WDIO31 PGTW 302100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (FENGAL) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.2N 80.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 53 NM SOUTH OF CHENNAI, INDIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED SHORTWAVE INFRARED (SWIR) SATELLITE IMAGERY DEPICTS A FULLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) LOCATED JUST OFF THE
COAST OF SOUTHEASTERN INDIA. DURING THE OVERNIGHT HOURS, THE
CONVECTIVE MASS PREVIOUSLY ASSOCIATED WITH THE LLCC PERSISTED BUT
MOVED INLAND. IN THE LAST HOUR HOWEVER, A BURST OF CONVECTION HAS
DEVELOPED TO THE SOUTHWEST OF THE CENTER AND MOVED OFFSHORE,
FORMING INTO A ROUGHLY EAST-WEST ORIENTED BAND. THIS IS CONFIRMED
BOTH BY RADAR AND IN A 301700Z GMI 37GHZ MICROWAVE IMAGE, WHICH
SHOWED A WELL-DEFINED BAND OF CONVECTION TO THE SOUTH OF A DEFINED
LLCC. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE DATA OUTLINED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH
MEDIUM CONFIDENCE BY AVERAGING THE OBJECTIVE AND SUBJECTIVE
INTENSITY ESTIMATES LISTED ABOVE. ADDITIONALLY, A 301621Z ASCAT-C
PASS WHICH SHOWED 35-40 KNOT WINDS IN THE SOUTHERN AND WESTERN
PORTIONS OF THE CIRCULATION. THE ENVIRONMENT IS UNFAVORABLE AT THIS
POINT, WITH RELATIVELY COOL SSTS DUE TO UPWELLING, MODERATE TO HIGH
DEEP-LAYER SHEAR (AND EVEN STRONGER MID-LEVEL SHEAR) OFFSET BY
STRONG POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: THE SYSTEM IS EMBEDDED WITHIN A WEAK
STEERING PATTERN AND IS DRIFTING SLOWLY WESTWARD. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T2.5 - 35 KTS
   CIMSS ADT: 45 KTS AT 301800Z
   CIMSS AIDT: 40 KTS AT 301800Z
   CIMSS D-PRINT: 42 KTS AT 301800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: STRONG MID-LEVEL EASTERLY SHEAR

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 04B HAS CONTINUED TO
DRIFT SLOWLY TOWARDS THE WEST-SOUTHWEST THROUGH THE OVERNIGHT
HOURS, IN A GENERALLY WEAK STEERING PATTERN. THE SYSTEM LIES WITHIN
A VERY LARGE REGION OF CYCLONIC FLOW, WHICH IS FORECAST TO REMAIN
RELATIVELY STATIONARY FOR THE NEXT DAY OR TWO. TC 04B WILL IN A
NUTSHELL, REMAIN QUASI-STATIONARY OVER THE NEXT 12 TO 24 HOURS,
LIKELY TO DRIFT VERY SLOWLY, AT JUST A KNOT OR TWO, TOWARDS THE
WEST. HOWEVER, IT REMAINS POSSIBLE IT COULD PUSH BACK TO THE EAST
AND REMAIN OVER WATER OR STRADDLE THE COASTLINE FOR A BRIEF PERIOD
OF TIME. AFTER TAU 24, LOW-LEVEL RIDGING WILL BUILD IN ALONG THE
FRONT RANGE OF THE HIMALAYAS, WHICH WILL PUSH TC 04B ONTO A
WESTWARD TRACK. FORWARD SPEED OF THE REMNANTS OF TC 04B WILL
RAPIDLY ACCELERATE TO THE WEST AFTER TAU 48, AND MOVE BACK OVER
WATER IN THE NORTH ARABIAN SEA AFTER TAU 72. IN TERMS OF INTENSITY,
THE SYSTEM HAS STARTED TO RAPIDLY WEAKEN AFTER THE CONVECTION WAS
SHEARED OFF OVERNIGHT, WITH THE LATEST ASCAT DATA SUGGESTING A
MAXIMUM WIND OF 40 KNOTS IN THE SOUTHWESTERN QUADRANT. DUE TO THE
SLOW FORWARD SPEED OVER THE NEXT COUPLE OF DAYS, THE SYSTEM HAS
ALSO UPWELLED COOLER WATERS TO THE SURFACE, REDUCING THE ENERGY
AVAILABLE TO THE SYSTEM. THE MODERATE EASTERLY SHEAR AS WELL AS
PROXIMITY TO LAND, MEANS THE SYSTEM WILL CONTINUE TO WEAKEN
STEADILY. AFTER LANDFALL, THE SYSTEM WILL DISSIPATE OVER
SOUTHEASTERN INDIA WITHIN THE NEXT 36 HOURS. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN DISARRAY, WITH
A WIDE RANGE OF POSSIBLE OUTCOMES, DUE TO THE WEAK STEERING
ENVIRONMENT. FORECAST TRACKS RANGE FROM A NORTHWARD TRACK DEPICTED
BY THE GALWEM, A WESTWARD TRACK AS SHOWN BY THE ECWMF AND ECEPS, OR
AN EASTWARD TRACK SUCH AS INDICATED BY THE GFS. AFTER TAU 36
HOWEVER, THE GUIDANCE COMES INTO BETTER AGREEMENT, RAPIDLY PUSHING
THE SYSTEM WESTWARD, WITH THE BULK OF THE GUIDANCE INDICATING A
REEMERGENCE INTO THE NAS AFTER TAU 72. THE JTWC FORECAST REMAINS
CONSISTENT WITH THE PREVIOUS FORECAST AND ROUGHLY FOLLOWS THE
ECMWF, WITH LOW CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL STEADILY WEAKEN OVER THE COURSE OF THE
FORECAST, DISSIPATING BY TAU 36. 

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