WDXS31 PGTW 212100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 22S (HORACIO) WARNING 
NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.9S 71.8E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 589 NM SOUTH OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 22S (HORACIO) WITH A PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION (LLCC) THAT HAS IMPROVED DEFINITION AND IS NOW FURTHER
EMBEDDED UNDERNEATH THE DEEP CONVECTION. HOWEVER, EASTERLY SHEAR
HAS CONTINUED TO CAUSE THE VORTEX TO BE TILTED WESTWARD WITH HEIGHT
AND CONVECTIVE ACTIVITY TO BE SLIGHTLY OFFSET FROM THE LLCC. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
EXPOSED LOW-LEVEL CLOUDS WITHIN THE EASTERN SEMICIRCLE IN ANIMATED
EIR IMAGERY. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES RANGING FROM
T3.0-3.5 AND THE CIMSS ESTIMATES LISTED BELOW. ENVIRONMENTAL
ANALYSIS INDICATES THAT 22S CONTINUES TO BE PLACED WITHIN A
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD
OUTFLOW ALOFT, MODERATE (15-20 KTS) EASTERLY VERTICAL WIND SHEAR,
SLIGHT DRY AIR ENTRAINMENT, AND WARM (28-29 C) SEA SURFACE
TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   FMEE: T3.5 - 55 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS ADT: 47 KTS AT 211800Z
   CIMSS AIDT: 40 KTS AT 211800Z
   CIMSS D-PRINT: 37 KTS AT 211800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: SLIGHT DRY AIR ENTRAINMENT WITHIN THE
NORTHEASTERN QUADRANT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TC 22S IS FORECAST TO TRACK
WEST-SOUTHWESTWARD, ALONG THE NORTHWESTERN PERIPHERY OF THE STR TO
THE SOUTHEAST, THROUGH TAU 48. NEAR TAU 48, 22S WILL BEGIN TURNING
SOUTHWARD AS IT ROUNDS THE WESTERN EXTENT OF THE STR. 22S WILL THEN
TURN SOUTH-SOUTHEASTWARD AROUND TAU 72, AS IT ATTEMPTS TO ROUND THE
RIDGE AXIS. HOWEVER, A SMALL RIDGE IS EXPECTED TO BRIEFLY BUILD TO
THE SOUTH OF THE VORTEX NEAR TAU 96, HALTING THE POLEWARD TRACK AND
PUSHING 22S SOUTH-SOUTHWESTWARD THROUGH TAU 120. EXTRATROPICAL
TRANSITION IS FORECAST TO BEGIN AT TAU 120 AS THE SYSTEM FURTHER
INTERACTS WITH THE STRONG UPPER-LEVEL WESTERLIES AND ENTERS 22-23 C
WATERS. EXTRATROPICAL TRANSITION IS FORECAST TO FULLY COMPLETE JUST
OUTSIDE OF THE FORECAST PERIOD. IN TERMS OF INTENSITY, 22S IS
FORECAST TO GRADUALLY INTENSIFY THROUGH TAU 24 AS EASTERLY SHEAR
AND DRY AIR CONTINUE TO HAVE AN IMPACT ON THE VORTEX. AFTER TAU 24,
SHEAR IS EXPECTED TO LESSEN AND POLEWARD OUTFLOW IMPROVE, ALLOWING
FOR 22S TO RAPIDLY INTENSIFY THROUGH 48 TO AROUND 95 KTS. THE RAPID
INTENSIFICATION (RI) IS EXPECTED TO PERSIST THROUGH TAU 60, LIKELY
WHEN THE ACTUAL PEAK INTENSITY WILL OCCUR (THOUGH NOT DIRECTLY
REFLECTED IN THE FORECAST DUE TO TEMPORAL RESTRICTIONS). AFTER TAU
60, NORTHWESTERLY SHEAR WILL QUICKLY INCREASE AND SEA SURFACE
TEMPERATURES WILL DROP CAUSING 22S TO WEAKEN THROUGH THE REMAINDER
OF THE FORECAST PERIOD. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 72 WITH A CROSS-TRACK SPREAD OF 130 NM AT
THAT TIME. AFTER TAU 72, MODELS DIVERGE DUE TO DIFFERING
INTERACTIONS WITH THE SMALL STR THAT BUILDS TO THE SOUTH OF THE
SYSTEM. CROSS-TRACK SPREAD AT TAU 120 INCREASES TO AROUND 360 NM
WITH THE GFS ENSEMBLE MEAN BEING THE WESTERNMOST MODEL AND THE
ECMWF DETERMINISTIC BEING THE EASTERNMOST. THE JTWC TRACK FORECAST
IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE
THROUGH TAU 72 AND THEN CLOSER TO THE GOOGLE DEEPMIND AND ECMWF
TRACKERS THROUGH TAU 120 WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE
IS IN GENERALLY GOOD AGREEMENT ON STEADY INTENSIFICATION THROUGH
TAU 24 AND THEN A MORE RAPID RATE OF INTENSIFICATION THROUGH TAU
60. OF NOTE, A COUPLE RI AIDS TRIGGERED THIS RUN (DTOP AND RIDE).
HWRF AND SHIPS ARE THE TWO OUTLIERS, WHICH SUGGEST A LOWER PEAK OF
AROUND 65-75 KTS. ON THE OTHER HAND, HAFS-A AND COAMPS-TC (ALONG
WITH THE RI AIDS) SUGGEST A PEAK OF CLOSER TO 105-120 KTS. THE JTWC
INTENSITY FORECAST IS PLACED ABOUT 5 KTS HIGHER THAN THE CONSENSUS
THROUGHOUT THE FORECAST PERIOD 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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