WDXS31 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING 
NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.4S 102.2E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 438 NM SOUTHEAST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 27S (COURTNEY) WITH PERSISTENT DEEP CONVECTION
POSITIONED OVER AN OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC).
ALONG THE WESTERN FLANK, COLD-AIR STRATOCUMULUS FIELDS HAVE BEEN
OBSERVED WRAPPING INTO THE NORTHERN SEMICIRCLE. ALOFT, MODERATE
EQUATORWARD OUTFLOW HAS BEEN OBSERVED ON ANIMATED WATER VAPOR
IMAGERY, WITH VISIBLE CIRRIFORM FILAMENTS EXTENDING NORTHWARD, AND
A SECONDARY WEAK POLEWARD CHANNEL AS THE CYCLONE TRACKS ALONG THE
NORTHEASTERN EXTENT OF THE STR. RECENTLY, DEEP CONVECTION ON
ANIMATED SATELLITE IMAGERY HAS STARTED TO INDICATE FURTHER
INTENSIFICATION WITH UPPER-LEVEL RADIAL OUTFLOW BURSTING OUTWARD
FROM THE SYSTEMS VERTICAL STRUCTURE. ENVIRONMENTAL ANALYSIS SHOWS
THAT TC 27S REMAINS IN A FAVORABLE ENVIRONMENT, WITH LOW (10-15
KTS) VERTICAL WIND SHEAR (VWS), WARM (27-28 C) SEA SURFACE
TEMPERATURES (SST), AND A RELATIVELY MOIST CORE. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON ANIMATED EIR
SATELLITE IMAGERY AND EXTRAPOLATION FROM EARLIER 261433Z METOP-C
ASCAT WIND DATA. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON AGENCY DVORAK FIX ESTIMATES, CIMSS OBJECTIVE
INTENSITY ESTIMATES, AND THE AFOREMENTIONED METOP-C ASCAT WIND
DATA.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   DEMS: T4.0 - 65 KTS
   APRF: T4.5 - 77 KTS
   CIMSS SATCON: 59 KTS AT 261330Z
   CIMSS ADT: 59 KTS AT 261900Z
   CIMSS AIDT: 53 KTS AT 261900Z
   CIMSS D-MINT: 56 KTS AT 261204Z
   CIMSS D-PRINT: 59 KTS AT 261900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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: TC 27S IS FORECASTED TO TRACK WESTWARD ALONG
THE NORTHWESTERN EXTENT OF A DEEP-LAYER STR POSITIONED TO THE
SOUTHEAST THROUGH TAU 48. AFTER TAU 48, THE SYSTEM WILL BEGIN ITS
SOUTHWESTWARD TRACK AROUND THE WESTERN PERIPHERY OF THE SAME
STEERING RIDGE. THE CYCLONE WILL CONTINUE ON A GENERALLY
SOUTHWESTWARD TRACK BETWEEN TAU 48 AND TAU 120, NEARING THE
SUBTROPICAL RIDGE AXIS AT THE END OF THE FORECAST PERIOD. WITH
REGARD TO INTENSITY, TC COURTNEY IS FORECASTED TO STEADILY
INTENSIFY UNTIL TAU 48 TO 90 KTS AS THE ENVIRONMENT REMAINS
FAVORABLE WITH WARM SST, LOW VWS, AND UPPER-LEVEL OUTFLOW SUPPORT.
AFTER TAU 48, THE CYCLONE WILL BEGIN ENCOUNTERING ENHANCED VWS OF
OVER 20 KTS AT THE SAME TIME THE SYSTEM NEARS THE 26C ISOTHERM
DIRECTLY TO THE SOUTH. WHILE THE SYSTEM ROUNDS THE WESTERN
PERIPHERY OF THE STR, THE MARGINAL ENVIRONMENT WILL BEGIN THE
INITIAL WEAKENING PHASE TO 80 KTS BY TAU 72, AND EVENTUALLY TO 55
KTS AT TAU 120 AS VWS ASSOCIATED THE EXPECTED MID-LATITUDE
INTERACTION INCREASES TO OVER 40 KTS AND CREATES A LARGELY
NON-CONDUCIVE ENVIRONMENT FOR FURTHER TC SUPPORT. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
WITH REGARD TO THE TRACK OF TC 27S DURING THE INITIAL 72 HOURS OF THE 
FORECAST PERIOD. THE CROSS-TRACK SPREAD REMAINS STEADY NEAR 60 NM 
UNTIL TAU 48, WITH ALL JTWC CONSENSUS MEMBERS ILLUSTRATING A WESTWARD 
TRACK. AFTER TAU 48, THE CROSS-TRACK DISTANCE SPREADS CONSIDERABLY, 
EXTENDING TO 715 NM BY TAU 120. DUE TO THE UNCERTAINTY AFTER TAU 48, 
THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE DURING THE 
INITIAL 72 HOURS OF THE FORECAST PERIOD, AND LOW THEREAFTER. 
UNFORTUNATELY, INTENSITY GUIDANCE HAS CONTINUED TO ILLUSTRATE 
UNCERTAINTY THROUGHOUT THE ENTIRETY OF THE FORECAST PERIOD. GFS, 
COAMPS-TC, AND HWRF REMAIN ON THE LOWER END OF INTENSITY ESTIMATES, 
PEAKING AT 90 KTS NEAT TAU 72. ON THE UPPER END, HAFS-A REACHES A 
MAXIMUM OF AROUND 120 KTS BETWEEN TAU 60 AND TAU 72. WITH THAT BEING 
SAID, ECMWF ENSEMBLE SOLUTIONS CHARACTERIZE INTENSITIES BETWEEN 80-
100 KTS, WHILE GFS ENSEMBLE SOLUTIONS CONTINUE TO SHOW SUSTAINED 
SURFACE INTENSITIES BETWEEN 40-60 KTS. THE JTWC INTENSITY FORECAST IS 
PLACED WITH LOW CONFIDENCE THROUGH TAU 120 AND PLACED SLIGHTLY ABOVE 
THE JTWC INTENSITY CONSENSUS AS THE ENVIRONMENT IS EXPECTED TO REMAIN 
FAVORABLE UNTIL TAU 72, THEN BECOME NON-CONDUCIVE FOR FURTHER TC 
SUPPORT BETWEEN TAU 72 AND TAU 120.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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