WDXS31 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 17S (LUANA) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.8S 122.5E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 68 NM NORTH-NORTHEAST OF BROOME, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 17S (LUANA) CURRENTLY MAKING LANDFALL ALONG THE KIMBERLEY
COAST, SOUTHWEST OF THE DAMPIER PENINSULA. THE EXACT TIMING OF
LANDFALL IS ESTIMATED TO BE AROUND 240700Z. THE SYSTEM HAS
MAINTAINED TIGHTLY CURVED BANDS OF DEEP CONVECTION SURROUNDING THE
LOW-LEVEL CIRCULATION CENTER (LLCC). A 240520Z AMSR2 36 GHZ
MICROWAVE IMAGE REVEALED A WELL-DEFINED MICROWAVE EYE FEATURE,
ALLOWING THE INITIAL POSITION TO BE PLACED WITH HIGH CONFIDENCE.
THE INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY DVORAK FIXES AND CIMSS INTENSITY ESTIMATES
LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 17S IS
CURRENTLY IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY
STRONG RADIAL OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR,
AND WARM (29-30 C) SEA SURFACE TEMPERATURES OFFSET BY TERRAIN
INTERACTION.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: AN ELONGATED NEAR EQUATORIAL RIDGE
(NER) POSITIONED TO THE NORTH-NORTHWEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   APRF: T3.5 - 55 KTS
   CIMSS SATCON: 51 KTS AT 240300Z
   CIMSS ADT: 51 KTS AT 240220Z
   CIMSS AIDT: 43 KTS AT 240220Z
   CIMSS D-MINT: 58 KTS AT 240520Z
   CIMSS D-PRINT: 50 KTS AT 240520Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: TERRAIN INTERACTION

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 17S IS FORECAST TO TRACK SOUTHEASTWARD,
FURTHER INLAND, OVER THE NEXT 12 HOURS. NEAR TAU 12, A RIDGE IS
EXPECTED TO BUILD OVER CENTRAL AUSTRALIA, CAUSING 17S TO TURN MORE
SOUTHWARD AS IT RIDES ALONG THE WESTERN PERIPHERY OF THE RIDGE.
REGARDING INTENSITY, 17S IS FORECAST TO STEADILY WEAKEN OVER THE
NEXT 24 HOURS AS TERRAIN INTERACTION ERODES THE VORTEX. WEAKENING
BELOW TC STRENGTH IS FORECAST TO OCCUR NEAR TAU 36, AS THE SYSTEM
TRACKS FURTHER INLAND WITHIN WESTERN AUSTRALIA. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH NO SIGNIFICANT OUTLIERS. CROSS-TRACK SPREAD AT TAU
36 IS AROUND 90 NM. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE
MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS
ALSO IN GOOD AGREEMENT, WITH ALL MODELS SHOWING STEADY WEAKENING
THROUGH TAU 36. AS A RESULT, THE JTWC INTENSITY FORECAST IS ALSO
PLACED WITH HIGH CONFIDENCE, CLOSE TO THE CONSENSUS.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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