Advisories

WDPN31 PGTW 040900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 048//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.0N 138.3E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 164 NM WEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 30W
(IN-FA) WITH A SIGNIFICANTLY EASTWARD-TILTED VORTEX WITH HEIGHT DUE
TO MODERATE TO HIGH WESTERLY VERTICAL WIND SHEAR. THE OVERALL
STRUCTURE OF 30W HAS DEGRADED OVER THE PAST 6 HOURS WITH A HIGHLY
RAGGED EYE THAT IS NEARLY FILLED. ADDITIONALLY, THE LOW-LEVEL
CIRCULATION CENTER (LLCC) HAS BECOME PARTIALLY EXPOSED ON THE
WESTERN SIDE. A 040333Z AMSR3 MICROWAVE IMAGE SUITE CONFIRMED THE
TILTED NATURE OF THE VORTEX AND THE 37 GHZ IMAGE REVEALED THAT THE
WESTERN PORTION OF THE MICROWAVE EYE HAS ALMOST COMPLETELY ERODED.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
PARTIALLY-EXPOSED LLCC IN THE ANIMATED MSI AND EXTRAPOLATION FROM
THE AMSR3 IMAGE. THE INITIAL INTENSITY OF 80 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE T4.5 AGENCY DVORAK FIXES AND THE
CIMSS INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE FROM THE 040022Z METOP-B
ASCAT PASS WITH MINOR ADJUSTMENTS BASED ON THE OBJECTIVE BEST TRACK

CURRENT STEERING MECHANISM: THE WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS ADT: 92 KTS AT 040600Z
   CIMSS AIDT: 83 KTS AT 040600Z
   CIMSS D-MINT: 78 KTS AT 040451Z
   CIMSS D-PRINT: 74 KTS AT 040600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST

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 30W IS FORECAST TO START TURNING
NORTHEASTWARD OVER THE NEXT 12 HOURS AS IT ROUNDS THE AXIS OF THE
STR TO THE EAST. FOLLOWING TAU 12, THE SPEED OF ADVANCE OF 30W WILL
QUICKLY INCREASE IN RESPONSE TO THE INTERACTION WITH AN INCOMING
MID-LATITUDE TROUGH. 30W WILL THEN ACCELERATE NORTHEASTWARD, ALONG
THE NORTHWESTERN EXTENT OF THE STR THROUGH THE REMAINDER OF THE
FORECAST PERIOD. REGARDING INTENSITY, 30W IS FORECAST TO CONTINUE
STEADILY WEAKENING THROUGH TAU 36 DUE TO INCREASING VERTICAL WIND
SHEAR, DRY AIR ENTRAINMENT, AND DECREASING SEA SURFACE
TEMPERATURES. HOWEVER, THE ROBUST POLEWARD OUTFLOW INTO THE JET
ALONG WITH BAROCLINIC FORCING IS EXPECTED TO ALLOW 30W TO MAINTAIN
TYPHOON-INTENSITY THROUGHOUT ITS TRANSITION INTO A STRONG
EXTRATROPICAL CYCLONE. EXTRATROPICAL TRANSITION IS FORECAST TO
BEGIN AT TAU 36 WITH COMPLETION AROUND TAU 48, ONCE THE SYSTEM
BECOMES EMBEDDED UNDERNEATH THE JET AND SST DROPS BELOW 20 C.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS NOW IN STRONG
AGREEMENT THROUGHOUT THE FORECAST PERIOD WITH THE SOLE EXCEPTION OF
GALWEM, WHICH IS SIGNIFICANTLY FURTHER WEST AND SLOWER THAN THE
REST OF GUIDANCE. DISCOUNTING GALWEM, THE CROSS-TRACK SPREAD AT TAU
48 IS MEASURED TO BE ABOUT 95 NM. THE ALONG-TRACK SPREAD IS ALSO IN
BETTER AGREEMENT WITH THE TAU 48 MEASUREMENT OF 220 NM BETWEEN THE
FAST GOOGLE DEEPMIND AND THE SLOW JGSM. THE JTWC TRACK FORECAST IS
PLACED NEAR THE MODIFIED CONSENSUS (REMOVING GALWEM) WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE AGREES ON GRADUAL WEAKENING THROUGH
TAU 24, BUT THEN SLIGHTLY DIVERGES AFTERWARD. THE GFS AND ECMWF
BOTH SHOW A SLIGHT REINTENSIFICATION PHASE WHILE HAFS-A AND HWRF
SHOW CONTINUOUS WEAKENING. THE JTWC INTENSITY FORECAST CLOSELY
FOLLOWS THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE.

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