Advisories

WDPN31 PGTW 272100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.7N 160.8E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 870 NM EAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 30W WITH A BROAD AND RAGGED EYE THAT HAS BEGUN TO CLEAR OUT
OVER THE PAST FEW HOURS. ALTHOUGH THE INTERIOR OF THE EYE IS
RAGGED, THE SURROUNDING DEEP CONVECTION HAS ESTABLISHED ITSELF AS A
SYMMETRIC EYEWALL AS WHAT LITTLE REMAINS OF THE PREVIOUS SMALLER
DIAMETER EYE CLEARS OUT. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE CENTER OF THE EYE IN EIR. THE INITIAL
INTENSITY OF 115 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON
UNANIMOUS T6.0 AGENCY DVORAK FIXES AND SUPPORTED BY THE CIMSS
OBJECTIVE INTENSITY ESTIMATES. THE ENVIRONMENT IS CHARACTERIZED AS
FAVORABLE, WITH WARM SEA SURFACE TEMPERATURES, GOOD RADIAL OUTFLOW
ALOFT, AND LOW VERTICAL WIND SHEAR. THE SYSTEM HAS ALSO STARTED TO
TRANSIT WEST-NORTHWESTWARD AT A SPEED OF 7 KTS, REDUCING THE EFFECT
ANY PREVIOUS COLD WATER UPWELLING MIGHT HAVE HAD.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN FLANK OF A SUBTROPICAL RIDGE
EXTENSION CENTERED TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.0 - 115 KTS
   PHFO: T6.0 - 115 KTS
   CIMSS SATCON: 115 KTS AT 271600Z
   CIMSS ADT: 127 KTS AT 271800Z
   CIMSS AIDT: 112 KTS AT 271800Z
   CIMSS D-MINT: 112 KTS AT 271532Z
   CIMSS D-PRINT: 114 KTS AT 271800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 GRADUALLY ACCELERATE
WEST-NORTHWESTWARD OVER THE NEXT 24 HOURS AS A NEAR-EQUATORIAL
RIDGE TO THE SOUTH WEAKENS AND MIGRATES WESTWARD, RELINQUISHING
STEERING CONTROL TO THE STR EXTENSION BUILDING TO THE NORTH OF THE
SYSTEM. THE TRACK CONTINUES WEST-NORTHWESTWARD THROUGH TAU 72 IN
THIS ENVIRONMENT. A SECONDARY STR WILL BUILD IN FROM THE WEST,
CREATING A COL REGION AND WEAK STEERING ENVRIONMENT FROM TAU 72
ONWARDS. THE SYSTEM IS EXPECTED TO HAVE A PERIOD OF ERRATIC AND
SOMETIMES QUASI-STATIONARY MOTION DURING THAT TIME, ALTHOUGH THAT
CANNOT BE EXPLICITLY REPRESENTED IN THE TRACK FORECAST. THE TRACK
FORECAST INSTEAD PLACES THE POSITION AT TAU 96 AND 120 IN THE
GENERAL AREA OF THE MEAN MOTION VECTOR. THE INTENSITY FORECAST THE
RECENT STRUCTURAL IMPROVEMENT OF TY 30W WITH STEADY INTENSIFICATION
TO 125 KTS OVER THE NEXT 24 HOURS. THE INTENSITY FORECAST IS CAPPED
THERE BECAUSE OF THE LACK OF A WELL DEFINED OUTFLOW MECHANISM AND
THE POTENTIAL FOR ADDITIONAL ATTEMPTS AT EYEWALL REPLACEMENT
CYCLES. A STEADY WEAKENING AFTER TAU 48 IS DEPICTED BY THE HAFS-A
MODEL AS A RESULT OF SLIGHTLY COOLER SEA SURFACE TEMPERATURES AND
LOWER OHC CONTRIBUTING TO MORE COLD WATER UPWELLING, ESPECIALLY IN
THE LATER TAUS WHEN THE TRACK MOTION SLOWS AGAIN.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN VERY GOOD AGREEMENT
THROUGH TAU 72, WITH A CROSS-TRACK SPREAD OF 60 NM AT THAT TIME AND
MINIMAL ALONG-TRACK SPREAD. AFTER TAU 72 THE GUIDANCE SUITE DEPICTS
A VARIETY OF SOLUTIONS WITH A FAIRLY WIDE SPREAD, BUT GENERALLY
WITH WESTWARD AND SOUTHWARD COMPONENTS. THE JTWC TRACK FORECAST IS
PLACED NEAR THE CONSENSUS THROUGH TAU 72, THEN IN A SUBJECTIVE MEAN
AMONG THE SPREAD OF GUIDANCE THROUGH TAU 120. THE INTENSITY
GUIDANCE HAS SETTLED INTO TWO GROUPS, WITH HAFS-A AND GOOGLE
DEEPMIND MODELS ON THE HIGH END OF THE ENVELOPE WHILE THE REST OF
THE GUIDANCE STAYS FLAT WITH A SLOW WEAKENING TREND IN THE LATER
TAUS. THE JTWC INTENSITY FORECAST IS PLACED ON THE LOWER END OF THE
MORE INTENSE GROUPING.

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