Advisories

WDPN31 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 049//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.8N 138.4E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 168 NM WEST-NORTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
30W (IN-FA) WITH A CENTRAL DENSE OVERCAST (CDO) THAT IS SHEARED TO
THE EAST OF AN EXCEPTIONALLY WELL-DEFINED LOW-LEVEL CIRCULATION
CENTER (LLCC). A 040846Z SENTINEL-1C SAR IMAGE MEASURED A VMAX OF
87 KTS LOCATED WITHIN THE NORTHEASTERN QUADRANT WITH A RADIUS OF
MAXIMUM WINDS OF 19 NM. A 041153Z METOP-C MHS IMAGE REVEALED
EXPOSED LOW-LEVEL CLOUD LINES TIGHTLY WRAPPING INTO THE DEFINED
CENTER, LENDING HIGH CONFIDENCE TO THE INITIAL POSITION PLACEMENT.
THE INITIAL INTENSITY OF 80 KTS AND WIND RADII ARE BOTH ASSESSED
WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED SAR IMAGE. THE
PGTW AND RJTD DVORAK FIXES OF T4.5 FURTHER SUPPORT THE INITIAL
INTENSITY ASSESSMENT. ENVIRONMENTAL ANALYSIS INDICATES THAT 30W IS
IN A MARGINAL ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW
ALOFT, HIGH (25-30 KTS) VERTICAL WIND SHEAR, BORDERLINE SEA SURFACE
TEMPERATURES (26-27 C), AND DRY AIR ENTRAINMENT.

INITIAL WIND RADII BASIS: PERSISTENCE FROM A 040846Z SENTINEL-1C
SAR PASS

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: 72 KTS AT 041200Z
   CIMSS AIDT: 82 KTS AT 041200Z
   CIMSS D-MINT: 77 KTS AT 041134Z
   CIMSS D-PRINT: 69 KTS AT 041200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST

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 30W APPEARS TO BE AT THE VERY BEGINNING OF
THE EXPECTED NORTHEASTWARD TURN. 30W IS FORECAST TO BEGIN
INTERACTING WITH AN INCOMING MID-LATITUDE TROUGH WITHIN THE NEXT
6-12 HOURS AND INCREASE TRACK SPEED. THE SYSTEM WILL THEN
ACCELERATE IN THE NORTHEASTWARD DIRECTION AS IT TRAVERSES THE
NORTHWESTERN EXTENT OF THE STR AND INITIATES EXTRATROPICAL
TRANSITION (ETT). 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 MAX
ALONG WITH BAROCLINIC FORCING IS EXPECTED TO ALLOW 30W TO MAINTAIN
TYPHOON-INTENSITY THROUGHOUT ITS TRANSITION INTO A STRONG
EXTRATROPICAL CYCLONE. ETT IS FORECAST TO START AT TAU 24 AND
COMPLETE AROUND TAU 36, ONCE THE SYSTEM BECOMES EMBEDDED UNDERNEATH
THE JET AND SST DROPS BELOW 20 C.

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT WITH THE
SOLE EXCEPTION OF GALWEM, WHICH IS A SLOW AND WESTWARD OUTLIER.
DISCOUNTING GALWEM, THE CROSS-TRACK SPREAD AT TAU 36 IS MEASURED TO
BE JUST 60 NM. THE ALONG-TRACK SPREAD IS RELATIVELY LARGER AND IS
MEASURED TO BE 180 NM BETWEEN THE FAST GOOGLE DEEPMIND AND THE SLOW
JGSM AT TAU 36. THE JTWC TRACK FORECAST IS PLACED NEAR THE MODIFIED
CONSENSUS (REMOVING GALWEM) WITH HIGH CONFIDENCE. INTENSITY
GUIDANCE CONTINUES TO BE SLIGHTLY SPLIT WITH GFS AND ECMWF BOTH
SHOWING A REINTENSIFICATION PHASE AS THE SYSTEM COMPLETES ETT. ON
THE OTHER HAND, THE VARIOUS MESOSCALE MODELS AND GOOGLE DEEPMIND
ALL DEPICT GRADUAL WEAKENING. THE JTWC INTENSITY FORECAST REMAINS 
CLOSELY IN LINE WITH THE MULTI-MODEL CONSENSUS WITH MEDIUM 
CONFIDENCE.

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