WDXS31 PGTW 070900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12S (JENNA) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.0S 92.2E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 442 NM SOUTHWEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 12S (JENNA) WITH DEEP CONVECTION DRIFTING OFF TO THE SOUTH
OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE SEPARATION OF THE
CONVECTION FROM THE CENTER OF THE SYSTEM HAS CAUSED THE NORTHERN
PORTION OF THE LLCC TO BECOME INCREASINGLY EXPOSED OVER THE PAST 6
HOURS. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED
ON CLOUD TRACING IN THE ANIMATED MSI. THE INITIAL INTENSITY OF 60
KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF THE
AGENCY DVORAK FIXES AND CIMSS OBJECTIVE INTENSITY ESTIMATES LISTED
BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 12S IS NOW IN AN
UNFAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW
HEAVILY OFFSET BY MODERATE VERTICAL WIND SHEAR, SIGNIFICANT DRY AIR
ENTRAINMENT, AND MARGINAL (26-27 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: PERSISTENCE FROM THE 062309Z RCM-3 SAR
IMAGE WITH SLIGHT ADJUSTMENTS BASED ON THE OBJECTIVE BEST TRACK

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   DEMS: T4.0 - 65 KTS
   APRF: T4.0 - 65 KTS
   CIMSS SATCON: 54 KTS AT 070710Z
   CIMSS ADT: 65 KTS AT 070610Z
   CIMSS AIDT: 60 KTS AT 070610Z
   CIMSS D-PRINT: 46 KTS AT 070610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT FROM THE WEST AND
NORTH

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 12S IS FORECAST TO TRACK SOUTHWESTWARD FOR
ONLY ANOTHER 12 HOURS OR SO BEFORE MAKING A WESTWARD TURN AS THE
STEERING MECHANISM SWITCHES TO A LOW TO MID-LEVEL RIDGE POSITIONED
TO THE SOUTHWEST. 12S IS THEN FORECAST TO TRACK GENERALLY WESTWARD,
ALONG THE NORTHERN PERIPHERY OF THE RIDGE THROUGH THE REMAINDER OF
THE FORECAST PERIOD. THE ENVIRONMENT IS EXPECTED TO ONLY WORSEN
WITH INCREASING NORTHWESTERLY VERTICAL WIND SHEAR DRY AIR
ENTRAINMENT, CAUSING 12S TO WEAKEN THROUGHOUT THE FORECAST PERIOD.
THE VORTEX IS EXPECTED TO COMPLETELY SHALLOW OUT AND DECOUPLE
WITHIN THE NEXT 24 HOURS AS DRY AIR ENGULFS THE SYSTEM. 12S IS
FORECAST TO DISSIPATE NEAR TAU 48 AS THE SYSTEM 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 SPREAD IS AROUND 80 NM AT TAU 48 WITH GALWEM
BEING THE NORTHERNMOST MEMBER WHILE ECMWF IS THE SOUTHERNMOST
MEMBER. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL
CONSENSUS WITH HIGH CONFIDENCE. INTENSITY GUIDANCE AGREES ON
WEAKENING THROUGHOUT THE FORECAST PERIOD AND THE JTWC INTENSITY
FORECAST ALSO FOLLOWS THE CONSENSUS WITH HIGH CONFIDENCE.

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