WDXS31 PGTW 302001
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING 
NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.7S 87.9E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 813 NM SOUTHWEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
HEAVILY SHEARED TROPICAL CYCLONE (TC) 27S (COURTNEY) AS IT IS
CURRENTLY ROUNDING THE AXIS OF A STR TO THE EAST AND BEGINNING TO
TRANSIT SOUTHWARD. THE LOW-LEVEL CIRCULATION (LLCC) IS CURRENTLY
STILL PARTIALLY OBSCURED, BUT THE DRAMATICALLY INCREASING VERTICAL
WIND SHEAR (VWS) IS PUSHING THE CONVECTION SOUTHEASTWARD. 
ENVIRONMENTAL ANALYSIS REVEALS HIGHLY UNFAVORABLE ENVIRONMENT
DOMINATED BY HIGH (25-30 KTS) VWS, COOL (25-26 C) SEA SURFACE
TEMPERATURES, AS WELL AS DEEP-LAYER DRY AIR BEGINNING TO ERODE THE
VORTEX OF THE SYSTEM. POLEWARD OUTFLOW CHANNEL REMAINS STRONG AND
HELPS DISTRIBUTE THE CONVECTION POLEWARD AND EASTWARD. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE EXPOSED
NORTHERN SEMICIRCLE OF THE LLCC VISIBLE IN THE ANIMATED EIR LOOP.
THE INITIAL INTENSITY OF 70 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON DECREASING AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES 
LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   DEMS: T4.5 - 77 KTS
   FIMP: T4.5 - 77 KTS
   CIMSS SATCON: 66 KTS AT 301715Z
   CIMSS ADT: 67 KTS AT 301815Z
   CIMSS AIDT: 62 KTS AT 301815Z
   CIMSS D-MINT: 64 KTS AT 301249Z
   CIMSS D-PRINT: 43 KTS AT 301815Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 25-30 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT WITHIN THE NORTHWESTERN
PORTION OF THE CIRCULATION

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: HOSTILE ENVIRONMENT IS RESULTING IN
QUICKER WEAKENING AND TRUNCATION OF THE FORECAST TO 48 HOURS.

FORECAST DISCUSSION: TC 27S IS FORECAST TO TRACK ALONG THE
SOUTHWESTERN QUADRANT OF A STR LOCATED TO THE EAST OVER THE NEXT 36
HOURS. BETWEEN TAU 24 AND 48, VWS IS FORECAST TO INCREASE TO OVER
65 KTS, LEADING TO COMPLETE DECAPITATION OF THE DEEP CONVECTION AND
SHALLOWING OF THE SYSTEM. AT THE SAME TIME, TC COURTNEY WILL
APPROACH COOLER WATERS, WITH SEA SURFACE TEMPERATURES BELOW 25 C.
SIMULTANEOUSLY, THE CORE OF THE SYSTEM WILL BECOME COMPLETELY
SURROUNDED BY DRY AIR, LEADING TO RAPID WEAKENING AND DISSIPATION
BY TAU 48. AROUND THAT TIME, REMNANTS OF TC 27S WILL BE STEERED
WESTWARD BY A STRONG, LOW-LEVEL RIDGE CENTERED TO THE SOUTH OF
THE REMAINING CIRCULATION.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN FAIR AGREEMENT 
IN REGARD TO THE TRACK, WITH CROSS-TRACK SPREAD OF 55 NM AT TAU 24, 
INCREASING TO 185 NM BY TAU 48. NAVGEM AND DETERMINISTIC GFS GUIDANCE 
ARE THE OUTLIERS, WITH THE FORMER PREDICTING SOUTHWESTWARD TRACK, 
WHILE THE LATTER IS MORE CONSISTENT WITH THE MULTI-MODEL CONSENSUS, 
REFLECTING THE DOMINANT STEERING BY THE STR TO THE EAST AND TAKING THE 
SYSTEM ON A SOUTHEASTWARD TRACK. JTWC TRACK FORECAST IS LAID CLOSE TO 
THE MULTI-MODEL CONSENSUS, LEANING SLIGHTLY CLOSER TO THE GFS 
SOLUTION, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD 
AGREEMENT, WITH ALL AVAILABLE MODELS INDICATING STEADY WEAKENING, 
REFLECTING HOSTILE ENVIRONMENT. STORM-CENTERED CROSS SECTIONS FROM 
BOTH HAFS AND DETERMINISTIC GFS BOTH AGREE THAT THE SYSTEM WILL BECOME 
VOID OF DEEP CONVECTION BETWEEN TAUS 24 AND 36. JTWC INTENSITY 
FORECAST IS ASSESSED WITH HIGH CONFIDENCE, WITH CLOSE PROXIMITY TO THE
MULTI-MODEL CONSENSUS RESULT, SLIGHTLY BELOW THE GFS DETERMINISTIC
GUIDANCE AND CLOSE TO HAFS DISSIPATION TIMELINE.

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