Advisories

WDPN33 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 022//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.2N 150.4E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 495 NM NORTH-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 42 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 27W MAINTAINS AN IMPRESSIVE APPEARANCE IN ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) AND IS LOCATED IN A FAVORABLE
ENVIRONMENT CONSISTING OF LOW VERTICAL WIND SHEAR (VWS), WARM SEA
SURFACE TEMPERATURES NEAR 29 DEGREES CELSIUS, AND MODEST
UPPER-LEVEL DIVERGENCE. A CLEAR, CIRCULAR EYE MEASURING 20-25 NM IN
DIAMETER IS EMBEDDED IN A CENTRAL DENSE OVERCAST (CDO) WITH A
SMOOTH CIRRUS CANOPY. THE UPPER-LEVEL OUTFLOW IS EXPANDING IN ALL
DIRECTIONS, INDICATIVE OF INTENSIFICATION. A 100624Z SSMIS PASS
SHOWCASES A ROBUST EYEWALL WITH A FEW OUTER SPIRAL BANDS. EARLIER
SAR PASSES BY RCM3 AND RSAT2 AT APPROXIMATELY 091940Z INDICATED
PEAK SUSTAINED WINDS NEAR 110 KTS. SINCE THAT TIME, THE EYE HAS
CLEARED, AND THE CLOUD TOP TEMPERATURES ASSOCIATED WITH THE CDO
HAVE REMAINED NEAR -70 DEGREES CELSIUS. BASED ON THE IMPROVED
CONVECTIVE SIGNATURE AND THE T6.0 DVORAK CLASSIFICATION FROM RJTD,
THE INITIAL INTENSITY IS SET AT 115 KTS WITH MEDIUM CONFIDENCE. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
WELL-DEFINED EYE IN THE MSI.

INITIAL WIND RADII BASIS: SCATTEROMETER AND SAR DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED FAR TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T6.0 - 115 KTS
   CIMSS SATCON: 114 KTS AT 100540Z
   CIMSS ADT: 112 KTS AT 100540Z
   CIMSS AIDT: 109 KTS AT 100540Z
   CIMSS D-MINT: 112 KTS AT 100322Z
   CIMSS D-PRINT: 108 KTS AT 100540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 27W WILL CONTINUE ON A NORTHWESTWARD
TRAJECTORY ALONG THE SOUTHWESTERN FLANK OF THE STR AND APPROACH A
WEAKNESS IN THE STR PRODUCED BY TROPICAL STORM (TS) 15E. AS IT
DOES, THE FORWARD SPEED WILL SLOW FROM ITS CURRENT SPEED OF 13 KTS
TO 9-10 KTS NEAR RECURVATURE. THE SYSTEM WILL CROSS THE RIDGE AXIS
AND RECURVE TOWARD THE NORTHEAST AROUND TAU 36. THEREAFTER, THE
VORTEX WILL BECOME INCREASINGLY EMBEDDED IN DEEP-LAYER MID-LATITUDE
WESTERLY FLOW AND ACCELERATE. TY 27W HAS ROUGHLY 12 HOURS REMAINING
OVER OCEAN HEAT CONTENT (OHC) OF 75 KJ PER CM2. THE LOW-SHEAR
ENVIRONMENT AND FAVORABLE OCEAN CONDITIONS WILL ENABLE TY 27W TO
INTENSIFY A LITTLE MORE. AFTER TAU 12, THE SYSTEM WILL TRAVERSE
WATERS WITH AN INCREASINGLY SHALLOW SUBSURFACE WARM WATER LAYER.
COUPLED WITH THE 9-11 KTS OF TRANSLATION SPEED PREDICTED OVER THE
NEXT 36 HOURS, THE DECLINING OHC WILL LEAD TO A WEAKENING TREND
COMMENCING NEAR TAU 24. THE WEAKENING TREND WILL ACCELERATE AFTER
TAU 24 AS THE VORTEX ENCOUNTERS PROGRESSIVELY COOLER WATERS,
CROSSING THE 26 DEGREES CELSIUS ISOTHERM BY TAU 72. THE SYSTEM WILL
BEGIN EXTRATROPICAL TRANSITION (ETT) BY TAU 96 AND COMPLETE ETT BY
TAU 120.

MODEL DISCUSSION: TRACK GUIDANCE IS IN EXCELLENT AGREEMENT THROUGH
TAU 72, WITH A CROSS-TRACK SPREAD INCREASING FROM 50 NM AT TAU 36
TO 110 NM AT TAU 72. FROM TAU 72 TO TAU 120, GFS AND HAFS-A ARE THE
POLEWARD OUTLIERS AND NAVGEM IS THE EQUATORWARD OUTLIER AND ALSO
THE FASTEST. THE JTWC FORECAST TRACK IS POSITIONED ALONG THE CORE
GROUPING OF MODELS THROUGH TAU 72 AND IS THEN ALIGNED WITH A BLEND
OF THE MULTI-MODEL CONSENSUS (CONW) AND THE AI-MODEL MEAN. THE
FORECAST TRACK IS CLOSEST TO GOOGLE DEEPMIND AND ECMWF. GIVEN
RECENT SATELLITE TRENDS, THE JTWC INTENSITY FORECAST FOR THE FIRST
36 HOURS IS SET NEAR THE UPPER END OF THE GUIDANCE ENVELOPE,
SLIGHTLY ABOVE DEEPMIND AND HAFS-A, WHICH KEEP THE INTENSITY AT 115
KTS THROUGH TAU 12. THE INTENSITY FORECAST THEN FOLLOWS THE
CONSENSUS THROUGH TAU 48 AND APPROACHES THE WEAKER GFS AND DEEPMIND
SOLUTIONS TOWARD THE END OF THE FORECAST PERIOD.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: HIGH
   INTENSITY 72-120 HR: MEDIUM//
NNNN