Advisories

WDPN33 PGTW 290900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (BANG-LANG) WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.9N 168.2E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 290 NM NORTH-NORTHEAST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS OVERSHOOTING
TOPS WRAPPING AROUND THE CENTER OF A WELL-DEFINED CENTRAL DENSE
OVERCAST (CDO), WITH THE EYE ATTEMPTING TO CLEAR OUT. TYPHOON 20W
HAS INTENSIFIED OVER THE PAST 12 HOURS, A TREND VISIBLY MANIFESTED
IN THE RECENT 89 GHZ AND 37 GHZ MICROWAVE IMAGERY, BEGINNING WITH
THE 281858Z WSF-M MWI PASS, FOLLOWED BY AMSR3 AT 290044Z, AMSR2 AT
290206Z, AND SSMIS AT 290437Z. EACH PASS SHOWED GRADUAL IMPROVEMENT
IN THE CONVECTIVE STRUCTURE AND A MORE CONSOLIDATED INNER CORE. THE
UPPER-LEVEL DIVERGENCE IS STILL HEALTHY, AS THE MSI DEPICTS RADIAL
OUTFLOW ALOFT. THIS SYSTEM IS TINY AND HAS A STRONGLY ASYMMETRIC
WIND FIELD, WITH GALE-FORCE WINDS EXTENDING APPROXIMATELY 70 NM OUT
FROM THE CENTER IN THE NORTHEAST QUADRANT. THE ENVIRONMENT IS STILL
FAVORABLE, CHARACTERIZED BY WARM SEA SURFACE TEMPERATURE (SST)
OFFSET BY A SLIGHT MID-LEVEL INTRUSION OF DRY AIR, AND MODERATE
VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE DIMPLE AT THE CENTER OF THE CDO. BASED
ON THE IMPROVED CONVECTIVE SIGNATURE, THE INITIAL INTENSITY HAS
BEEN RAISED TO 75 KTS WITH MEDIUM CONFIDENCE. WHILE THIS ASSESSMENT
IS ABOVE ALL OF THE OBJECTIVE INTENSITY ESTIMATES FROM CIMSS, IT
AGREES WITH THE HIGHER SIDE OF THE SUBJECTIVE DVORAK ESTIMATES,
PARTICULARLY WITH THE DATA T-NUMBER OF 4.5 FROM THE EMBEDDED CENTER
TECHNIQUE.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE CENTERED OVER THE DATELINE

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   PHFO: T4.5 - 77 KTS
   CIMSS SATCON: 60 KTS AT 290530Z
   CIMSS ADT: 55 KTS AT 290600Z
   CIMSS AIDT: 52 KTS AT 290600Z
   CIMSS D-MINT: 69 KTS AT 290437Z
   CIMSS D-PRINT: 65 KTS AT 290600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 20W WILL ACCELERATE POLEWARD OVER THE NEXT
12-24 HOURS UNDER THE STEERING INFLUENCE OF A STR POSITION TO THE
EAST. FROM TAU 12 TO TAU 36, THE TRACK WILL SLIGHTLY DEVIATE TOWARD
THE NORTH-NORTHWEST AS THE SYSTEM BRIEFLY INTERACTS WITH TROPICAL
STORM (TS) 21W. IT WILL RESUME A MORE POLEWARD TRAJECTORY AFTER TAU
36, BEFORE TURNING NORTH-NORTHEASTWARD AS THE STR WEAKENS AND
ALLOWS THE MID-LATITUDE WESTERLIES TO EXERT MORE OF AN INFLUENCE.
TY 20W IS LIKELY AT OR NEAR PEAK INTENSITY. THE CIRCULATION IS
BEGINNING TO TRAVERSE OVER A COLD WAKE LEFT BEHIND BY TS 21W. THE
COOLER SST OF 27-28 DEGREES CELSIUS WILL STILL BE SUFFICIENTLY WARM
TO MAINTAIN THE INTENSITY FOR THE NEXT 12 HOURS. BY TAU 24, THE
SYSTEM WILL APPROACH THE 26 DEGREE CELSIUS ISOTHERM AND ENTER A
DRIER AIR MASS, WHICH WILL INITIATE A WEAKENING TREND. THE OCEAN
WATERS AHEAD ARE EVEN COOLER, AND THE VWS WILL INCREASE. THIS WILL
LEAD TO STEADY TO RAPID WEAKENING FOR THE REMAINDER OF THE FORECAST
PERIOD, WITH THE SYSTEM TRANSITIONING TO A SUBTROPICAL STORM BY TAU
60.

MODEL DISCUSSION: MODELS ARE IN FAIR AGREEMENT, DEPICTING A MOSTLY
POLEWARD TRACK THROUGH TAU 60. THE CROSS-TRACK SPREAD IS LOW AT 100
NM AT TAU 48, BUT THE ALONG-TRACK SPREAD IS LESS THAN IDEAL AT 175
NM. THE JTWC FORECAST TRACK LEANS WITH MEDIUM CONFIDENCE TOWARD THE
AI CONSENSUS, WHICH HAS BEEN OUTPERFORMING MANY OF THE
PHYSICS-BASED SOLUTIONS. THE HAFS-A AND GFS MODELS DEPICT SLOW
WEAKENING FOR THE FIRST 12 HOURS, FOLLOWED BY MORE RAPID DECAY. THE
EXPERIMENTAL GOOGLE DEEPMIND SOLUTION LOSES THE CIRCULATION AFTER
12 HOURS. THE JTWC INTENSITY FORECAST AGREES WITH THIS PHILOSOPHY
AND IS SET NEAR THE HAFS-A SOLUTION WITH MEDIUM CONFIDENCE.

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