Tropical Storm NALGAE Advisory Fr, 28.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (NALGAE) WARNING NR
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 12.1N 128.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 457 NM EAST-SOUTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL IMAGERY (MSI) OVER THE PAST SEVERAL HOURS
INDICATES THAT DEEP CORE CONVECTION HAS BEGUN TO WRAP AROUND AN
IMPROVING LOW LEVEL CIRCULATION CENTER (LLCC), WHILE PERSISTENT
SUBSIDENCE IS KEEPING THE NORTHWESTERN QUADRANT LARGELY EXPOSED.
THE LLCC IS DEVELOPING ON THE WESTERN EXTENT OF WHAT HAD BEEN A
BROAD CIRCULATION, LEADING TO AN APPARENT ACCELERATION IN FORWARD
MOTION. OCEAN SURFACE WIND VECTOR DATA (OSWV) REMAINS ELUSIVE YET
AGAIN, HAMPERING ESTIMATES OF THE EXTENT OF 34 KNOT WINDS, BUT
POSITIONING WAS PLACED BASED ON MULTI-AGENCY DVORAK ESTIMATES OF
THE MSI INDICATED CENTER WITH MODERATE CONFIDENCE. A 272200Z SSMIS
91 GHZ PASS REVEALS INTENSE BANDING STRUCTURES WRAPPING ALONG THE
SOUTHWESTERN AND SOUTHEASTERN FLANKS INTO A LARGE BUT DEFINED
CENTER. THE INITIAL INTENSITY WAS MAINTAINED AT 40 KNOTS BASED ON
AGENCY FIX ESTIMATES OF 30 TO 35 KNOTS, WITH CIMSS ADT AT 39 KNOTS
AND A SATCON OF 38 KNOTS. EQUATORWARD OUTFLOW REMAINS ROBUST THANKS
TO A POINT SOURCE TO THE SOUTH, AND VERTICAL WIND SHEAR IS
FAVORABLE FOR ADDITIONAL DEVELOPMENT.
INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK, NO OSWV OR OTHER
WIND DATA TO SUPPORT
CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 38  KTS AT 271642Z
   CIMSS ADT: 39 KTS AT 272340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: NOW THAT THE LLCC IS TRACKABLE, IT IS APPARENT
THAT TS NALGAES CURRENT POSITION REMAINS SOUTH OF PRIOR FORECASTS,
AND IS PICKING UP SPEED AS IT MOVES CLOSER TO CENTRAL PHILIPPINES.
AS A RESULT, THE CURRENT TRACK HAS SHIFTED SOUTH, WITH LANDFALL NOW
EXPECTED BEFORE TAU 24 OVER THE BICOL REGION. THE SHORTENED
TIMELINE SHOULD LIMIT FURTHER INTENSIFICATION TO A PEAK OF 60
KNOTS. TS 26W WILL TRACK NORTHWARD OVER SOUTHERN LUZON BEFORE
ENTERING THE SOUTH CHINA SEA. A WEAKNESS IN THE STEERING RIDGE WILL
RESULT IN A TURN TO THE NORTH BY TAU 72. MODEL GUIDANCE INDICATES
THE TRACK WILL SLOW AFTER TAU 96 AS THE RIDGE RE-BUILDS AHEAD OF
TRACK. THERE IS A GREAT DEAL OF UNCERTAINTY AT THIS POINT AS
COMPETING STEERING INFLUENCES WILL DICTATE WHETHER NALGAE MOVES INTO
NORTHEASTERLY SURGE FLOW AND BEGINS TO WEAKEN AND TURN TO THE
NORTHWEST, OR WHETHER IT FOLLOWS THE EASTERN RIDGE ASSUMES CONTROL
AND TAKES TS 26W TO THE NORTHEAST.
MODEL DISCUSSION: DETERMINISTIC MULTI-MODEL GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 48, ALTHOUGH THERE IS SOME VARIABILITY IN TRACK
SPEEDS. HOWEVER, AFTER THAT TIME THERE IS A BIFURCATION IN THE
GUIDANCE AS DESCRIBED ABOVE. THE ECMWF AND GFS MODELS AND THEIR
ENSEMBLE MEANS ARE FAVORING A TURN TO THE NORTHWEST AT THE END OF THE
FORECAST.  APPROXIMATELY TWO-THIRDS OF ALL ENSEMBLE MEMBERS
FOLLOW THIS SOLUTION, WITH THE OTHER THIRD TRACKING TO THE NORTHEAST,
BUT THE EVENTUAL OUTCOME IS JUST BEYOND THE END OF THE CURRENT
FORECAST.  INTENSITY GUIDANCE WAS LOWER THIS CYCLE DUE TO TIMING OF
LANDFALL. THE CLEAR BIFURCATION IN MODEL GUIDANCE IN THE EXTENDED
PERIOD ALONG WITH POSSIBLE INTERACTION WITH THE NORTHEAST SURGE EVENT
LENDS LOW CONFIDENCE IN THE 72-120 HOUR JTWC TRACK AND
INTENSITY FORECAST.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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