WDXS31 PGTW 060900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12S (JENNA) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.7S 94.8E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 243 NM SOUTH-SOUTHWEST OF THE COCOS
ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 12S (JENNA) IS ANALYZED TO HAVE RAPIDLY
INTENSIFIED OVER THE PAST 24 HOURS, FROM 45 KTS TO 90 KTS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TC 12S WITH A 10 NM
PARTIALLY CLOUD FILLED EYE AND A DEFINED RING OF COLD CLOUD TOPS
SURROUNDING THE EYEWALL. A 060711Z AMSR2 89 GHZ MICROWAVE IMAGE
REVEALED WELL-DEFINED TIGHTLY CURVED CONVECTIVE BANDING WITH A
SLIGHT WEAKNESS IN THE NORTHERN PORTION OF THE EYEWALL. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE IN
ANIMATED MSI. THE INITIAL INTENSITY OF 90 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS
OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS
INDICATES THAT 12S IS IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY
STRONG POLEWARD OUTFLOW ALOFT, LOW (10-15 KTS) NORTHERLY VERTICAL
WIND SHEAR, AND WARM (27-28 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: 060328Z METOP-C ASCAT SCATTEROMETER DATA

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) CENTERED OVER WESTERN AUSTRALIA. 


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   DEMS: T4.5 - 77 KTS
   APRF: T4.5 - 77 KTS
   CIMSS ADT: 102 KTS AT 060600Z
   CIMSS AIDT: 95 KTS AT 060600Z
   CIMSS D-MINT: 100 KTS AT 060711Z
   CIMSS D-PRINT: 96 KTS AT 060600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE RAPID DEVELOPMENT OF THE SYSTEM
CAUSED NEAR-TERM INTENSITIES TO BE HIGHER THAN PREVIOUSLY FORECAST.
OTHERWISE, THERE ARE NO SIGNIFICANT CHANGES.

FORECAST DISCUSSION: TC 12S IS FORECAST TO CONTINUE TRACKING
SOUTHWESTWARD, ALONG THE NORTHWESTERN PERIPHERY OF THE STR THROUGH
TAU 24. NEAR TAU 24, THE SYSTEM IS EXPECTED TO MAKE A WESTWARD TURN
AS THE STEERING MECHANISM SWITCHES TO A LOW TO MID-LEVEL STR
CENTERED TO THE SOUTHWEST. A WESTWARD TRACK, ALONG THE NORTHERN
PERIPHERY OF THE STR, IS FORECAST TO PERSIST THROUGH THE REMAINDER
OF THE FORECAST PERIOD. REGARDING INTENSITY, 12S IS FORECAST TO
MAINTAIN INTENSITY OR BEGIN SLIGHTLY WEAKENING OVER THE NEXT 12
HOURS. AFTER TAU 12, NORTHWESTERLY SHEAR IS EXPECTED TO INCREASE TO
AROUND 20 KTS. IN ADDITION TO THE SHEAR, SIGNIFICANT DRY AIR
ENTRAINMENT FROM THE NORTH WILL FURTHER AID IN WEAKENING THE
SYSTEM. AS A RESULT, 12S IS FORECAST TO RAPIDLY WEAKEN THROUGH TAU
48 TO AROUND 40 KTS. THE SYSTEM IS FORECAST TO WEAKEN BELOW 35 KTS
NEAR TAU 72 AS THE SHALLOW VORTEX CONTINUES TO TRACK OFF TO THE WEST.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGHOUT THE FORECAST PERIOD WITH NO SIGNIFICANT
OUTLIERS. CROSS-TRACK AND ALONG-TRACK SPREAD AT TAU 72 IS AROUND 80
NM AND 140 NM RESPECTIVELY. THE JTWC TRACK FORECAST IS PLACED CLOSE
TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE. INTENSITY
GUIDANCE GENERALLY AGREES ON SLIGHT WEAKENING THROUGH TAU 12 AND
RAPID WEAKENING THEREAFTER. THE JTWC INTENSITY FORECAST IS ALSO
PLACED NEAR THE MULTI-MODEL CONSENSUS, BUT WITH MEDIUM CONFIDENCE
DUE TO SOME UNCERTAINTIES CONCERNING THE INTENSITY OVER THE NEXT
12-24 HOURS.

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