WDXS31 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 039//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.4S 114.2E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 186 NM SOUTH OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
RAPIDLY DECAYING CYCLONE WITH COLLAPSING CONVECTION DISPLACED TO
THE EAST OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE ANIMATED
EIR CONTINUES TO SHOW STABLE STRATIFORM CLOUDS BEING ENTRAINED FROM
THE WEST INTO THE CORE OF THE VORTEX. A 271048Z WSFM 89 GHZ
MICROWAVE IMAGE CONFIRMED THE ASYMMETRIC NATURE OF THE CONVECTION
WITH EXPOSED CLOUD LINES ON THE WESTERN PORTION OF THE SYSTEM
WRAPPING INTO THE CENTER. THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON ANIMATED RADAR IMAGERY FROM THE
CARNARVON RADAR SITE SHOWING AN INCREASINGLY RAGGED LLCC, PASSING
JUST EAST OF SHARK BAY. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED
WITH LOW CONFIDENCE BASED ON THE RAPIDLY DECAYING STRUCTURE AND A
LACK OF WIND OBSERVATIONS IN THE IMMEDIATE VICINITY. THE CURRENT
ENVIRONMENT IS CHARACTERIZED AS HIGHLY UNFAVORABLE DUE TO HIGH
VERTICAL WIND SHEAR (VWS), DRY AIR ENTRAINMENT FROM THE WEST, AND
TERRAIN INTERACTION.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
ANTICYCLONE OVER WEST-CENTRAL AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   CIMSS D-MINT: 77 KTS AT 271006Z
   CIMSS D-PRINT: 75 KTS AT 271120Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 25-30 KTS
   SST: OVER LAND
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: TERRAIN INTERACTION AND DRY AIR ENTRAINMENT FROM
THE WEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: LOW
   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 27P (NARELLE) IS ACCELERATING TOWARD THE
SOUTH-SOUTHEAST WITH INCREASING INFLUENCE OF THE MID-LATITUDE
WESTERLIES AS IT TRANSITS ACROSS WESTERN AUSTRALIA. THE SYSTEM IS
FORECAST TO TRACK ABOUT 70 NM EAST OF GERALDTON AROUND 272000Z
BEFORE EJECTING OFF THE SOUTHERN COAST OF WESTERN AUSTRALIA BY TAU
24. LAND INTERACTION, INCREASING WESTERLY VWS (UP TO 35-40 KTS BY
TAU 12), AND FURTHER DRY AIR ENTRAINMENT FROM THE WEST WILL RESULT
IN CONTINUED RAPID WEAKENING. AN INTENSITY OF 45 KTS IS FORECAST AT
TAU 12 WITH FURTHER WEAKENING TO 35 KTS AT TAU 24 WITH GALE-FORCE
WINDS PRIMARILY CONFINED TO THE EASTERN SEMICIRCLE. TC NARELLE WILL
IMMINENTLY BEGIN SUBTROPICAL TRANSITION, BECOMING FULLY SUBTROPICAL
NO LATER THAN TAU 24.

MODEL DISCUSSION: THE TRACK GUIDANCE IS IN GOOD AGREEMENT ON A
SOUTH-SOUTHEASTWARD MOTION THROUGH THE ENTIRE FORECAST PERIOD WITH
A CROSS-TRACK SPREAD OF 45 NM AT TAU 24. THE MULTI-MODEL CONSENSUS
WAS USED TO SET THE JTWC FORECAST TRACK AND IS PLACED WITH HIGH
CONFIDENCE. RAPID WEAKENING IS INDICATED BY THE ENTIRE INTENSITY
MODEL GUIDANCE SUITE. THE JTWC INTENSITY FORECAST IS PLACED
SLIGHTLY LOWER THAN THE MULTI-MODEL CONSENSUS WITH MEDIUM
CONFIDENCE BASED ON THE OBSERVED RAPID DECAY AND GIVEN THE
UNCERTAINTY ASSOCIATED WITH RATE OF WEAKENING OVER LAND.

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