WDPS31 PGTW 190900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 31P (THIRTYONE) WARNING 
NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.7S 141.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 597 NM EAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 31P WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) AND DEEP CONVECTION FLARING ALONG THE SOUTHERN SEMICIRCLE. A
190430Z AMSR2 89 GHZ MICROWAVE IMAGE REVEALED THE WELL-DEFINED
LOW-LEVEL CLOUDS BANDS WRAPPING INTO THE CENTER. 31P APPEARS TO HAVE
STARTED ITS WESTWARD TURN, EVIDENT BY THE SOUTHWESTWARD JOG OVER
THE PAST 6 HOURS OR SO. THE CURRENT POSITION IS ANALYZED TO BE
ABOUT 48 NM DUE WEST OF WEIPA, AUSTRALIA. ENVIRONMENTAL ANALYSIS
INDICATES THAT 31P IS IN A MARGINAL ENVIRONMENT CHARACTERIZED BY
WEAK POLEWARD OUTFLOW ALOFT, MODERATE (15-20 KTS) NORTHEASTERLY
VERTICAL WIND SHEAR, SLIGHT DRY AIR ENTRAINMENT, AND WARM (29-30 C)
SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC IN ANIMATED MSI. THE
INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON PERSISTENCE FROM EARLIER ASCAT DATA, AGENCY DVORAK CI
ESTIMATES OF 1.5-2.0, AND THE OBJECTIVE INTENSITY ESTIMATES RANGING
FROM 26-36 KTS.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   DEMS: T2.0 - 30 KTS
   CIMSS SATCON: 36 KTS AT 190540Z
   CIMSS ADT: 34 KTS AT 190600Z
   CIMSS AIDT: 30 KTS AT 190600Z
   CIMSS DPRINT: 27 KTS AT 190600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: SLIGHT DRY AIR ENTRAINMENT ALONG THE NORTHERN
PORTION OF THE SYSTEM

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 31P IS FORECAST TO TRACK WEST-SOUTHWESTWARD
OVER THE NEXT 12 HOURS BEFORE THE STR BUILDS IN TO THE SOUTH OF THE
VORTEX AND BEGINS PROPAGATING WESTWARD. NEAR TAU 24, THE SYSTEM IS
FORECAST TO START ON A WEST-NORTHWESTWARD TRACK AS THE SYSTEM RIDES
ALONG THE NORTHERN PERIPHERY OF THE STR THROUGH THE REMAINDER OF
THE FORECAST PERIOD. REGARDING INTENSITY, 31P IS FORECAST TO BEGIN
SLIGHTLY INTENSIFYING WITHIN THE GULF OF CARPENTARIA AS THE VORTEX
BECOMES BETTER ALIGNED THROUGH THE MID-LEVELS AND THE ENVIRONMENT
MOISTENS. A PEAK OF AROUND 40 KTS IS FORECAST TO OCCUR BETWEEN TAU
36 AND 48, BEFORE THE SYSTEM BEGINS TO SKIRT ALONG THE NORTHERN TOP
END. AFTER TAU 48, 31P IS FORECAST TO REMAIN RIGHT AROUND 35 KTS
THROUGH TAU 96 DUE TO LAND INTERACTION AND AN OVERALL MARGINAL
ENVIRONMENT. AFTER TAU 96, UPPER-LEVEL SHEAR IS EXPECTED TO
INCREASE TO NEAR 25 KTS, CAUSING THE VORTEX TO FURTHER SHALLOW AND
EVENTUALLY DISSIPATE NEAR TAU 120. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN MODERATE
AGREEMENT THROUGH TAU 72 WITH A 130 NM CROSS-TRACK SPREAD AT TAU
72. NAVGEM MAKES UP FOR THE MAJORITY OF THE SPREAD THOUGH,
TRACKING THE VORTEX FURTHER SOUTHWARD THAN THE REMAINDER OF
GUIDANCE. AFTER TAU 72, ALONG-TRACK SPREAD INCREASES SIGNIFICANTLY
WITH ECMWF AND GFS ACCELERATING THE VORTEX NORTHWESTWARD WHILE
GALWEM, UKMET, AND NAVGEM DEPICT SLOWER TRACK SPEEDS. THE JTWC
TRACK FORECAST IS PLACED SLIGHTLY CLOSER TO THE GFS AND ECMWF
MODELS WITH MEDIUM CONFIDENCE THROUGH TAU 72 AND LOW CONFIDENCE
THEREAFTER. INTENSITY GUIDANCE AGREES ON MARGINAL INTENSIFICATION
THROUGH TAU 42 AND THEN A STEADY INTENSITY THROUGH TAU 96 AND
WEAKENING THROUGH TAU 120. NOTABLY, GFS KEEPS THE SYSTEM WEAKER
THAN MESOSCALE MODELS DO, BUT ALSO HAS THE VORTEX TRACK CLOSER TO
THE TOP END THAN HAFS-A, HWRF, AND COAMPS-TC DOES. OVERALL, THE
JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE. THE
AMOUNT OF LAND INTERACTION WILL PLAY A BIG ROLE IN HOW MUCH THE
SYSTEM IS ABLE TO DEVELOP.

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