WDXS31 PGTW 252100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.3S 106.8E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 510 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 27S (COURTNEY) TRANSITING WEST-SOUTHWESTWARD ALONG THE
NORTHERN PERIPHERY OF A STR TO THE SOUTH. RECENTLY SUBSIDING
NORTHEASTERLY VERTICAL WIND SHEAR (VWS), WHICH IS CURRENTLY
ANALYZED AT 15-20 KTS, ALLOWED THE CONVECTION TO PERSIST AND EXPAND
OVER A PORTION OF THE EASTERN SEMICIRCLE OF THE SYSTEM. ENVIRONMENTAL 
ANALYSIS REVEALS MODERATE POLEWARD AND EQUATORWARD OUTFLOW, WARM (28-
29 C) SEA SURFACE TEMPERATURES (SST) AND DEEP MONSOONAL MOISTURE 
AVAILABLE ALONG THE IMMEDIATE PATH OF TC 27S, MAKING THE CONDITIONS 
MARGINALLY FAVORABLE FOR CONTINUOUS DEVELOPMENT. THE INITIAL POSITION 
IS PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM A 251453Z 
METOP-C ASCAT PASS SHOWING A CLEAR LOW-LEVEL CIRCULATION CENTER 
(LLCC). THE INITIAL INTENSITY OF 45 KTS IS ALSO ASSESSED WITH MEDIUM 
CONFIDENCE BASED ON IMPROVING CONVECTIVE STRUCTURE OF TC COURTNEY, AS 
WELL AS DVORAK FIXES AND OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: 251453Z METOP-C ASCAT SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   APRF: T3.0 - 45 KTS
   CIMSS SATCON: 45 KTS AT 251800Z
   CIMSS ADT: 45 KTS AT 251800Z
   CIMSS AIDT: 37 KTS AT 251800Z
   CIMSS D-MINT: 30 KTS AT 251742Z
   CIMSS D-PRINT: 36 KTS AT 251800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 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 COURTNEY IS FORECAST TO CONTINUE TRACKING
WESTWARD, DUE TO PERSISTENT STEERING PATTERN, CONSISTING OF A STR
TO THE SOUTH, BRIEFLY BROKEN BY A PASSING UPPER-LEVEL TROUGH AROUND 
TAU 36. AFTERWARDS, ANOTHER STR WILL DEVELOP SOUTHWEST OF THE SYSTEM, 
FURTHER NAVIGATING TC 27S ON A GENERALLY WESTWARD TRACK, TRANSITIONING 
INTO A SOUTHWESTWARD MOVEMENT, AS SOON AS THE SYSTEM ROUNDS THE AXIS 
OF THE RIDGE. IN TERMS OF INTENSITY, TC COURTNEY IS CURRENTLY 
BENEFITING FROM A DECREASED VWS AND IS FORECAST TO STEADILY INTENSIFY, 
REACHING THE PEAK OF 65 KTS BY TAU 72. TIMELINE AND RATE OF 
INTENSIFICATION ARE DEPENDENT ON THE LATITUDINAL LOCATION OF THE 
SYSTEM, AS THE STEERING PATTERN TRANSITIONS. ENVIRONMENTAL ANALYSIS
REVEALS COOLER (25-26 C) SST LOCATED APPROXIMATELY SOUTH OF 20S, IN
BETWEEN 85E AND 100E. SIMILARLY, MORE FAVORABLE CONDITIONS IN
REGARD TO VWS REMAIN NORTH OF THE 20S PARALLEL, ALONG THE PATH OF
TC 27S. AFTER TAU 96, AS THE SYSTEM BEGINS TRANSITING POLEWARD,
COOLING SST AND INCREASING DRY AIR ENTRAINMENT WILL LEAD TO STEADY
WEAKENING OF TC 27S.

MODEL DISCUSSION: SHORT TERM (0-72 HR) NUMERICAL MODEL TRACK
GUIDANCE IS IN GOOD AGREEMENT, AS INDICATED BY THE CROSS-TRACK
SPREAD OF 80 NM. ALONG-TRACK HOWEVER, CARRIES MORE UNCERTAINTY WITH
A SPREAD OF 270 NM. ECMWF DETERMINISTIC GUIDANCE IS THE FASTEST,
WHILE NAVGEM OFFERS THE SLOWEST SOLUTION. LONG TERM (72-120 HR)
CROSS-TRACK SPREAD INCREASES TO 160 NM, WHILE ALONG-TRACK SPREAD
REMAINS AT 270 NM, RESULTING IN OVERALL TRACK GUIDANCE TO BE
ASSESSED WITH MEDIUM CONFIDENCE. JTWC TRACK IS PLACED IN CLOSE
PROXIMITY TO THE MULTI-MODEL CONSENSUS SOLUTION. INTENSITY GUIDANCE
IS IN GOOD AGREEMENT ACROSS THE CONSENSUS MEMBERS, WITH ALL MODELS
INDICATING STEADY INTENSIFICATION THROUGH TAU 36. BEYOND THAT
HOWEVER, UNCERTAINTY INCREASES SIGNIFICANTLY, AS WITNESSED BY THREE
POTENTIAL SCENARIOS. HAFS IS INDICATING RAPID INTENSIFICATION,
WITH A PEAK OF 105 KTS AROUND TAU 84. COAMPS-TC IS PORTRAYING A
SLOW, BUT STEADY WEAKENING, DOWN TO 40 KTS BY THE SAME TIME. THE
REMAINDER OF THE AVAILABLE MODELS, AS WELL AS THE MULTI-MODEL
CONSENSUS ARE ALL TIGHTLY GROUPED THROUGHOUT THE FORECAST PERIOD
AND JTWC FORECAST CLOSELY REFLECTS THIS AGREEMENT, SHOWING AN 
INTENSIFICATION WITH A PEAK OF 65-70 KTS BETWEEN TAUS 72 AND 96. 
INCREASING VWS, COMBINED WITH SIGNIFICANT DRY AIR ENTRAINMENT 
OCCURRING AFTER TAU 84 WILL NOT ALLOW TC COURTNEY TO DEVELOP AS 
RAPIDLY AS SUGGESTED BY THE HAFS RUN. GIVEN THE CURRENT OUTPUT 
VARIABILITY AMONG THE MODELS, THE LONG TERM INTENSITY IS ASSESSED WITH 
LOW CONFIDENCE.

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