WDPS31 PGTW 170900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19P (MEGAN)
WARNING NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.0S 137.0E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 386 NM EAST-SOUTHEAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 19P (MEGAN) EXHIBITING A VERY EXPANSIVE CENTRAL
DENSE OVERCAST FEATURE OBSCURING NEARLY ALL OF THE GULF OF
CARPENTARIA AS WELL AS THE STORMS ASSESSED LOW-LEVEL CIRCULATION
CENTER. 170417Z AMSR2 37GHZ AND 89GHZ SATELLITE MICROWAVE IMAGERY
AND RADAR DATA REVEALED THE SYSTEM HAS A COMPLETE EYE STRUCTURE
THAT IS LIKELY BEING COVERED IN VISIBLE IMAGERY DUE TO THE ROBUST
CENTRAL CONVECTION OVER THE PAST SIX HOURS WITH AN ASSESSED POINT
SOURCE ALOFT COLLOCATED OVERHEAD THE LLCC. THE INITIAL POSITION IS 
PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION OF THE 
AFOREMENTIONED AMSR2 SATELLITE MICROWAVE IMAGES AND RADAR DATA. THE 
INITIAL INTENSITY OF 85 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED 
ON THE RISE OF SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES LISTED 
BELOW.

INITIAL WIND RADII BASIS: 170417Z AMSR2 WINDSPEED IMAGE AND SURFACE
OBSERVATIONS

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A WEAK NEAR
EQUATORIAL RIDGE (NER) TO THE EAST. 


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T5.0 - 90 KTS
   CIMSS SATCON: 83 KTS AT 170700Z
   CIMSS ADT: 82 KTS AT 170730Z
   CIMSS DPRINT: 83 KTS AT 170600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 19P (MEGAN) IS FORECAST TO TRACK
SOUTH-SOUTHWESTWARD (TAU 00 TO TAU 12) TO SOUTHWESTWARD (TAU 12 TO
36) FOLLOWING THE STEERING INFLUENCE OF A WEAK NER TO THE EAST.
PRIOR TO LANDFALL NEAR TAU 24, A FAVORABLE ENVIRONMENT HAVING LOW
(10-15KTS) VERTICAL WIND SHEAR (VWS), VERY WARM (30-31C) SEA SURFACE 
TEMPERATURES (SST), AND IMPROVING OUTFLOW ALOFT (COLLOCATED WITH 
UPPER-LEVEL POINT SOURCE) LEAVES ROOM FOR FURTHER INTENSIFICATION TO 
OCCUR THROUGH TAU 12. ONCE INTERACTION WITH LAND AND FRICTIONAL 
COMPONENTS BEGIN TO IMPACT THE STORM, A RAPID WEAKENING TREND IS 
ANTICIPATED TO START NEAR TAU 12 AND CONTINUE THROUGH TAU 72 AS THE 
SYSTEM TRACKS INLAND. SHORTLY AFTER TAU 36 THE PRIMARY STEERING 
INFLUENCE IS EXPECTED TO SHIFT FROM THE PREVIOUSLY MENTIONED NER TO A 
STR OVER CENTRAL AUSTRALIA AND STEER THE SYSTEM WESTWARD THROUGH TAU 
72. DISSIPATION IS FORECAST TO BE COMPLETE BY TAU 72 OVER NORTHERN 
AUSTRALIA.

MODEL DISCUSSION: GLOBAL NUMERICAL MODEL GUIDANCE IS IN OVERALL
GOOD AGREEMENT OVER THE DURATION OF THE FORECAST INTERVAL, WITH THE
MOST SIGNIFICANT UNCERTAINTY BEING TRACK SPEED BETWEEN TAU 00 AND
TAU 36. THE CROSS-TRACK SPREAD AMONG JTWC CONSENSUS MEMBERS IS 56NM
BETWEEN ECMWF ENSEMBLE MEAN (WESTERN-MOST) AND GALWEM (EASTERN-MOST) 
BY TAU 36, WITH A HIGHER ALONG TRACK SPREAD OF 102NM BETWEEN GFS 
(SOUTHERN-MOST) AND GALWEM (NORTHERN-MOST) OVER THE SAME INTERVAL. 
THE CROSS TRACK SPREAD MORE THAN DOUBLES TO 135NM BY TAU 72. THE 
INTENSITY FORECAST, LIKELY DUE TO A SLIGHTLY HIGHER THAN ANTICIPATED 
TRACK SPEED OVER THE PAST 12 HOURS, HAS SHIFTED PEAK INTENSITY TO 
OCCUR EARLIER IN TIME (TAU 12) THAN PREVIOUSLY FORECAST. STATISTICAL-
DYNAMICAL GUIDANCE OVERSHOOTS THE JTWC INTENSITY FORECAST, WHILE 
MESOSCALE AND GLOBAL MODEL SOLUTIONS COME IN JUST UNDER THE FORECAST. 
THE OVERALL GOOD AGREEMENT WITH SOME UNCERTAINTY PRESENTED 
CONTRIBUTES TO THE OVERALL FORECAST CONFIDENCE OF MEDIUM.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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