WDPS31 PGTW 062100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 30P (MAILA) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.9S 156.1E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 665 NM SOUTH OF KAPINGAMARANGI
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A RAGGED
INNER CORE STRUCTURE, WITH AN EMBEDDED CENTER OR EYE DIMPLE
PERIODICALLY VISIBLE WITHIN AN ASYMMETRIC DISC OF DEEP CONVECTION.
THE CORE IS EXHIBITING SIGNS OF PROBABLE OCEANIC UPWELLING BENEATH
THE SLOW-MOVING STORM, WITH A 061519Z AMSR-2 MICROWAVE PASS SHOWING
ONLY HALF AN EYEWALL PRESENT, WITH THE EASTERN SEMICIRCLE DEVOID OF
DEEP CONVECTIVE BANDING AT THE TIME. COUPLED TROPICAL CYCLONE
MODELS HAFS-A AND HWRF ASSESS THAT A POOL OF WATER COOLER THAN 26
DEGREES CELSIUS HAS DEVELOPED NEAR AND JUST NORTH OF THE STORM
TRACK. THERE IS ALSO LIGHT EASTERLY SHEAR OF 10-15 KT PRESENT,
CONTRIBUTING TO LESS EXPANSIVE CONVECTIVE BANDING IN THE EASTERN
SEMICIRCLE. THE INITIAL INTENSITY IS LOWERED TO 90 KT BASED ON THE
DEGRADING STRUCTURE AND A SPREAD OF AGENCY DVORAK ESTIMATES AND
OBJECTIVE SATELLITE-BASED INTENSITY ESTIMATES, RANGING RATHER
WIDELY FROM ABOUT 65 KT TO 100 KT.

INITIAL WIND RADII BASIS: AMSR-2 DATA

CURRENT STEERING MECHANISM: EQUATORIAL WESTERLY WIND BURST AND
SUBTROPICAL RIDGE OVER AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   KNES: T6.0 - 115 KTS
   ABRF: T5.5 - 102 KTS
   CIMSS SATCON: 86 KTS AT 061516Z
   CIMSS ADT: 65 KTS AT 061730Z
   CIMSS AIDT: 70 KTS AT 061730Z
   CIMSS D-MINT: 88 KTS AT 061803Z
   CIMSS D-PRINT: 87 KTS AT 061830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 24-28 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: PROBABLE UPWELLING OF COOL WATER NEAR THE VORTEX

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE 30P (MAILA) IS TRICKY TO
FORECAST ACROSS MULTIPLE DIMENSIONS, AND TRACK AND INTENSITY ARE
CLOSELY RELATED. THE CYCLONE REMAINS MIRED BETWEEN AN EQUATORIAL
WESTERLY WIND BURST TO THE NORTH AND A SUBTROPICAL RIDGE TO THE
SOUTHWEST OVER AUSTRALIA. THE COMPETING STEERING INFLUENCES OF
THESE FEATURES IS CAUSING MAILA TO MEANDER SLOWLY, WHICH IS
CREATING OCEANIC UPWELLING AND IMPACTING THE INTENSITY FORECAST.
COUPLED MODELS HAFS-A AND HWRF SUGGEST THAT MAILA WILL REMAIN NEAR
ITS OWN COLD WAKE AS IT EVENTUALLY TURNS BACK WESTWARD OVER THE
NEXT 36 TO 48 HOURS. THIS IS ANTICIPATED TO CAUSE SOME FURTHER
WEAKENING SHORT-TERM, BUT WITHOUT DIRECT OCEAN OBSERVATIONS TO MAP
OUT THE COLD WAKE BENEATH THE STORM, THERE IS CONSIDERABLE
UNCERTAINTY IN THE SHORT-TERM INTENSITY TREND. A WESTWARD TRACK
MOTION IS EXPECTED TO DEVELOP AS THE SUBTROPICAL RIDGE OVER
AUSTRALIA BUILDS SLIGHTLY EASTWARD, BUT MODELS DISAGREE
SUBSTANTIALLY ON TIMING OF THE ONSET OF THIS MOTION. THE UKMET AND
AI-BASED MODELS ARE MUCH SLOWER THAN THE ECMWF, GFS, AND HAFS-A.
THIS COMPOUNDS INTO HIGHER THAN AVERAGE ALONG-TRACK SPREAD OVER THE
ENTIRE FORECAST. THE JTWC TRACK FORECAST CURRENTLY SITS BETWEEN THE
FAST AND SLOW GROUPS, TAKING 30P NEAR THE TIP OF THE PAPUAN
PENINSULA BETWEEN 72 AND 96 HOURS. THIS WILL BE ANOTHER PIVOT POINT
IN THE STORM'S LIFECYCLE AS IT TRACKS OVER OR NEAR THE ABRUPT
TERRAIN OF THE OWEN STANLEY MOUNTAIN RANGE. EVEN AN OFFSHORE TRACK
NEAR THESE MOUNTAINS WOULD LIKELY SEVERELY DISRUPT THE STORM'S
INNER CORE, BUT MODELS DISAGREE ON THE DEGREE OF DISRUPTION. SOME
MODELS LIKE THE GFS AND HAFS-A DEPICT NEAR-TOTAL COLLAPSE OF 30P
DOWNSTREAM OF THE PAPUAN PENINSULA, WHILE OTHERS LIKE ECMWF SHOW A
MODERATE STEP DOWN IN INTENSITY. AN INCREASE OF EASTERLY VERTICAL
SHEAR IN SOME MODELS ALSO CONTRIBUTES TO THE WEAKENING TREND. THE
JTWC FORECAST SHOWS ABRUPT WEAKENING TO 65 KT BETWEEN 72 AND 96
HOURS, BUT CONFIDENCE IS LOWER THAN AVERAGE GIVEN THE SENSITIVITY
TO THE PRECISE TRACK RELATIVE TO THE TERRAIN. REGARDLESS, MOST
MODELS AGREE THAT MAILA WILL CONTINUE TRACKING WEST-SOUTHWESTWARD
TOWARDS NORTHEASTERN AUSTRALIA THROUGH 120 HOURS.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS PLACED NEAR THE
MULTI-MODEL CONSENSUS BETWEEN TWO GROUPINGS OF FAST AND SLOW MODEL
PROJECTIONS. THE JTWC INTENSITY FORECAST LEANS STRONGLY TOWARD THE
COUPLED MODELS HAFS-A AND HWRF SHORT-TERM DUE TO THEIR AWARENESS OF
OCEANIC UPWELLING OCCURRING BENEATH THE VORTEX, THEN CLOSE TO THE
BROADER MULTI-MODEL CONSENSUS AFTER 48 HOURS.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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