WDXS31 PGTW 260900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING 
NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.0S 104.1E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 543 NM SOUTHEAST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 27S (COURTNEY) WITH PERSISTENT DEEP CONVECTION OBSCURING
THE LOW-LEVEL CIRCULATION CENTER (LLCC). OUTFLOW HAS NOTABLY
INCREASED OVER THE PAST 6 HOURS, WITH STRONG RADIAL OUTFLOW NOW
PRESENT. A 260503Z GPM GMI 89 GHZ MICROWAVE IMAGE REVEALED THE
CONVECTIVE BANDING TIGHTLY WRAPPING INTO THE CENTER. THE
CORRESPONDING 37 GHZ MICROWAVE IMAGES DO SHOW THAT A WELL-DEFINED
MICROWAVE EYE HAS YET TO FORM THOUGH. ENVIRONMENTAL ANALYSIS
INDICATES THAT 27S IS IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY
STRONG RADIAL OUTFLOW ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR,
AND WARM (28-29 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION
IS PLACED WITH HIGH CONFIDENCE BASED ON THE ANIMATED MSI AND
EXTRAPOLATION FROM THE MENTIONED GMI MICROWAVE IMAGE. THE INITIAL
INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: 260205Z METOP-C SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   APRF: T3.5 - 55 KTS
   DEMS: T3.5 - 55 KTS
   CIMSS SATCON: 57 KTS AT 260202Z
   CIMSS ADT: 55 KTS AT 260600Z
   CIMSS DPRINT: 51 KTS AT 260600Z
   CIMSS DMINT: 59 KTS AT 260504Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 FORECAST TO CONTINUE TRACKING
WESTWARD THROUGH TAU 48. AN INCOMING LONGWAVE TROUGH WILL BEGIN
BREAKING DOWN THE CURRENT STEERING RIDGE WITHIN THE NEXT 12 HOURS,
BUT A SECOND STR WILL FOLLOW AND BUILD TO THE SOUTH OF THE SYSTEM,
ALLOWING FOR THE FURTHER WESTWARD TRACK. NEAR TAU 72, 27S WILL
START TO ROUND THE NORTHWESTERN PERIPHERY OF THE SECOND STR AND
WILL BEGIN ITS POLEWARD TURN. REGARDING INTENSITY, 27S IS FORECAST
TO CONTINUE INTENSIFYING THROUGH TAU 72 TO A PEAK OF AROUND 90 KTS.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE, WITH LOW
SHEAR, AMPLE MOISTURE, AND WARM SEA SURFACE TEMPERATURES. AFTER TAU
72, SEA SURFACE TEMPERATURES WILL BEGIN TO COOL AND SHEAR IS
EXPECTED TO INCREASE, CAUSING WEAKENING THROUGH THE REMAINDER OF
THE FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE TRACK OF 27S WITH A MERE 50 NM CROSS-TRACK SPREAD AT
TAU 72, WHICH OPENS UP TO 220 NM AT TAU 120. ALONG-TRACK SPREAD HAS
ALSO LESSENED COMPARED TO THE PREVIOUS MODEL RUNS. AS A RESULT, THE
JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE THROUGH TAU 72
AND MEDIUM CONFIDENCE THEREAFTER. INTENSITY GUIDANCE, ON THE OTHER
HAND, REMAINS IN EXTREMELY POOR AGREEMENT. FRIA, A RAPID
INTENSIFICATION AID IS TRIGGERING, SUGGESTING AN INTENSITY OF 85
KTS AT TAU 24. HAFS-A AND HWRF PAINT TWO COMPLETELY DIFFERENT
PICTURES. HAFS-A SHOWS A PEAK INTENSITY OF AROUND 120 KTS AT TAU
72, WHILE HWRF SHOWS AN INTENSITY OF AROUND 45 KTS AT THE SAME
TIME. COAMPS-TC ALSO DEPICTS WEAKENING AFTER TAU 12, WITH AN
INTENSITY OF AROUND 45 KTS AT TAU 72 AS WELL. THE ECMWF ENSEMBLE
HAS MANY MEMBERS THAT REACH 80 KTS OR MORE, WHILE THE GFS ENSEMBLE
HAS NO MEMBERS REACHING HIGHER THAN 70 KTS, ADDING TO THE DISPARITY
BETWEEN MODELS. THE JTWC INTENSITY FORECAST IS PLACED ABOVE
CONSENSUS DUE TO THE EXPECTED FAVORABLE ENVIRONMENT AND THE QUICK
IMPROVEMENT OF THE STRUCTURE OVER THE PAST 24 HOURS, AIDING IN THE
VERIFICATION OF HAFS-A. 

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