WDXS31 PGTW 031500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FYTIA) WARNING NR 
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.8S 54.5E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 203 NM SOUTH-SOUTHWEST OF ST DENIS
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SYSTEM 
UNDERGOING RAPID VORTEX DECOUPLING, WITH THE LOW LEVEL CIRCULATION 
CENTER (LLCC) EMERGING OUT FROM UNDER THE CONVECTIVE ENVELOPE OVER 
THE PAST FEW HOURS DUE TO PERSISTENT STRONG NORTHWESTERLY VERTICAL 
WIND SHEAR (VWS). A 031012Z NOAA-20 ATMS 89GHZ MICROWAVE IMAGE 
REVEALED THE LLCC ALREADY BEGINNING TO DECOUPLE, WITH SHALLOW BANDING 
FEATURES WRAPPING INTO A SHALLOW VORTEX. ANIMATED WATER VAPOR IMAGERY 
REVEALS A DEEP UPPER-LEVEL TROUGH TO THE SOUTHWEST MAINTAINING ROBUST 
POLEWARD OUTFLOW; HOWEVER, THE UPSTREAM PATTERN INDICATES IMPENDING 
SUBSIDENCE ALOFT AND INCREASED SHEAR IS INBOUND. THE INITIAL POSITION 
IS ASSESSED WITH HIGH CONFIDENCE BASED ON A EXPOSED LLCC IN THE 
ANIMATED MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM 
CONFIDENCE, HEDGED TOWARDS THE HIGHER END OF THE AVAILABLE SUBJECTIVE 
AND OBJECTIVE INTENSITY ESTIMATES OUTLINED BELOW. ENVIRONMENTAL 
CONDITIONS ARE DETERIORATING RAPIDLY AND ARE CHARACTERIZED AS 
UNFAVORABLE, DRIVEN BY HIGH NORTHWESTERLY SHEAR, SUB-OPTIMAL SSTS, 
AND PRONOUNCED MID-LEVEL DRY AIR INTRUSION FROM THE NORTHWEST.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR). 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   FMEE: T3.5 - 55 KTS
   CIMSS SATCON: 48 KTS AT 031200Z
   CIMSS ADT: 57 KTS AT 031200Z
   CIMSS AIDT: 51 KTS AT 031200Z
   CIMSS D-MINT: 44 KTS AT 031013Z
   CIMSS D-PRINT: 41 KTS AT 031200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: PRONOUNCED MID-LEVEL DRY AIR INTRUSION. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 19S IS TRACKING
SOUTHEAST ALONG THE GRADIENT BETWEEN THE MID-LEVEL STR TO THE
NORTHEAST AND THE TROF TO THE SOUTHWEST. THROUGHOUT THE FORECAST 
PERIOD, THE SYSTEM WILL DECELERATE AS THE VORTEX SHALLOWS AND BECOMES 
EMBEDDED INTO A WEAKER STEERING GRADIENT BETWEEN TWO REGIONS OF 
LOWER-LEVEL RIDGING. GLOBAL DETERMINISTIC MODELS EXHIBIT SIGNIFICANT 
VARIANCE REGARDING THE TRANSLATIONAL SPEED OF TC 19S, ESPECIALLY 
BEYOND TAU 24, CONTRIBUTING TO INCREASED UNCERTAINTY IN THE EXTENDED 
FORECAST PERIOD. THE GFS DEPICTS A MUCH WEAKER STEERING GRADIENT 
RESULTING IN A STAGNANT TRACK WHILE THE ECMWF RECURVES TC 19S 
SOUTHWARD INTO THE TROUGH AT A HIGHER VELOCITY. IN TERMS OF INTENSITY, 
THE SYSTEM HAS INITIATED DECOUPLING DUE TO ADVERSE VWS AND DRY AIR 
INTRUSION. BOTH FACTORS ARE FORECAST TO INTENSIFY OVER THE 
NEXT 24 HOURS, LEADING TO A COMPLETE DISRUPTION OF THE VORTEX 
STRUCTURE. THE REMNANT LOW-LEVEL VORTEX WILL GRADUALLY ERODE AS IT 
SIMULTANEOUSLY UNDERGOES SUBTROPICAL TRANSITION (STT). CYCLOLYSIS MAY 
OCCUR PRIOR TO FULL STT, WHICH IS ANTICIPATED BY TAU 48. 

MODEL DISCUSSION: DETERMINISTIC, ENSEMBLE AND ARTIFICIAL INTELLIGENCE 
(AI) MODELS ARE IN GOOD OVERALL AGREEMENT THAT TC 19S WILL TRACK 
SOUTHEASTWARD THROUGH THE FORECAST PERIOD. HOWEVER, CROSS- MODEL 
DISCONTINUITY REMAINS HIGH REGARDING TRACK SPEED, PARTICULARLY 
AFTER TAU 24 WHEN THE GFS AND GEFS DIVERGE FROM THE ECMWF, ECENS, AND 
AI GUIDANCE. THE JTWC FORECAST IS ALIGNED NEAR THE GDM ENSEMBLE MEAN 
THROUGH TAU 36, THEN CONVERGES WITH THE CONSENSUS MEAN AT TAU 48, 
WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE REMAINS BIFURCATED; THE 
GFS AND COTC INDICATE RAPID WEAKENING AB INITIO, WHILE THE HAFS-A 
PROJECTS SLOW WEAKENING TO TAU 24 FOLLOWED BY SPURIOUS INTENSIFICATION 
TO 60 KNOTS BY TAU 60. THIS OUTLIER IS LIKELY ATTRIBUTABLE TO MISS 
MODELED BAROCLINIC FORCING AND IS DEEMED HIGHLY UNLIKELY. THE 
REMAINDER OF THE GUIDANCE DEPICTS A GRADUAL WEAKENING THROUGH TAU 48 
AND THE JTWC FORECAST HEWES TO THIS CONSENSUS WITH MEDIUM CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM//
NNNN