Advisories

WDPN31 PGTW 290900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.3N 152.9E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 415 NM EAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 55 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TY 30W WITH
A SEMI-ANNULAR CONVECTIVE STRUCTURE AND A CLOUD-FREE, 40-NM-WIDE
EYE THAT HAS GRADUALLY WARMED TO +16 DEGREES CELSIUS. OVER THE PAST
SIX HOURS, DEEP CONVECTION HAS CONTINUED TO CYCLE IN THE UPSHEAR
SEMICIRCLE UNDER LOW TO MODERATE VERTICAL WIND SHEAR (VWS), AND
CLOUD-TOP TEMPERATURES HAVE COOLED. THE CENTRAL DENSE OVERCAST
(CDO), WHICH PREVIOUSLY SHOWED A WEAKNESS IN THE NORTHERN
SEMICIRCLE, HAS BECOME MORE SYMMETRIC. A 282308Z ASCAT-B UHR IMAGE
REVEALED THAT THE WIND FIELD HAS EXPANDED, AND THE CORE OF STORM-
AND TYPHOON-FORCE WINDS IS RATHER LARGE. THE UHR SCATTEROMETER DATA
ALSO ESTIMATED PEAK WINDS OF 115 KTS AT THAT TIME. BECAUSE THE
STORM'S SATELLITE APPEARANCE HAS IMPROVED SINCE THEN, THE INITIAL
INTENSITY HAS BEEN RAISED TO 120 KTS WITH MEDIUM CONFIDENCE. THIS
ASSESSMENT LIES NEAR THE HIGHER END OF THE AVAILABLE SUBJECTIVE AND
OBJECTIVE ESTIMATES. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE WELL-DEFINED EYE IN MSI. THE ENVIRONMENT IS
LARGELY FAVORABLE, WITH SUFFICIENTLY HIGH OCEAN HEAT CONTENT (OHC),
LOW VERTICAL WIND SHEAR (VWS), AND MODERATE RADIAL OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR 26N 165E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T5.0 - 90 KTS
   CIMSS SATCON: 120 KTS AT 290510Z
   CIMSS ADT: 102 KTS AT 290600Z
   CIMSS AIDT: 115 KTS AT 290600Z
   CIMSS D-MINT: 115 KTS AT 290645Z
   CIMSS D-PRINT: 119 KTS AT 290600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 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 30W HAS ACCELERATED WEST-NORTHWESTWARD TO
17 KTS ALONG THE SOUTHWESTERN PERIPHERY OF THE STR, A MOTION THAT
WILL CONTINUE OVER THE NEXT 24 HOURS. THEN, A LONGWAVE TROUGH
PASSING OVER HONSHU WILL CREATE A LARGE WEAKNESS IN THE STR,
ALLOWING TY 30W TO TURN POLEWARD AND SLOW DOWN. THE PROGRESSIVE
TROUGH WILL PASS QUICKLY, AND A SEPARATE STR TO THE WEST WILL BUILD
EASTWARD AND CLOSE OFF THE OPENING. THIS EVOLUTION SHOULD CAUSE TY
30W TO DEFLECT WESTWARD. AT THE END OF THE FORECAST PERIOD, ANOTHER
TROUGH PASSING TO THE NORTH MAY CREATE ANOTHER OPENING. THE
FORECAST ACCORDINGLY SLOWS THE SYSTEM AT TAU 120 AND DEPICTS THE
BEGINNING OF A SECOND POLEWARD TURN. THE INTENSITY OF TY 30W WILL
LARGELY BE GOVERNED BY INTERNAL CHANGES IN ITS STRUCTURE AND SMALL
CHANGES IN THE ENVIRONMENT OVER THE NEXT 48 HOURS. CONDITIONS WILL
REMAIN FAVORABLE, WITH LOW VWS AND SUFFICIENTLY HIGH OHC VALUES.
THE CURRENT INTENSIFICATION OF TY 30W IS CONSISTENT WITH A SLIGHT
DECREASE IN SHEAR AND A SLIGHT INCREASE IN OHC. THEREFORE, THE
FORECAST CALLS FOR CONTINUED MODEST INTENSIFICATION TO 125 KTS AT
TAU 12 AS THE SYSTEM MOVES OVER A SMALL POCKET OF SLIGHTLY HIGHER
OHC. THE AVERAGE OHC APPEARS TO BE SLIGHTLY LOWER AFTER TAU 12, SO
THE FORECAST HOLDS THE INTENSITY STEADY AT 120 KTS FROM TAU 24 TO
TAU 48. THEREAFTER, A SIGNIFICANT SLOWING OF THE TRANSLATION SPEED
WILL LIKELY PROMOTE UPWELLING OF COOLER WATERS, RESULTING IN A
PERIOD OF STEADY WEAKENING. THE AMOUNT OF WEAKENING WILL DEPEND ON
THE TIME REQUIRED TO MAKE THE TURN AND THE LATITUDE OF THE TURN, AS
THE STORM CENTER WILL STRADDLE A SHARP GRADIENT IN OHC VALUES. THE
INTENSITY BEYOND TAU 60 WILL DEPEND ON THE STRUCTURE AND SIZE OF
THE SYSTEM, AND IT REMAINS TO BE DETERMINED WHETHER TY 30W CAN
RECOVER BEFORE IT SLOWS DOWN FOR A SECOND TIME AND BEGINS A FINAL
POLEWARD TURN AT TAU 120.

MODEL DISCUSSION: TRACK GUIDANCE IS IN EXCELLENT AGREEMENT THROUGH
TAU 48. BY TAU 60, THE SOLUTIONS DIVERGE. MOST PHYSICS-BASED
MODELS, EXCLUDING NAVGEM, ECMWF, AND JGSM, DEPICT A SOFTER WESTWARD
TURN. THE AI GUIDANCE SHOWS A SLIGHT NORTH-NORTHEASTWARD MOTION
FOLLOWED BY A SHARP U-TURN TOWARD THE WEST. THIS DIVERGENCE RESULTS
IN A LARGE CROSS-TRACK AND ALONG-TRACK SPREAD BEYOND TAU 48. THE
JTWC FORECAST TRACK IS SIMILAR TO THE PREVIOUS FORECAST AND IS
POSITIONED NEAR THE MULTI-MODEL CONSENSUS (CONW), AT THE CENTER OF
THE TIGHT GUIDANCE ENVELOPE THROUGH TAU 48. FROM TAU 60 TO TAU 120,
THE JTWC FORECAST HEDGES TOWARD THE AI-MODEL MEAN. THE JTWC
INTENSITY FORECAST IS SET AT THE HIGH END OF THE GUIDANCE ENVELOPE
THROUGH TAU 48 TO REFLECT CURRENT SATELLITE TRENDS AND THE
PREDICTED ENVIRONMENTAL CONDITIONS, THEN LEANS TOWARD THE INTENSITY
CONSENSUS (ICNW). THE SPREAD AMONG THE GUIDANCE IS QUITE LARGE
DURING THE LATTER PORTION OF THE FORECAST PERIOD, WITH HAFS-A
DEPICTING REINTENSIFICATION TO 125 KTS AND GOOGLE DEEPMIND
DEPICTING WEAKENING TO 90 KTS.

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