WDXS31 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) WARNING 
NR 
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.5S 70.5E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 187 NM SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING
CONVECTION ASSOCIATED WITH A LOW-LEVEL CIRCULATION CENTER (LLCC)
THAT IS BECOMING INCREASINGLY RAGGED AND DISORGANIZED. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A MICROWAVE EYE
THAT IS STILL EVIDENT IN A 190016Z GMI 37GHZ IMAGE. 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, WITH DRY
AIR BEGINNING TO ENTRAIN INTO THE WESTERN PORTION OF THE
CIRCULATION, SO THE OVERALL ENVIRONMENT IS 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
   FMEE: T3.0 - 45 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS SATCON: 49 KTS AT 182058Z
   CIMSS ADT: 45 KTS AT 182100Z

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

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 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. OVER THE PAST SEVERAL HOURS, THE CONVECTIVE SIGNATURE HAS
ERODED, SUGGESTING THAT VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT
IS TAKING ITS TOLL. THE OFFICIAL FORECAST IS CONTINGENT UPON TC 19S
MAINTAINING ENOUGH VERTICAL COHERENCY. ASSUMING THE SYSTEM DOES NOT
DISSIPATE SOONER THAN EXPECTED, GRADUAL WEAKENING IS FORECAST AS
VERTICAL WIND SHEAR INCREASES, SEA SURFACE TEMPERATURES COOL, AND
DRY AIR ENTRAINS ALONG THE PATH OF THE FORECAST TRACK. REGARDLESS,
AS IT BECOMES A MORE SHALLOW SYSTEM, TC 19S WILL AGAIN TURN TOWARD
THE SOUTHWEST BEYOND TAU 96 IN RESPONSE TO THE L0W-LEVEL STEERING
FLOW, WITH DISSIPATION OVER WATER EXPECTED SHORTLY THEREAFTER.

MODEL DISCUSSION: THE GLOBAL MODELS ALL CONTINUE TO SUGGEST AN
S-SHAPED TRACK SCENARIO, BUT WITH INCREASING UNCERTAINTY. GIVEN THE
COMPETING INFLUENCES OF THE STEERING RIDGES, COMBINED WITH THE
VERTICAL WIND SHEAR BEGINNING TO IMPACT THE VERTICAL COHERENCY OF
THE TC 19S VORTEX, MODEL SPREAD IS INCREASING. THE NAVGEM REMAINS
THE WESTERNMOST OUTLIER, WITH THE GALWEM SUGGESTING 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 OVER 300 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. THAT SAID, IT IS POSSIBLE THAT THE RECENT
DETERIORATION OF THE VORTEX WILL ACCELERATE THE WEAKENING BEYOND
CURRENTLY FORECAST, WITH DISSIPATION OCCURRING SOONER THAN
ANTICIPATED.

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