WDXS31 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 22S (HORACIO) WARNING
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.6S 75.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 536 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) IMAGERY REVEALS TROPICAL CYCLONE
(TC) 22S (HORACIO) WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) AND CONVECTION OFFSET TO THE SOUTHWEST. A 201709Z
METOP-C ASCAT PASS REVEALED 20-25 KNOT WINDS WITHIN THE NORTHERN
SEMICIRCLE AND 30-35 KNOT WINDS PRIMARILY CONFINED TO THE
SOUTHWESTERN QUADRANT. THE ASCAT ALSO SHOWED THAT THE CENTER IS
STILL NOT WELL-DEFINED WITH A BROAD REGION OF WEAK WINDS NEAR THE
CENTER. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED
THE WIND MINIMUM REGION OF THE ASCAT. THE INITIAL INTENSITY OF 35
KTS IS PLACED WITH HIGH CONFIDENCE BASED ON THE SAME ASCAT PASS.
AGENCY DVORAK AND CIMSS ADT ESTIMATES INDICATE A HIGHER INTENSITY,
BUT ARE ANALYZED TO BE OVERESTIMATING. THE DPRINT ESTIMATE OF 31 KTS
APPEARS TO BE MORE REPRESENTATIVE OF THE CURRENT STRUCTURE.
ENVIRONMENTAL ANALYSIS INDICATES THAT TC 22S IS IN A FAVORABLE
ENVIRONMENT CHARACTERIZED BY STRONG OUTFLOW ALOFT, LOW (10-15 KTS)
VERTICAL WIND SHEAR, AND WARM (28-29 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: 201709Z METOP-C ASCAT SCATTEROMETER DATA

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

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   FMEE: T3.0 - 45 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS ADT: 53 KTS AT 201800Z
   CIMSS AIDT: 42 KTS AT 201800Z
   CIMSS D-PRINT: 31 KTS AT 201800Z

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

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE INITIAL INTENSITY HAS BEEN DROPPED
TO 35 KTS, CAUSING THE NEAR-TERM INTENSITY FORECAST TO BE LOWER.

FORECAST DISCUSSION: TC 22S IS FORECAST TO TRACK WEST-SOUTHWESTWARD,
ALONG THE NORTHWESTERN PERIPHERY OF THE STR TO THE SOUTHEAST
THROUGH TAU 72. NEAR TAU 72, THE SYSTEM IS EXPECTED TO TURN
SOUTHWARD AS IT BEGINS TO ROUND THE RIDGE AXIS. AROUND TAU 96, 22S
WILL INITIATE A SOUTHEASTWARD TURN AS IT TRAVERSES THE SOUTHWESTERN
PERIPHERY OF THE STR. EXTRATROPICAL TRANSITION IS FORECAST TO BEGIN
NEAR TAU 120 AS IT STARTS TO INTERACT WITH THE UPPER-LEVEL JET.
TRANSITION TO AN EXTRATROPICAL CYCLONE IS EXPECTED TO COMPLETE
OUTSIDE THE 5-DAY FORECAST PERIOD. REGARDING INTENSITY, 22S IS
FORECAST TO STEADILY INTENSIFY OVER THE NEXT 72 HOURS DUE TO THE
PERSISTENCE OF THE FAVORABLE ENVIRONMENT. NEAR TAU 48, POLEWARD
OUTFLOW IS EXPECTED TO STRENGTHEN DUE TO THE INTERACTION WITH AN
INCOMING MAJOR SHORTWAVE TROUGH. THIS WILL ALLOW FOR A POTENTIALLY
RAPID RATE OF INTENSIFICATION THROUGH TAU 72. AFTER TAU 72,
NORTHWESTERLY SHEAR WILL BEGIN TO INCREASE AND SEA SURFACE
TEMPERATURES WILL DECREASE, CAUSING 22S TO WEAKEN THROUGH THE
REMAINDER OF THE FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN BETTER
AGREEMENT THIS MODEL RUN, WITH A CROSS-TRACK SPREAD OF 100 NM
AT TAU 72 AND 200 NM AT TAU 120. THE GOOGLE DEEPMIND ENSEMBLE
MEAN HAS BECOME THE EASTERNMOST MODEL WHILE THE GFS ENSEMBLE
MEAN IS THE WESTERNMOST. THE JTWC TRACK FORECAST IS PLACED CLOSE
TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE THROUGH TAU 72
AND MEDIUM CONFIDENCE THEREAFTER. INTENSITY GUIDANCE GENERALLY
AGREES ON INTENSIFICATION THROUGH TAU 72 FOLLOWED BY WEAKENING.
PEAK INTENSITIES RANGE FROM 110 KTS (HAFS-A) AND 80 KTS (GFS).
THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE CONSENSUS WITH
OVERALL MEDIUM CONFIDENCE.

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