Advisories

WDPN33 PGTW 052100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (KOGUMA) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.2N 167.6E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 210 NM NORTH OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TS 27W HAS TURNED TOWARD THE NORTH-NORTHWEST AND BECOME MORE
ORGANIZED OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY DEPICTS PERSISTENT, FLARING CONVECTION OVER THE
NORTHWESTERN PORTION OF A STEADILY DEVELOPING LOW-LEVEL CIRCULATION
EVIDENT IN A 051647Z SSMIS PASS. THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON A NASCENT CENTER FEATURE EVIDENT IN
37 GHZ IMAGERY FROM THE 051647Z SSMIS PASS AND RECENT POSITION
FIXES FROM PGTW AND RCTP. THE INITIAL INTENSITY OF 40 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A CONSENSUS OF THE
MULTI-AGENCY SUBJECTIVE DVORAK AND AUTOMATED INTENSITY ESTIMATES
LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: NEAR EQUATORIAL RIDGING (NER) TO THE
EAST, TRANSITIONING TO EXTENSION OF SUBTROPICAL RIDGING (STR) TO
THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.5 - 35 KTS
   CIMSS SATCON: 36 KTS AT 051500Z
   CIMSS ADT: 47 KTS AT 051740Z
   CIMSS AIDT: 38 KTS AT 051740Z
   CIMSS D-MINT: 38 KTS AT 051502Z
   CIMSS D-PRINT: 38 KTS AT 051740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 27W WILL CONTINUE ITS TURN TOWARD A
GENERALLY WEST-NORTHWESTWARD TRAJECTORY OVER THE NEXT 24 HOURS AS
AN EXTENSION OF SUBTROPICAL RIDGING TO THE NORTHEAST BUILDS ON THE
POLEWARD SIDE OF THE SYSTEM. AFTER TAU 96, THE STORM TRACK BEGIN A
POLEWARD TURN AROUND THE SOUTHWESTERN EDGE OF THE STEERING RIDGE. 
AHEAD OF A DEVELOPING MIDLATITUDE SHORTWAVE TROUGH TO THE NORTHWEST. 
THE CURRENT FORECAST ANTICIPATES SLOW BUT STEADY INTENSIFICATION IN 
THE NEAR-TERM, SUPPORTED BY MODERATE POLEWARD OUTFLOW AND CONSTRAINED 
BY LOW TO MODERATE EASTERLY VERTICAL WIND SHEAR, WHICH IS EXPECTED TO
PEAK AROUND TAU 36. THEREAFTER, DECREASING VERTICAL WIND SHEAR AND
IMPROVING OUTFLOW - FIRST EQUATORWARD AND LATER POLEWARD - WILL
SUPPORT A HIGHER RATE OF INTENSIFICATION THROUGH TAU 96.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT REGARDING THE OVERALL FORECAST SCENARIO, ALBEIT WITH
SIGNIFICANT SPREAD PARTICULARLY IN THE CROSS-TRACK DIRECTION DUE TO
DIFFERING DEPICTIONS OF THE EXTENT AND ORIENTATION OF THE BUILDING
SUBTROPICAL STEERING RIDGE TO THE NORTHEAST OF THE SYSTEM. THE
CURRENT TRACK FORECAST IS CONSISTENT WITH THE PREVIOUS JTWC
FORECAST, THE AI MODEL CONSENSUS, AND TOP PERFORMING PHYSICAL
MODELS INCLUDING THE ECMWF DETERMINISTIC MODEL AND ENSEMBLE MEAN
AND MOGREPS ENSEMBLE MEAN FORECASTS, WITH MEDIUM CONFIDENCE.
INTENSITY FORECAST GUIDANCE, INCLUDING HAFS-A, DEPICTS A HIGHER
RATE OF INTENSIFICATION SOONER THAN THE PREVIOUS RUN, WHICH IS
SUPPORTABLE GIVEN CURRENT TRENDS IN STORM STRUCTURE AND A GENERALLY
FAVORABLE ENVIRONMENT ASIDE FROM PERSISTENT LOW TO MODERATE
EASTERLY VERTICAL WIND SHEAR. THERE IS LOW CONFIDENCE IN FORECAST
INTENSITIES FOR THE EXTENDED PERIOD AS THE SYSTEM COULD EASILY
EXCEED THE 110 KNOT PEAK IN THE CURRENT FORECAST GIVEN ITS SMALL
SIZE AND ANTICIPATED, CORRESPONDING SENSITIVITY TO SUPPORTIVE
CONDITIONS IN THE SURROUNDING ENVIRONMENT.  

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