Tropical Storm NESAT Advisory Sa, 15.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (TWENTYTHREE)
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 18.9N 126.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 412 NM NORTHEAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LARGE
CLUSTER OF DEEP CONVECTION OVER THE WESTERN PERIPHERY DISPLACED FROM
THE PARTIALLY EXPOSED LOW LEVEL CIRCULATION. AN EARLIER 142056Z SSMIS
91GHZ MICROWAVE IMAGE REVEALS SHALLOW BANDING WRAPPING INTO AN
ELONGATED LOW-LEVEL CIRCULATION CENTER (LLCC) POSITIONED ALONG THE
SOUTHEASTERN EDGE OF A CURVED CONVECTIVE BAND. THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED MSI AND THE
SSMIS IMAGE. A 142153Z SMAP WINDSPEED IMAGE SHOWS A SWATH OF 25-30
KNOT WINDS OVER THE NORTHERN AND SOUTHWESTERN SEMICIRCLE. THE
INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED
ON THE SMAP WIND SPEED IMAGE, ALONG WITH AGENCY DVORAK INTENSITY
ESTIMATES. ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE WITH
WEAK POLEWARD OUTFLOW, WARM (29-30C) SEA SURFACE TEMPERATURES (SSTS),
AND MODERATE (5-10KTS) VERTICAL WIND SHEAR (VWS).
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 29 KTS AT 142350Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TD 23W IS FORECAST TO TRACK WEST-NORTHWESTWARD
IN A MARGINALLY FAVORABLE ENVIRONMENT ALONG THE SOUTHWESTERN
PERIPHERY OF THE SUBTROPICAL RIDGE (STR) POSITIONED TO THE
NORTHEAST THROUGH TAU 36. BY TAU 48, THE STR IS EXPECTED TO REALIGN
TO A NORTHWEST-SOUTHEAST ORIENTATION WHILE A DEEP MIDLATITUDE
SHORTWAVE TROUGH IS FORECAST TO DIG OVER EASTERN CHINA, THESE
SYNOPTIC FEATURES WILL STEER THE SYSTEM IN A NORTHWEST DIRECTION
PASSING JUST NORTH OF LUZON. AFTER TAU 72, AS THE SHORTWAVE
TRANSITS EASTWARD, A DEEP LAYER RIDGE OVER EAST CHINA WILL THEN
BECOME THE MAIN STEERING FEATURE WHICH WILL ALSO INDUCE A
NORTHEASTERLY SURGE EVENT AT THE LOWER LEVELS. THIS WILL RESULT IN
THE SYSTEM TRACKING SOUTHWESTWARD AND THEN WESTWARD THROUGH THE
REMAINED OF THE FORECAST. TD 23W WILL STEADILY INTENSIFY THROUGH
TAU 36 WITH RAPID INTENSIFICATION POSSIBLE BETWEEN TAU 36 TO TAU 72,
AS POLEWARD OUTFLOW IMPROVES BY ENHANCED UPPER LEVEL WESTERLIES FROM
THE SHORTWAVE TROUGH, WHILE THE SYSTEM TRACKS OVER WARM (29-30C) SSTS
AND HIGH OCEAN HEAT CONTENT. BETWEEN TAU 96 AND TAU 120, THE
NORTHEASTERLY SURGE EVENT WILL INCREASE VERTICAL WIND SHEAR (VWS)
WHILE INCREASING DRY AIR AROUND THE SYSTEM WHICH WILL RESULT IN
STEADY WEAKENING THROUGH THE END OF THE FORECAST.
MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT
THROUGH TAU 48 WITH ONLY A 150 NM SPREAD IN SOLUTIONS, WITH A
LARGER SPREAD OF 150-200NM FROM TAU 72 TO TAU 120. THROUGH TAU 72
BOTH THE AVNI (GFS) AND AEMI (GFS ENSEMBLE) TRACKERS REPRESENT THE
SOUTHERN PERIPHERY OF GUIDANCE, WHILE ECMI (ECMWF) AND EEMN (ECMWF
ENSEMBLE) TRACKERS MAKE UP THE NORTHERN EDGE OF THE GUIDANCE
ENVELOPE. THE BULK OF THE ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE
(GEFS) SOLUTIONS SUPPORT THE JTWC FORECAST TRACK THROUGH TAU 48,
WITH INCREASING UNCERTAINLY AFTER TAU 72. THEREFORE, THE JTWC
FORECAST TRACK IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS
WITH MEDIUM CONFIDENCE. THE RELIABLE INTENSITY GUIDANCE REMAINS IN
FAIR AGREEMENT AND SUPPORTS AN INTENSIFICATION PHASE WITH HWRF ON
THE HIGH END OF THE INTENSITY GUIDANCE INDICATING A PEAK INTENSITY
NEAR 85 KNOTS, ABOVE THE INTENSITY CONSENSUS PEAK OF 75 KNOTS. GEFS
INDICATES HIGH PROBABILITY OF MODERATE INTENSIFICATION AND A 10
PERCENT CHANCE OF RAPID INTENSIFICATION (RI) BETWEEN TAU 48 AND TAU
72. AFTER TAU 72 THE INTENSITY GUIDANCE INCREASES IN UNCERTAINTY DUE
TO HOW THE SYSTEM INTERACTS WITH THE MODERATE NORTHEAST SURGE EVENT.
THEREFORE, THE JTWC FORECAST INTENSITY IS PLACED WITH LOW CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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