Advisories

WDPN31 PGTW 261500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.1N 162.7E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 384 NM SOUTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SLOWLY
DETERIORATING CONVECTIVE STRUCTURE, WITH WARMING CLOUD TOP
TEMPERATURES ASSOCIATED WITH THE CENTRAL DENSE OVERCAST AND COOLING
EYE TEMPERATURES. TY 30W HAS BEEN MOVING AT 3-4 KTS OVER THE PAST
12 HOURS AS IT TURNS WESTWARD. THE SLOW SPEED HAS LIKELY INDUCED
UPWELLING OF COOL SUBSURFACE WATERS, WHICH WOULD EXPLAIN THE
DETERIORATING CLOUD PATTERN. ADDITIONALLY, AN UPPER-LEVEL TROUGH TO
THE NORTH HAS INDUCED MODERATE TO HIGH WEST-NORTHWESTERLY VERTICAL
WIND SHEAR (VWS), RESTRICTING UPPER-LEVEL POLEWARD OUTFLOW. THESE
DETRIMENTAL FACTORS HAVE CAUSED THE UPWARD INTENSITY TREND TO LEVEL
OFF. A 260727Z RCM-2 SAR PASS ESTIMATED MAXIMUM WINDS NEAR 115 KTS.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
SMALL EYE IN EIR IMAGERY. DESPITE THE DEGRADED SATELLITE
PRESENTATION, THE INITIAL INTENSITY HAS BEEN HELD AT 115 KTS TO
REFLECT A TIME LAG BETWEEN THE WEAKER SATELLITE APPEARANCE AND
LOWER WINDS. THIS ASSESSMENT IS SUPPORTED BY THE T6.0 DVORAK
CLASSIFICATIONS FROM PGTW AND PHFO AS WELL AS THE EARLIER SAR DATA.
THE CIRCULATION REMAINS VERY COMPACT, AS A 260937Z ASCAT-B PASS
REVEALED A SYMMETRIC WIND FIELD, WITH GALES EXTENDING NO MORE THAN
70 NM FROM THE CENTER.

INITIAL WIND RADII BASIS: SCATTEROMETER AND SAR DATA 

CURRENT STEERING MECHANISM: SOUTHEASTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) CENTERED SOUTH OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.5 - 102 KTS
   PHFO: T6.0 - 115 KTS
   CIMSS SATCON: 108 KTS AT 260730Z
   CIMSS ADT: 117 KTS AT 261130Z
   CIMSS AIDT: 106 KTS AT 261130Z
   CIMSS D-MINT: 116 KTS AT 260936Z
   CIMSS D-PRINT: 109 KTS AT 261130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK EASTWARD
   OTHER FACTORS: UPWELLING OF COOL SUBSURFACE WATERS

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 IS EXECUTING THE EXPECTED WESTWARD TURN
AS THE DEEP-LAYER STR TO THE NORTHWEST SHIFTS EASTWARD. THE SYSTEM
WILL THEN ACCELERATE ALONG A WESTWARD TO WEST-NORTHWESTWARD
TRAJECTORY. TOWARD TAU 96, THE VORTEX WILL BEGIN TO ROUND THE
SOUTHWESTERN PERIPHERY OF THE RIDGE AND TURN NORTHWESTWARD TOWARD A
LARGE WEAKNESS CAUSED BY A BROAD MID-LEVEL TROUGH OVER HONSHU.
CONCURRENTLY, A SEPARATE STR POSITIONED OVER SOUTHEAST CHINA WILL
BUILD EASTWARD. THE NET EFFECT WILL BE A SLOWER RATE OF MOTION
TOWARD THE END OF THE FORECAST PERIOD. THE PRESENT MOTION OF 3-4
KTS HAS LIKELY INDUCED UPWELLING OF COOLER SUBSURFACE WATERS. THIS
IS EXPLICITLY DEPICTED BY THE HAFS-A MESOSCALE MODEL ANALYSIS,
WHICH IS COUPLED TO THE OCEAN. THE COOLER SST AND ONGOING VWS WILL
CAUSE SOME NEAR-TERM WEAKENING. HOWEVER, VWS WILL QUICKLY SUBSIDE
OVER THE NEXT 12-24 HOURS AS THE TROUGH RACES DOWNSTREAM, WHILE OHC
REMAINS HIGH AT AROUND 100-110 KJ PER CM2 ALONG THE FORECAST TRACK.
AS THE SYSTEM GAINS A HIGHER TRANSLATION SPEED, THESE FAVORABLE
CONDITIONS WILL SUPPORT REINTENSIFICATION THROUGH TAU 96, AFTER
WHICH A PATCH OF LOWER OHC WILL RESULT IN SOME WEAKENING. THE PEAK
INTENSITY OF TY 30W WILL LARGELY BE GOVERNED BY INTERNAL TROPICAL
CYCLONE STRUCTURAL PROCESSES THAT ARE DIFFICULT TO PREDICT.

MODEL DISCUSSION: TRACK GUIDANCE IS IN EXCELLENT AGREEMENT THROUGH
TAU 96, THOUGH THE SPREAD INCREASES SUBSTANTIALLY AT TAU 120 DUE TO
UNCERTAINTIES IN THE EVOLUTION OF THE RIDGE OVER SOUTHEAST CHINA
AND THE BROAD TROUGH OVER HONSHU. THE JTWC FORECAST TRACK IS
POSITIONED ALONG THE SOUTHERN SIDE OF THE CORE GUIDANCE ENVELOPE
THROUGH TAU 96, NEAREST TO THE AI-MODEL MEAN, WHICH HAS PERFORMED
WELL. AIFS AND DEEPMIND ARE THE SOUTHERNMOST SOLUTIONS, PASSING
WITHIN 100-140 NM OF TINIAN. CONFIDENCE DECREASES TO MEDIUM BY TAU
120 AS THE GUIDANCE ENVELOPE EXPANDS. INTENSITY GUIDANCE HAS A
MODERATE SPREAD. COAMPS-TC AND DEEPMIND DEPICT EITHER STEADY
INTENSITY OR NEAR-TERM WEAKENING FOLLOWED BY A SECOND ROUND OF
INTENSIFICATION. HAFS-A DEPICTS A PEAK INTENSITY OF 160 KTS, WHILE
DEEPMIND AND COAMPS-TC ARE MORE MODEST AT 130-135 KTS. THE JTWC
INTENSITY FORECAST FOR THE FIRST HALF OF THE FORECAST PERIOD
REFLECTS THE EXPECTED SHORT-TERM WEAKENING. HOWEVER,
REINTENSIFICATION TO SUPER TYPHOON STRENGTH IS BECOMING MORE
LIKELY, WITH APPROXIMATELY 80 PERCENT OF MEMBERS IN THE DEEPMIND
AND COAMPS-TC ENSEMBLES ATTAINING THAT THRESHOLD.

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