WDXS31 PGTW 102100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 14S (FOURTEEN) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.9S 76.0E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 457 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT AND SYMMETRICAL CENTRAL DENSE OVERCAST (CDO) OBSCURING THE
LOW LEVEL CIRCULATION CENTER (LLCC). DEEP CONVECTION ASSOCIATED
WITH THE CDO CONTINUES TO PULSE, CREATING STRONG GRAVITY WAVES
WHICH CAN BE SEEN EMANATING OUTWARDS IN ANIMATED WATER VAPOR
IMAGERY. CIMSS ATMOSPHERIC MOTION VECTORS (AMV) SUGGEST THE
UPPER-LEVEL EASTERLIES ARE SPLITTING UPSTREAM OF THE CDO, REDUCING
LOCALIZED SHEAR IN THE VICINITY OF THE LLCC. THE A 101539Z ASCAT-B
BULLSEYE PASS REVEALED THE LLCC POSITIONED ON THE EASTERN EDGE OF
THE CDO, WITH WINDS UP TO 40-45 KNOTS IN THE SOUTHWESTERN QUADRANT.
THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN
EXTRAPOLATION OF THE LLCC SEEN IN THE SCATTEROMETER PASS. THE
INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, BIASED HIGHER
THAN THE PGTW AND FMEE T2.5 DVORAK CURRENT INTENSITY ESTIMATES
BASED ON THE ASCAT DATA. ENVIRONMENTAL CONDITIONS ARE FAVORABLE FOR
INTENSIFICATION, CHARACTERIZED BY WARM SSTS, LOW VWS AND
STRENGTHENING POLEWARD OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) COMPLEX POSITIONED TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS D-PRINT: 34 KTS AT 102000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 14S (FOURTEEN) IS
FORECAST TO TRACK SOUTH-SOUTHEASTWARD ALONG THE WESTERN FLANK OF A
STR COMPLEX SITUATED TO THE EAST. BY TAU 36, THE SYSTEM WILL SLOW
DOWN SIGNIFICANTLY AND BEGIN TO TURN SOUTHWESTWARD, IN RESPONSE TO
THE DEVELOPMENT OF AN EXTENSION OF A RIDGE TO THE SOUTH OF THE
SYSTEM. AFTER TAU 48, THE SYSTEM WILL EXPERIENCE ADDITIONAL SLOWING
AS THE RIDGE TO THE SOUTH RAPIDLY ERODES AND THE SYSTEM MOVES INTO
A COMPETING STEERING PATTERN, WITH RIDGING TO THE EAST AND WEST AND
A TROF TO THE SOUTH. TC 14S IS FORECAST TO STEADILY INTENSIFY
THROUGH TAU 48, UP TO A PEAK OF 70 KNOTS, UNDER FAVORABLE
ENVIRONMENTAL CONDITIONS OF LOW DEEP-LAYER SHEAR, WARM SSTS AND
GOOD POLEWARD OUTFLOW. WHILE ASSESSED AS A LOW PROBABILITY AT THIS
TIME, THE EXCEPTIONALLY SMALL NATURE OF THE INNER-CORE SUPPORTS
RAPID CHANGES IN INTENSITY AND RAPID INTENSIFICATION (RI) IS
POSSIBLE IN THE NEAR-TERM, ESPECIALLY IF THE VORTEX CAN RAPIDLY
ALIGN VERTICALLY. AFTER PEAKING IN INTENSITY AROUND TAU 48,
DEEP-LAYER NORTHWESTERLY SHEAR IS FORECAST TO IMPACT THE SYSTEM,
LEADING TO A SLOW BUT STEADY WEAKENING THROUGH THE REMAINDER OF THE
FORECAST. AS THE SYSTEM WEAKENS AND THE VORTEX SHALLOWS OUT, IT
WILL TURN ONTO A WESTWARD TRACK, ALONG THE NORTHERN FLANK OF AN
EXTENSIVE RIDGE TO THE SOUTH. 

MODEL DISCUSSION: THROUGH THE FIRST 48 HOURS OF THE FORECAST,
DETERMINISTIC, ENSEMBLE AND ARTIFICIAL INTELLIGENCE (AI) MODELS ARE
IN OVERALL AGREEMENT ON THE SOUTHEASTWARD TRACK MOTION, BUT EXHIBIT
A CROSS-TRACK SPREAD OF APPROXIMATELY 135NM. THE AI MODELS (AICN,
FGNE, AIFS) DEPICT A STRAIGHT TRACK TOWARDS THE SOUTH-SOUTHEAST,
WHILE THE DETERMINISTIC AIDS OUTLINE A GENTLY CURVING TRACK MORE
TOWARDS THE SOUTH OR SOUTHWEST. AFTER TAU 48, THE MODELS BEGIN TO
DIVERGE SIGNIFICANTLY. THE GALWEM PERFORMS A CLOCKWISE LOOP TO
NORTH, THE AI MODELS TRACK NORTHWESTWARD, THE GFS TRACK WESTWARD AT
A PACE THAT FAR OUTPACES THE OTHER GUIDANCE, WHILE THE ECMWF BRINGS
UP THE REAR, VERY SLOWLY DRIFTING WESTWARD AFTER TAU 72. THE
RESULTING CROSS-TRACK SPREAD EXCEEDS 400NM, WHILE THE ALONG-TRACK
UNCERTAINTY EXCEEDS 250NM. ENSEMBLE TRACK GUIDANCE IS IN BETTER
AGREEMENT, WITH BOTH THE GEFS AND ECEPS DEPICTING A RELATIVELY
NARROW ENVELOPE, THOUGH THE GEFS IS SIGNIFICANTLY FASTER THAN THE
ECEPS. THE JTWC FORECAST IS POSITIONED CLOSE TO THE MULTI-MODEL
CONSENSUS MEAN THROUGH THE FORECAST PERIOD, WITH MEDIUM TO LOW
CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM
WILL STEADILY INTENSIFY TO A PEAK OF 60-80 KNOTS BETWEEN TAU 48 AND
TAU 60 FOLLOWED BY SLOW WEAKENING. AS MENTIONED ABOVE, THE RIDE RI
AID IS TRIPPED, WHICH SUPPORTS A PEAK INTENSITY OF 105 KNOTS BY TAU
48. THE JTWC FORECAST IS PLACED NEAR THE HAFS-A TRACE WITH MEDIUM
CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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