WDXS31 PGTW 182100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) WARNING 
NR 
019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.4S 70.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 168 NM SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS RAGGED
CONVECTION FLARING NEAR A LOW-LEVEL CIRCULATION CENTER (LLCC). A
181410Z SSMIS 91GHZ MICROWAVE PASS INDICATES THAT MOST OF THE DEEP
CONVECTION IS WRAPPING AROUND THE SOUTHWESTERN SIDE OF THE LLCC.
THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
THE AFOREMENTIONED MICROWAVE IMAGE AND ANIMATED EIR. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF
SUBJECTIVE AGENCY DVORAK ESTIMATES RANGING FROM T2.5 TO T3.0
COMBINED WITH SATCON. WARM SEA SURFACE TEMPERATURES ARE OFFSET BY
MODERATE TO STRONG VERTICAL WIND SHEAR AND WEAK OUTFLOW, SO THE
OVERALL ENVIRONMENT IS MARGINALLY UNFAVORABLE FOR DEVELOPMENT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE WEST AND
A NEAR EQUATORIAL RIDGE
(NER) TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   DEMS: T2.5 - 35 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS SATCON: 45 KTS AT 181529Z
   CIMSS ADT: 35 KTS AT 181500Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 30+ KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK POLEWARD

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: TROPICAL CYCLONE 19S (FABIEN) CONTINUES TO
TRACK SLOWLY WEST-SOUTHWESTWARD IN A WEAK STEERING ENVIRONMENT
BETWEEN A SUBTROPICAL RIDGE (STR) TO THE WEST AND A NEAR EQUATORIAL
RIDGE (NER) TO THE NORTHEAST. THE SYSTEM IS EXPECTED TO TRACK
SLOWLY TOWARD THE WEST-SOUTHWEST THROUGH TAU 24 TO 36. A BREAK IN
THE STR WILL THEN ALLOW THE SYSTEM TO TURN TOWARD SOUTHEAST THROUGH
TAU 72. AS VERTICAL WIND SHEAR INCREASES, SEA SURFACE TEMPERATURES
COOL, AND DRY AIR ENTRAINS ALONG THE PATH OF THE FORECAST TRACK, TC
19S IS FORECAST TO GRADUALLY WEAKEN. AS IT BECOMES A MORE SHALLOW
SYSTEM, IT WILL AGAIN TURN TOWARD THE SOUTHWEST BEYOND TAU 96 IN
RESPONSE TO THE L0W-LEVEL STEERING FLOW.

MODEL DISCUSSION: THE GLOBAL MODELS ALL SUGGEST AN S-SHAPE TRACK
SCENARIO, GIVEN THE COMPETING INFLUENCES OF THE STEERING RIDGES.
THE NAVGEM IS THE WESTERNMOST OUTLIER, AND THE GALWEM SUGGESTS A
CLOCKWISE LOOP, BUT OTHERWISE, MOST MODELS INDICATE A TURN TOWARD
THE SOUTHEAST AND THEN BACK TOWARD THE SOUTHWEST. HOWEVER, THE
TIMING OF THE TURNS ARE HIGHLY UNCERTAIN, AND THE OVERALL SPREAD IN
TRACK GUIDANCE IS 400 NM BY TAU 120. THE JTWC FORECAST STAYS CLOSE
TO CONSENSUS BUT IS LOW CONFIDENCE THROUGH THE FORECAST PERIOD.
INTENSITY GUIDANCE IS IN GENERAL AGREEMENT, CALLING FOR A
RELATIVELY STEADY-STATE INTENSITY FOLLOWED BY A GRADUAL WEAKENING
TREND, SO THE INTENSITY FORECAST CONFIDENCE IS HIGH THROUGH TAU 72
AND MEDIUM BEYOND.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: HIGH
   INTENSITY 72-120 HR: MEDIUM//
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