BETTER AGREEMENT 
THIS RUN WITH THE ONLY OUTLIER BEING GALWEM, CONTINUING TO TRACK THE 
SYSTEM MUCH FURTHER WEST THAN THE REMAINDER OF GUIDANCE. DISCOUNTING 
GALWEM, THE CROSS-TRACK SPREAD AT TAU 72 IS MEASURED TO BE ABOUT 190 
NM AT TAU 72. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-
MODEL CONSENSUS WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE REMAINS IN 
POOR AGREEMENT WITH MANY RAPID INTENSIFICATION (RI) TRIGGERING. PEAK 
INTENSITIES RANGE FROM 75 KTS (GOOGLE DEEPMIND) TO 120 KTS (THE MOST 
AGGRESSIVE RI AIDS), CREATING A SIGNIFICANT SPREAD IN GUIDANCE. AS IT 
STANDS, THE JTWC INTENSITY FORECAST CONTINUES TO FOLLOW THE HAFS-A, 
CALLING FOR A PEAK OF 85 KTS WITH VERY LOW CONFIDENCE.  

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