Advisories

WDPN31 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (IN-FA) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.6N 165.9E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 160 NM NORTHWEST OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
CONVECTION OBSCURING A COMPACT LOW-LEVEL CIRCULATION CENTER (LLCC).
UPPER-LEVEL OUTFLOW REMAINS HEALTHY IN ALL DIRECTIONS, THOUGH THE
CONVECTIVE STRUCTURE HAS NOT APPRECIABLY IMPROVED OVER THE PAST SIX
HOURS. A 241039Z ASCAT-C PASS REVEALED GALE-FORCE WINDS EXTENDING A
SHORT DISTANCE FROM THE CENTER, BUT IT MAY NOT HAVE RESOLVED THE
MAXIMUM WINDS. THE WIND FIELD WAS ALSO SOMEWHAT ASYMMETRIC.
TROPICAL STORM (TS) 30W IS TRAVERSING A GENERALLY FAVORABLE
ENVIRONMENT OF VERY WARM SEA SURFACE TEMPERATURES (SST) OF 29-30
DEGREES CELSIUS AND MODERATE RADIAL OUTFLOW ALOFT; HOWEVER,
MODERATE MID-LEVEL SOUTHEASTERLY SHEAR MAY BE INHIBITING MORE RAPID
DEVELOPMENT. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE SCATTEROMETER DATA. THE INITIAL INTENSITY IS HELD AT
50 KTS WITH MEDIUM CONFIDENCE, BASED ON A BLEND OF THE CIMSS
OBJECTIVE INTENSITY ESTIMATES AND SET SLIGHTLY ABOVE THE SUBJECTIVE
DVORAK FIXES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T2.5 - 35 KTS
   PHFO: T3.0 - 45 KTS
   CIMSS SATCON: 41 KTS AT 240738Z
   CIMSS ADT: 47 KTS AT 241140Z
   CIMSS AIDT: 38 KTS AT 241140Z
   CIMSS D-MINT: 45 KTS AT 241044Z
   CIMSS D-PRINT: 53 KTS AT 241140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 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: TS 30W MAY HAVE BEGUN ITS ANTICIPATED
NORTH-NORTHWESTWARD MOTION. THE CURRENT WEAK STEERING ENVIRONMENT,
PRODUCED BY COMPETING INFLUENCES FROM A NEAR-EQUATORIAL RIDGE (NER)
TO THE SOUTHEAST AND A SUBTROPICAL RIDGE (STR) TO THE NORTHWEST,
WILL TRANSITION OVER THE NEXT 24 HOURS. AS THE NER BUILDS, IT WILL
BECOME THE PRIMARY STEERING INFLUENCE AND DRIVE THE SYSTEM
NORTH-NORTHWESTWARD AT A RELATIVELY SLOW SPEED OF 5-6 KTS. NEAR TAU
48, A DEEP TROUGH PASSING OVER THE KOREAN PENINSULA AND APPROACHING
HONSHU WILL CAUSE THE STR TO REORIENT EASTWARD AND CONSOLIDATE
NORTH OF TS 30W BY TAU 96. AS A RESULT, THE SYSTEM WILL SLOW TO 3-4
KTS FROM TAU 48 TO TAU 72 AND TURN SHARPLY WESTWARD. DURING TAU
96-120, THE NER AND STR WILL MERGE INTO A STRONGER RIDGE.
CONCURRENTLY, A HYBRID SYSTEM WILL FORM EAST OF THE DATE LINE AND
EXPAND EASTWARD, FURTHER ENHANCING THE WESTWARD STEERING FLOW.
THESE FEATURES WILL CAUSE TS 30W TO ACCELERATE WESTWARD DURING THE
LATTER PART OF THE FORECAST PERIOD. ALTHOUGH THE INTENSITY HAS
CHANGED LITTLE OVER THE PAST SIX HOURS AND MODERATE MID-LEVEL SHEAR
PERSISTS, VERY WARM SST AND MODERATE DIVERGENCE ALOFT WILL SUPPORT
FURTHER DEVELOPMENT. THE FORECAST CALLS FOR STEADY INTENSIFICATION
THROUGH TAU 12, ALLOWING TIME FOR THE COMPACT CIRCULATION TO BECOME
MORE AXISYMMETRIC. RAPID INTENSIFICATION (RI) IS FORECAST
THEREAFTER, WITH TS 30W REACHING 90 KTS BY TAU 36. BETWEEN TAU 36
AND TAU 72, THE SLOW TRANSLATION SPEED MAY PROMOTE OCEAN MIXING AND
UPWELLING OF COOLER SUBSURFACE WATERS, LIMITING FURTHER
INTENSIFICATION AND POSSIBLY INDUCING WEAKENING. ONCE THE SYSTEM
GAINS SUFFICIENT FORWARD SPEED AFTER TAU 72, THE GENERALLY
FAVORABLE ENVIRONMENT OF LOW TO MODERATE VERTICAL WIND SHEAR (VWS)
AND VERY WARM SST WILL SUPPORT REINTENSIFICATION.

MODEL DISCUSSION: TRACK GUIDANCE IS GENERALLY SIMILAR TO THE
PREVIOUS CYCLE, WITH JGSM, HAFS-A, GFS, AND THE GEFS ENSEMBLE MEAN
DEPICTING A SHORT-LIVED NORTHEASTWARD TURN NEAR TAU 36, FOLLOWED BY
A SHARP WESTWARD TURN NEAR TAU 72. THIS SCENARIO ASSUMES THE STR
WILL REORIENT EASTWARD MORE SLOWLY THAN FORECAST. ECMWF AND THE
AI-BASED GUIDANCE DEPICT A MORE IMMEDIATE SHARP WESTWARD TURN. THE
JTWC TRACK FORECAST HAS CHANGED LITTLE AND IS PLACED NEAR THE
CENTER OF THE WESTWARD-TRACKING GUIDANCE ENVELOPE. THIS TRACK LIES
SOUTH OF THE ECMWF SOLUTION BUT NEAR THE GOOGLE DEEPMIND GUIDANCE.
INTENSITY GUIDANCE SHOWS A RANGE OF INITIAL INTENSIFICATION RATES
THROUGH TAU 48, FOLLOWED BY SLIGHT WEAKENING OR SLOW
INTENSIFICATION FROM TAU 48 TO TAU 72, AND STEADY INTENSIFICATION
THEREAFTER. THE JTWC INTENSITY FORECAST IS SET NEAR THE LOWER END
OF THE ENVELOPE AND CLOSEST TO DEEPMIND THROUGH TAU 36, NEAR THE
CENTER OF THE SPREAD FROM TAU 48 TO TAU 72, AND NEAR THE UPPER END
FROM TAU 72 TO TAU 120. HAFS-A AND COAMPS-TC STRENGTHEN THE SYSTEM
TO 105-115 KTS BY TAU 48, WHICH IS POSSIBLE IF THE COMPACT
CIRCULATION CAN QUICKLY COMPLETE AXISYMMETRIZATION. DEEPMIND HAS
TRENDED STRONGER THIS CYCLE, WITH 60 PERCENT OF ITS ENSEMBLE
MEMBERS ATTAINING SUPER TYPHOON INTENSITY BY TAU 120.

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