WDXS31 PGTW 312100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (ELEVEN) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.2S 106.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 555 NM EAST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 11S WITH IMPROVED PERSISTENT CENTRAL CONVECTION THAT IS NOW
CONFINED TO A SMALL POCKET OVER THE LOW-LEVEL CIRCULATION CENTER
(LLCC). CLOUD TOPS WITHIN THE ENVIRONMENTAL ANALYSIS INDICATES THAT
11S IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY
MODERATE POLEWARD OUTFLOW ALOFT, LOW (10-15 KTS) VERTICAL WIND
SHEAR, AND WARM (28-29 C) SEA SURFACE TEMPERATURES. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED EIR
IMAGERY. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE PGTW FIX OF T2.0 AND AN EARLY CIMSS DPRINT
ESTIMATE OF 33 KTS. ADDITIONALLY, A PARTIAL 311444Z METOP-C ASCAT
PASS SHOWED 30-35 KTS WITHIN THE EASTERN PERIPHERY.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: EASTERN PERIPHERY OF A LOW TO MID-LEVEL
NEAR-EQUATORIAL RIDGE (NER) POSITIONED TO THE WEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   CIMSS D-PRINT: 33 KTS AT 312000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 11S IS FORECAST TO TRACK SOUTHEASTWARD,
ALONG THE EASTERN PERIPHERY OF THE LOW TO MID-LEVEL NER TO THE WEST
THROUGH TAU 48. NEAR TAU 48, THE STEERING MECHANISM WILL SWITCH TO A
LARGE SUBTROPICAL RIDGE TO THE SOUTH OF THE SYSTEM, CAUSING 11S TO
TURN SHARPLY WESTWARD. A WESTWARD TRACK IS THEN EXPECTED TO PERSIST
THROUGH THE REMAINDER OF THE FORECAST PERIOD. IN TERMS OF
INTENSITY, 11S IS FORECAST TO GRADUALLY INTENSIFY THROUGH TAU 36 AS
SHEAR REMAINS LOW. NEAR TAU 36, NORTHWESTERLY SHEAR IS EXPECTED TO
QUICKLY INCREASE TO OVER 20 KTS, CAUSING 11S TO WEAKEN AS IT MAKES
THE WESTWARD TURN. IN ADDITION TO THE INCREASING SHEAR, DRY AIR
ENTRAINMENT FROM THE WEST IS EXPECTED TO BEGIN IMPACTING THE
VORTEX, FURTHER AIDING IN THE WEAKENING TREND. 11S IS FORECAST TO
WEAKEN BELOW 35 KTS AROUND TAU 96. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 48, WITH THE EXCEPTION OF NAVGEM, WHICH
TRACKS THE VORTEX MUCH FURTHER EASTWARD THAN THE REMAINDER OF
GUIDANCE. DISCOUNTING NAVGEM, THERE IS A 70 NM CROSS-TRACK SPREAD
AT TAU 48. AFTER TAU 48, MODEL START TO DIVERGE DUE TO DIFFERING
INTERACTIONS WITH THE STEERING MECHANISM SWITCH. GFS AND THE GFS
ENSEMBLE MEAN ARE THE TWO FASTEST MODELS DURING THROUGHOUT THE
WESTWARD TURN. ON THE OTHER HAND, ECMWF IS THE SLOWEST TO TURN THE
SYSTEM. ALONG-TRACK SPREAD AT TAU 96 INCREASES TO OVER 400 NM WITH
THE GFS BEING FAR AND AWAY THE FASTEST MODEL. THE JTWC TRACK
FORECAST IS PLACED NEAR THE CONSENSUS THROUGH TAU 72 AND THEN
CLOSER TO THE GOOGLE DEEPMIND THEREAFTER. INTENSITY GUIDANCE
GENERALLY AGREES ON MARGINAL INTENSIFICATION THROUGH TAU 36 AND
WEAKENING AFTERWARD. COAMPS-TC (GFS BASED) HAS A MUCH SHARPER
WEAKENING TREND AFTER TAU 36, DROPPING THE INTENSITY TO JUST 15 KTS
AT TAU 96. THE JTWC INTENSITY FORECAST IS PLACED NEAR THE
MULTI-MODEL CONSENSUS 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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