WDXS32 PGTW 290900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12S (ELVIS) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.0S 42.6E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 214 NM SOUTHEAST OF EUROPA ISLAND
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 12S (ELVIS) WITH A WELL-DEFINED, EXPOSED LOW-LEVEL
CIRCULATION CENTER AND CONVECTION TRAILING OFF TO THE SOUTH. 12S
HAS EXHIBITED MORE TROPICAL CHARACTERISTICS OVER THE PAST 6 HOURS,
PARTICULARLY REGARDING THE SYMMETRY OF THE WIND FIELD. 290534Z
ASCAT-B IMAGE REVEALS THAT THE LLCC HAS TIGHTENED UP AND SHOWS 40
KNOT WINDS WITHIN 30 NM OF THE ASSESSED CENTER. ENVIRONMENTAL
ANALYSIS INDICATES THAT 12S IS IN A MARGINAL ENVIRONMENT
CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT AND WARM (28-29 C)
SEA SURFACE TEMPERATURES OFFSET BY MODERATE TO HIGH (20-25 KTS)
VERTICAL WIND SHEAR AND DRY AIR WITHIN THE WESTERN SECTOR OF THE
SYSTEM. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED
ON THE EXPOSED LLCC IN ANIMATED MSI. THE INITIAL INTENSITY OF 40
KTS IS ALSO ASSESSED WITH HIGH CONFIDENCE BASED ON THE MENTIONED
ASCAT-B IMAGE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: PLACED WITHIN A COMPETING STEERING
ENVIRONMENT, WITH A SUBTROPICAL RIDGE (STR) TO BOTH THE EAST AND
WEST OF THE SYSTEM. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   FMEE: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR WITHIN THE WESTERN SECTOR OF THE SYSTEM

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: 12S IS FORECAST TO STAY QUASI-STATIONARY (QS)
OVER THE NEXT 12 HOURS AS IT REMAINS PLACED WITHIN THE COMPETING
STEERING ENVIRONMENT. AFTER TAU 12, THE RIDGE TO THE EAST WILL
BEGIN TO TAKE OVER AS THE PRIMARY STEERING MECHANISM, DRIVING THE
SYSTEM SOUTHEASTWARD. HOWEVER, THERE IS SOME DISCREPANCY BETWEEN
THE QS TIMELINE BETWEEN MODELS AND THERE IS A POSSIBILITY THAT THE
VORTEX REMAINS QS LONGER. REGARDING INTENSITY, 12S IS FORECAST TO 
MAINTAIN INTENSITY OVER THE NEXT 36 HOURS DUE TO THE
FAVORABLE SEA SURFACE TEMPERATURES (SST) AND STRONG POLEWARD
OUTFLOW FIGHTING THE SHEAR AND DRY AIR. AFTER TAU 36, THE SHEAR
BEGINS TO RISE TO AROUND 30 KTS AND SST DROP BELOW 26 C, CAUSING
WEAKENING. AT THE SAME TIME, 12S IS FORECAST TO BEGIN TRANSITIONING
INTO A SUBTROPICAL CYCLONE AS IT BEGINS TO INTERACT WITH A BRANCH
OF THE UPPER-LEVEL JET. COMPLETION OF SUBTROPICAL TRANSITION IS
EXPECTED AROUND TAU 48.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN POOR AGREEMENT ON
THE TRACK OF 12S, WITH MODELS DISPLAYING VARYING AMOUNTS OF TIME AS 
QS. GFS AND ITS ENSEMBLE MEAN KEEP THE VORTEX QS THE LONGEST, WITH
EVEN A SLIGHT JOG NORTHWARD THROUGH TAU 24, BEFORE TRACKING
SOUTHEASTWARD. ECMWF BEGINS THE SOUTHEASTWARD TRACK SOONER AND THE
REMAINDER OF GUIDANCE FOLLOWS MORE CLOSELY TO THIS SCENARIO. AS A
RESULT, THE JTWC TRACK FORECAST IS PLACED CLOSER TO ECMWF WITH LOW
CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN POOR AGREEMENT, WITH GFS,
HAFS-A, AND HWRF SUGGESTING A GRADUAL WEAKENING TREND WHILE ECMWF
HAS THE VORTEX MAINTAINING INTENSITY FOR LONGER. THE JTWC INTENSITY
FORECAST FOLLOWS CLOSER TO THE ECMWF SOLUTION DUE TO THE
ENVIRONMENT NOT BECOMING OVERLY UNFAVORABLE WITHIN THE NEXT 48
HOURS.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   INTENSITY 0 - 72 HR: LOW//
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