WDPS31 PGTW 170300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19P (MEGAN) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.9S 137.4E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 405 NM EAST-SOUTHEAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE 19P (MEGAN) HAS CONTINUED TO RAPIDLY INTENSIFY
OVER THE ZESTY WATERS OF THE SOUTHERN GULF OF CARPENTARIA. AFTER
ACHIEVING A VERTICALLY ALIGNED VORTEX THIS MORNING, THE SYSTEM HAS
CONTINUED TO DEVELOP A STRONGER INNER-CORE OF DEEP CONVECTION,
THOUGH AS OF YET HAS NOT FORMED AN EYE FEATURE IN EITHER THE
VISIBLE OR INFRARED CHANNELS. THE LATEST ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) SHOWS VERY DENSE INNER-CORE CONVECTIVE
ACTIVITY, WITH OVERSHOOTING TOPS AND CLOUD TOP TEMPERATURES AS LOW
AS -94C. ADDITIONALLY, AN EXTREMILY POTENT INNER-CORE LIGHTNING BURST
IS ONGOING, WHICH IS A STRONG INDICATOR OF ADDITIONAL
INTENSIFICATION IN THE OFFING. A 161958Z SSMIS 91GHZ MICROWAVE
IMAGE REVEALED A WELL-DEFINED MICROWAVE EYE, THOUGH THE EYE IN THE
37GHZ BAND HAD A MUCH WEAKER REPRESENTATION. REGARDLESS, TRACKING
OF THE EYE FEATURE SHOWED THAT THE SYSTEM MADE A SMALL CLOCKWISE
LOOP BETWEEN 1200Z AND 2000Z AND IS NOW TRACKING TOWARDS THE
SOUTHEAST. THE INITIAL POSITION WAS ASSESSED WITH MEDIUM
CONFIDENCE, UNDER THE COLDEST CLOUD TOPS IN THE EIR WITH SUPPORT
FROM RADAR POSITIONING DATA. THE INITIAL INTENSITY WAS ASSESSED
WITH MEDIUM CONFIDENCE, ON THE HIGHER END OF THE AVAILABLE
OBJECTIVE AND SUBJECTIVE FIXES NOTED BELOW. THE ENVIRONMENT REMAINS
FAVORABLE, WITH LOW TO MODERATE EASTERLY ENVIRONMENTAL SHEAR, VERY
WARM SSTS, HIGH OHC AND MODERATE WESTWARD AND EQUATORWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   ADRM: T4.0 - 65 KTS
   CIMSS SATCON: 74 KTS AT 170000Z
   CIMSS ADT: 79 KTS AT 162330Z

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

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: TC 19P HAS COMPLETED A TIGHT CLOCKWISE LOOP
OVER THE PAST SIX HOURS, HAVE ABSCONDED BRIEFLY IN A WEAK STEERING
ENVIRONMENT. BUT NOW IT HAS PICKED UP SOME SPEED, HEADED TOWARDS THE
SOUTHWEST COAST OF THE GULF OF CARPENTARIA, ALONG THE WESTERN SIDE
OF A MID-LEVEL NER CENTERED TO THE NORTHEAST. THE NER IS EXPECTED
TO WEAKEN SOMEWHAT OVER THE NEXT 12 TO 24 HOURS, WHICH WILL LOOSEN
THE STEERING GRADIENT BY A NOTCH OR TWO, THUS ALLOWING TC 19P TO
SLOW DOWN TO 2-3 KNOTS AS IT APPROACHES THE COAST. LANDFALL IS
EXPECTED AROUND TAU 24 IN THE VICINITY OF THE SIR EDWARD PELLEW
GROUP. AFTER LANDFALL, TRACK SPEEDS WILL REMAIN LOW OR EVEN SLOW A
BIT MORE AS A WEAKNESS DEVELOPS IN THE MID-LEVEL RIDGE PATTERN.
AFTER TAU 48 THE SYSTEM WILL BEGIN TO ACCELERATE WESTWARD AS IT
COMES UNDER THE INFLUENCE OF A BUILDING SUBTROPICAL RIDGE (STR) TO
THE SOUTH. IN TERMS OF INTENSITY, THE SYSTEM HAS CONTINUED TO
RAPIDLY INTENSIFY, EVEN IN THE FACE OF MODERATE EASTERLY
ENVIRONMENTAL SHEAR. NO SIGNIFICANT CHANGES ARE EXPECTED IN THE
OVERALL ENVIRONMENT OVER THE NEXT 12 TO 18 HOURS, THUS THE SYSTEM
IS FORECAST TO CONTINUE TO INTENSIFY, UP TO A PEAK OF 95 KNOTS BY
TAU 12. THE SYSTEM WILL MAINTAIN THIS PEAK INTENSITY THROUGH
LANDFALL EVEN AFTER DEEP-LAYER ENVIRONMENTAL SHEAR ALONG WITH A
BURST OF CONVERGENT NORTHEASTERLY FLOW ALOFT, MOVES IN AROUND TAU
18. ONCE ASHORE HOWEVER, THE SYSTEM WILL QUICKLY WEAKEN AND
ULTIMATELY DISSIPATE OVER NORTH-CENTRAL AUSTRALIA BY TAU 72. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
AND HAS IMPROVED SINCE THE PREVIOUS RUN, WITH NO SIGNIFICANT OUTLIERS
AT THIS TIME. THE TRACK SPREAD HAS REDUCED TO JUST 100NM BY THE END
OF THE FORECAST PERIOD. HOWEVER, TRACK SPEED IS THE MORE DOMINANT
CONCERN AND THERE IS A SIGNIFICANT AMOUNT OF ALONG-TRACK SPREAD,
PARTICULARLY IN THE FIRST 36 HOURS OF THE FORECAST. THE JTWC
FORECAST TRACKS CLOSE TO THE CONSENSUS MEAN IN BOTH DIRECTION AND
SPEED, BUT CONFIDENCE IS ONLY MEDIUM DUE TO THE POSSIBILITY OF A
FASTER SPEED OF ADVANCE IN THE FIRST 36 HOURS OF THE FORECAST.
INTENSITY GUIDANCE REMAINS MIXED, WITH THE MESOSCALE MODELS (HWRF,
HAFS-A, AND COAMPS-TC) STUBBORNLY REFUSING TO ACKNOWLEDGE THE
POSSIBILITY OF ADDITIONAL INTENSIFICATION, AS THEY HAVE BEEN DOING
SINCE YESTERDAY. THE MESOSCALE MOELS ALL SHOW THE SYSTEM
MAINTAINING INTENSITY TO TAU 12 THEN FALLING OFF SHARPLY
THEREAFTER. MEANWHILE, THE SHIPS GUIDANCE (BOTH GFS AND NAVGEM)
SHOW AN ADDITIONAL 15-20 KNOTS OF INTENSIFICATION, PEAKING AT 100
KTS, WHILE THE FRIA, RICN, RIPA AND RI25 TO RI 35 RAPID
INTENSIFICATION AIDS CONTINUE TO TRIGGER, PEAKING THE SYSTEM NEAR
125 KNOTS BY TAU 24. IF THE SYSTEM HAD MORE TIME OVER WATER, THE RI
PEAKS MIGHT BE REALISTIC, BUT WITH REALISTICALLY NO MORE THAN 12
HOURS OF OPEN WATERS, THE JTWC FORECAST PEAKS AT 95 KNOTS.

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