WDXS31 PGTW 050900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12S (JENNA) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.2S 97.1E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 12 NM EAST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SLOW
IMPROVING TREND FOR TROPICAL CYCLONE (TC) 12S (JENNA). CONVECTION
PERSISTS AROUND THE CIRCULATION CENTER WITH VISIBLE WRAPPING
FEATURES INDICATING SLIGHT STRENGTHENING OVER THE PAST SIX HOURS.
CLOUD TOP TEMPERATURES CONTINUE TO COOL AS SEEN ON ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY. ENVIRONMENTAL ANALYSIS
REVEALS MARGINALLY FAVORABLE CONDITIONS WITH WARM (28-29 C) SEA
SURFACE TEMPERATURES (SST), LOWE (5-10 KTS) VERTICAL WIND SHEAR
(VWS) AND MODERATE POLEWARD OUTFLOW. THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON SATELLITE FIXES FROM PGTW AND APRF.
THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE OBJECTIVE AND SUBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: BUILDING SUBTROPICAL RIDGE TO THE
SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   APRF: T3.0 - 45 KTS
   CIMSS SATCON: 50 KTS AT 050700Z
   CIMSS ADT: 45 KTS AT 050700Z
   CIMSS AIDT: 34 KTS AT 050700Z
   CIMSS D-MINT: 39 KTS AT 050648Z
   CIMSS D-PRINT: 47 KTS AT 050700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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 JENNA WILL NOW TRACK SOUTH-SOUTHWESTWARD
UNDER THE INFLUENCE OF A BUILDING SUBTROPICAL RIDGE CENTERED TO THE
SOUTHEAST. THE SYSTEM WILL CONTINUE TO SLOWLY STRENGTHEN UNTIL
AFTER TAU 24 WHEN A FORECASTED INCREASE IN VERTICAL WIND SHEAR
ALONG WITH PROLONGED EXPOSURE TO DRIER AIR FROM THE SURROUNDING
ENVIRONMENT WILL CAUSE TC JENNA TO STEADILY WEAKEN. THIS WEAKENING
TREND WILL CONTINUE CULMINATING IN THE DISSIPATION OF TC JENNA AS A
TROPICAL STORM AROUND TAU 96, DRIVEN BY DRY AIR ENTRAINMENT AND
DRASTICALLY INCREASING VWS ASSOCIATED WITH AN UPPER-LEVEL RIDGE.

MODEL DISCUSSION: CROSS TRACK SPREAD AMONGST MODEL GUIDANCE IS UP
TO 80 NM AT TAU 48. THE INCREASED SPREAD AFTER TAU 48 IS CAUSED BY
ONLY A FEW INTERPOLATIONS PUSHING THE SYSTEM FURTHER SOUTH THAN THE
MAJORITY. THE JTWC FORECASTED TRACK IS PLACED CLOSE TO THE MULTI
MOEL CONSENSUS WITH HIGH CONFIDENCE. SPREAD AMONGST INTENSITY
GUIDANCE IS ONLY 10 KTS, THOUGH ALL MODELS HAVE DEPICTED A SLIGHT
INCREASE IN MAX WIND SPEEDS OVER THE PAST COUPLE RUNS, WHICH
INCREASES UNCERTAINTY ASSOCIATED WITH THE LONG TERMS FORECAST. AS
SUCH THE JTWC FORECASTED INTENSITY IS PLACED WITH MEDIUM CONFIDENCE
AFTER TAU 72. 

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