WDPS31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19P (MEGAN)
WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.9S 137.3E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 400 NM EAST-SOUTHEAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 29 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 19P (MEGAN) EXHIBITING TROCHOIDAL MOTION AS THE SYSTEM
TRACKED GENERALLY EAST-NORTHEASTWARD OVER THE PAST SIX HOURS,
BACKTRACKING OVER PREVIOUSLY TRAVELED WATERS. A 170844Z SSMIS 37GHZ 
SATELLITE MICROWAVE IMAGE CAPTURED A WELL-DEFINED MICROWAVE EYE,
WITH THE CORRESPONDING 89GHZ IMAGE SUGGESTING THE TC VORTEX IS WELL
ALIGNED VERTICALLY. A RCM-3 SYNTHETIC APERTURE RADAR (SAR) IMAGE
OF 170919Z REPORTED UP TO 123KTS IN THE NORTHWEST QUADRANT OF THE
SYSTEM AND AS LOW AS 92KTS IN THE SOUTHWEST QUADRANT. HOWEVER, A 45
DEGREE INCIDENCE ANGLE TO THE COLLECTING SENSOR MAY HAVE POSITIVELY
SKEWED REPORTED VALUES. THE INITIAL POSITION AND INTENSITY OF 95
KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED
SAR IMAGE AND THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES
LISTED BELOW.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: WEAK NER EXTENSION TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T5.0 - 90 KTS
   CIMSS ADT: 82 KTS AT 171200Z
   CIMSS AIDT: 78 KTS AT 171200Z
   CIMSS DPRINT: 78 KTS AT 171200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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
NORTHEAST. PRIOR TO LANDFALL NEAR TAU 24, A FAVORABLE ENVIRONMENT
HAVING LOW TO MODERATE (10-20KTS) VERTICAL WIND SHEAR (VWS), VERY 
WARM (30-31C) SEA SURFACE TEMPERATURES (SST), AND MODERATE POLEWARD 
OUTFLOW ALOFT (COLLOCATED WITH UPPER-LEVEL POINT SOURCE) LEAVES ROOM 
FOR FURTHER INTENSIFICATION TO OCCUR THROUGH TAU 06. ONCE INTERACTION 
WITH LAND AND FRICTIONAL COMPONENTS BEGIN TO IMPACT THE STORM, A 
RAPID WEAKENING TREND IS ANTICIPATED TO START AT OR PRIOR TO TAU 06 
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. DISREGARDING NAVGEM TRACKING WESTWARD FROM TAU 00 TO TAU
72, THE CROSS-TRACK SPREAD AMONG JTWC CONSENSUS MEMBERS IS 71NM BY
TAU 36, WITH A HIGHER ALONG TRACK SPREAD OF 93NM OVER THE SAME
INTERVAL. BY TAU 72, THE CROSS-TRACK SPREAD BETWEEN ALL JTWC
CONSENSUS MEMBERS IS 109NM. OVERALL, INTENSITY GUIDANCE SUGGESTS TC
19P HAS OR WILL REACH PEAK INTENSITY BY TAU 06 WITH A DOWNTREND
AND WEAKENING THEREAFTER TO TAU 72. STATISTICAL-DYNAMICAL GUIDANCE
(SHIPS) IS THE ONLY OUTLIER AMONG INTENSITY CONSENSUS MEMBERS, AND 
SOLELY SUGGESTS A CONTINUED INTENSIFICATION PERIOD THROUGH TAU 12,
FOLLOWED BY A DOWNTREND TO TAU 72. 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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