WDXS32 PGTW 032100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (VINCE) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.1S 92.1E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 405 NM SOUTHWEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TIGHTLY
WRAPPING SPIRAL BANDS OF DEEP CONVECTION ASSOCIATED WITH TC 13S
(VINCE). THE LOW-LEVEL CIRCULATION (LLCC) IS FULLY OBSCURED AT THE 
TIME OF THE FORECAST, HOWEVER A 031223Z SAR IMAGE DEPICTS A LOW-LEVEL
REGION OF CALM WINDS, INDICATIVE OF AN EYE FORMATION. ENVIRONMENTAL
CONDITIONS REMAIN MARGINALLY FAVORABLE, WITH WARM (26-27 C) SEA
SURFACE TEMPERATURES AND STRONG UPPER-LEVEL WESTWARD OUTFLOW, WHILE
THE CONVECTION IS PUSHED WESTWARD BY THE MODERATE 15-20 KTS
EASTERLY SHEAR. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE 031223Z SAR EXTRAPOLATION, CONSISTENT WITH
THE CONVECTIVE BANDING WRAPPING. THE INITIAL INTENSITY OF 70 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED ASCAT
PASS, IN CONJUNCTION WITH THE DVORAK AGENCY FIXES AND AUTOMATED
ESTIMATED FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: 031224Z SAR DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) 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: 73 KTS AT 031641Z
   CIMSS ADT: 49 KTS AT 031730Z
   CIMSS AIDT: 57 KTS AT 032000Z
   CIMSS D-PRINT: 85 KTS AT 031800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG WESTWARD

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 13S IS FORECAST TO TRACK
WEST-SOUTHWESTWARD, ALONG THE NORTHWESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE. AS THE ENVIRONMENTAL PARAMETERS ARE PREDICTED TO
REMAIN CONSISTENTLY MARGINALLY FAVORABLE, THE SYSTEM IS EXPECTED TO
MAINTAIN INTENSITY OVER THE NEXT 72 HOURS, FOLLOWED BY A PERIOD OF
SLIGHT INTENSIFICATION. BY TAU 96, TC 13S WILL ENCOUNTER A PATCH OF 
WARMER SEA SURFACE TEMPERATURES. THE STEERING STR TO THE SOUTH IS 
EXPECTED TO WEAKEN WHILE THE DIVERGENCE ALOFT IS FORECAST TO 
INCREASE. 
THE INCREASE IN DIVERGENCE ALOFT WILL IMPROVE THE OUTFLOW, THEREFORE 
THE CURRENT FORECAST CALLS FOR INTENSIFICATION TO 85 KTS BY THE END 
OF 
THE FORECAST PERIOD. HOWEVER, IF THE STR TO THE SOUTH WEAKENS MORE 
THAN FORECASTED AND TC 13S TAKES A MORE SOUTHWARD TRACK, IT WILL 
ENCOUNTER COOLER SSTS, WHICH WILL STALL ITS FURTHER INTENSIFICATION.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGHOUT TAU 96, WITH CROSS-TRACK SPREAD OF 100 NM. PAST TAU 96,
THE GUIDANCE DIVERGES, WITH SOME AIDS (ECMWF, ECENS) SUGGESTING A
MORE SOUTHERLY TRACK, WHILE OTHERS (HAFS, GFS, GEFS) TRACKING MORE
WEST-SOUTHWESTWARD. THOSE SLIGHT DIFFERENCES IN TRACK GUIDANCE LEAD
HOWEVER TO A MUCH MORE SIGNIFICANT SPREAD OF THE INTENSITY GUIDANCE.
MAJORITY OF THE AVAILABLE DETERMINISTIC MODELS SUGGEST AN UPTICK IN
INTENSITY BETWEEN TAUS 72 AND 120, WITH THE MOST SIGNIFICANT
OUTLIER BEING THE HAFS GUIDANCE TAKING THE PEAK INTENSITY AS HIGH
AS 130 KTS. JTWC INTENSITY FORECAST IS THEREFORE ASSESSED WITH
MEDIUM CONFIDENCE THROUGH TAU 72, AND LOW CONFIDENCE THEREAFTER,
THROUGHOUT THE END OF THE FORECAST PERIOD.

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