Advisories

WDPN31 PGTW 032100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 046//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.8N 138.7E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 154 NM WEST-SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 30W UNDERWENT SIGNIFICANT CONSOLIDATION BETWEEN 0600Z
AND 1800Z, WITH A RING OF -60 TO -65 DEGREES CELSIUS CLOUD-TOP
TEMPERATURES ENCIRCLING A RAGGED 30-NM-WIDE EYE. A 031214Z ASCAT-C
UHR PASS ESTIMATED MAXIMUM WINDS NEAR 80 KTS. BASED ON THESE DATA
AND THE IMPROVED CONVECTIVE SIGNATURE, THE 1200Z BEST TRACK
INTENSITY WAS REANALYZED TO 80 KTS. SINCE THEN, THE WESTERN SIDE OF
THE INNER CORE ERODED SOMEWHAT DUE TO 20-25 KTS OF WESTERLY
MID-LEVEL SHEAR. AN EARLIER 030757Z SSMIS 91 GHZ IMAGE SUPPORTED
THIS ASSESSMENT, SHOWING EASTWARD VORTEX TILT WITH HEIGHT. DEEP
CONVECTION HAS BEEN WRAPPING UPSHEAR ACROSS THE WESTERN PERIPHERY
OF THE CIRCULATION, IMPROVING THE OVERALL CONVECTIVE STRUCTURE. IN
THE MOST RECENT ENHANCED INFRARED (EIR) IMAGERY, THE STRUCTURE NOW
APPEARS SIMILAR TO THAT AT 1200Z. THE ENVIRONMENT IS MARGINALLY
FAVORABLE, WITH SEA SURFACE TEMPERATURES (SST) OF 27-28 DEGREES
CELSIUS AND STRONG POLEWARD OUTFLOW, OFFSET BY MODERATE TO HIGH
VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON THE RAGGED, PARTIALLY CLEAR EYE. THE
INITIAL INTENSITY HAS BEEN SET AT 85 KTS WITH MEDIUM CONFIDENCE,
WHICH IS ON THE HIGHER END OF THE OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: 1200Z SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF THE DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR 25N 154E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 92 KTS AT 031800Z
   CIMSS ADT: 84 KTS AT 031800Z
   CIMSS AIDT: 72 KTS AT 031800Z
   CIMSS D-MINT: 76 KTS AT 031640Z
   CIMSS D-PRINT: 84 KTS AT 031800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 30W HAS TURNED SHARPLY POLEWARD AS IT
ROUNDS THE WESTERN PERIPHERY OF THE STR. THE SYSTEM WILL CROSS THE
RIDGE AXIS NEAR TAU 12 AND THEN BEGIN TO TURN EASTWARD. AS THIS
HAPPENS, A PROGRESSIVE LONGWAVE TROUGH PASSING OVER THE KOREAN
PENINSULA AND HONSHU WILL CAUSE THE SYSTEM TO ACCELERATE
NORTHEASTWARD AND BECOME EMBEDDED IN THE MID-LATITUDE DEEP-LAYER
SOUTHWESTERLY FLOW. VWS WILL INCREASE THROUGH THE FORECAST PERIOD,
REACHING 30 KTS BY TAU 12 AND 40 KTS BY TAU 24. VERY HIGH SHEAR
WILL THEN PERSIST AS THE SYSTEM TRACKS BENEATH THE SOUTHERN
PERIPHERY OF THE JET STREAM. SST WILL PROGRESSIVELY COOL AS TY 30W
GAINS LATITUDE, DECREASING BELOW 26 DEGREES CELSIUS BY TAU 36. THE
STRONG POLEWARD OUTFLOW CHANNEL WILL BECOME INCREASINGLY UNABLE TO
OVERCOME THESE DETRIMENTAL ENVIRONMENTAL EFFECTS, BUT INCREASING
BAROCLINIC INSTABILITY SHOULD OFFSET SOME OF THE WEAKENING. STRONG
THERMAL ADVECTION, ROBUST UPPER-LEVEL SUPPORT, AND INCREASING
FORWARD SPEED AFTER TAU 48 SHOULD LEAD TO BAROCLINIC
REINTENSIFICATION OF THE COMPACT SYSTEM AS IT RAPIDLY UNDERGOES
EXTRATROPICAL TRANSITION (ETT). ETT SHOULD COMPLETE BY TAU 60.

MODEL DISCUSSION: TRACK GUIDANCE EXHIBITS A SMALL CROSS-TRACK
SPREAD BUT A VERY LARGE ALONG-TRACK SPREAD OF 615 NM AT TAU 60. THE
CROSS-TRACK SPREAD MODESTLY WIDENS AT TAU 60, BUT A CORE GROUP
CONSISTING OF GOOGLE DEEPMIND, UKMET, AND ECMWF OCCUPY THE NORTHERN
SIDE OF THE GUIDANCE ENVELOPE. THE GREATEST DISPARITY EXISTS IN THE
TRACK SPEED. NAVGEM AND GALWEM ARE AMONG THE SLOWEST MODELS, WHILE
DEEPMIND IS THE FASTEST. TRACK GUIDANCE HAS GENERALLY SHIFTED
SLIGHTLY WESTWARD THIS CYCLE. THE JTWC FORECAST TRACK IS POSITIONED
ALONG THE EASTERN SIDE OF THE TIGHT GUIDANCE ENVELOPE, CLOSEST TO
DEEPMIND, THROUGH TAU 48. BY TAU 60, THE JTWC FORECAST SHIFTS
TOWARD THE AI-MODEL MEAN. HAFS-A IS AN INTENSITY OUTLIER, DEPICTING
INTENSIFICATION TO 100 KTS BY TAU 24. EXCLUDING HAFS-A, THE
INTENSITY GUIDANCE LARGELY DEPICTS A STEADY INTENSITY THROUGH TAU
12, FOLLOWED BY GRADUAL TO STEADY WEAKENING UNTIL TAU 48. FROM TAU
48 TO TAU 60, DEEPMIND KEEPS THE INTENSITY FLAT, WHILE GFS AND
ECMWF BRING THE SYSTEM UP TO 70 KTS. THE JTWC INTENSITY FORECAST IS
SET NEAR THE DEEPMIND SOLUTION THROUGH TAU 48 AND NEAR THE GFS AND
ECMWF SOLUTION AT TAU 60.

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