Tropical Storm NESAT Advisory Mo, 17.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (NESAT) WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 19.8N 116.8E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 394 NM NORTHWEST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
OVER THE PAST SIX HOURS, TYPHOON 23W (NESAT) DEVELOPED A LARGE
RAGGED EYE, BUT ONCE AGAIN THE EYE STRUCTURE HAS BECOME
CLOUD-FILLED. CURRENTLY ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS AN OVERALL SYMMETRICAL CENTRAL DENSE OVERCAST (CDO)
OBSCURING A COMPACT LOW LEVEL CIRCULATION CENTER (LLCC). ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES TY 23W IS
STRENGTHENING WITH CONVECTIVE BURSTS AND FLARING DEEP CONVECTIVE
CLOUD TOPS TEMPERATURES OF (-87C) AROUND THE SOUTHERN PERIPHERY OF
THE SYSTEM. ADDITIONALLY, WATER VAPOR IMAGERY SHOWS AN IMPROVING
ENVIRONMENT WITH MODERATE POLEWARD OUTFLOW STREAMING TOWARD THE
NORTHEAST AWAY FROM THE SYSTEMS CENTER. AN EARLIER 162245Z SSMIS 91
GHZ MICROWAVE IMAGE SHOWS A 75 NM DEEP CONVECTIVE CURVED BAND FULLY
SURROUNDING A 30 NM MICROWAVE EYE. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE MULTIPLE AGENCY FIX POSITIONS ALONG
WITH AN EXTRAPOLATED MICROWAVE EYE FEATURE DEPICTED BY THE SSMIS 37
GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY IS PLACED WITH MEDIUM
CONFIDENCE BASED ON SUBJECTIVE DVORAK INTENSITIES FROM PGTW T4.5,
RJTD T3.5, AND KNES T4.5. ADDITIONALLY, OBJECTIVE AUTOMATED DVORAK
ESTIMATES INTENSITIES FROM ADT IN PARTICULAR INDICATE 82 KNOTS, WHICH
IS SLIGHTLY HIGHER THAN SUBJECTIVE AGENCY DVORAK ESTIMATES.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: SOUTHEASTERN SIDE OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED OVER SOUTHEAST CHINA.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T4.5 - 77 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T4.5 - 77 KTS
   CIMSS SATCON: 78 KTS AT 170004Z
   CIMSS ADT: 82 KTS AT 170004Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: CURRENT ANALYSIS INDICATES A FAVORABLE
ENVIRONMENT WITH WARM SEA SURFACE TEMPERATURES (SSTS), MODERATE
POLEWARD AND EQUATORWARD OUTFLOW, AND MODERATE VERTICAL WIND SHEAR
(VWS), AS TYPHOON 23W (NESAT) CONTINUES TO STRENGTHEN AND TRACK
GENERALLY WESTWARD OVER THE PAST SIX HOURS. HOWEVER, THE STEERING
DIRECTION WILL TRANSITION MORE SOUTHWESTWARD AND CONTINUE THROUGH THE
NEXT 48 HOURS AS A SUBTOPICAL RIDGE OVER SOUTHEAST CHINA IS EXPECTED
TO BUILD AND EXTEND EASTWARD. AFTER TAU 48, THE STR THEN SHIFTS
FURTHER EASTWARD AND BUILDS OVER THE TAIWAN STRAIT. AS THIS OCCURS
THE RIDGE WILL THEN REORIENT TO A MORE NORTHWEST TO SOUTHEAST AXIS,
ALLOWING FOR THE SYSTEM TO TURN NORTHWESTWARD AND TRACK JUST SOUTH OF
HAINAN BY TAU 72. THE SYSTEM WILL CONTINUE ON A NORTHWESTWARD
DIRECTION BEFORE ULTIMATELY MAKING LANDFALL AND MOVING INLAND INTO
NORTHERN VIETNAM BY TAU 120. TY 23W IS FORECAST TO CONTINUE
STRENGTHENING AS DRY AIR WILL CONTINUE TO RECEDE AND MOISTEN OVER THE
NEXT 24-36 HOURS, WHILE THE SYSTEM MOVES OVER WARM SSTS WITH GOOD
OUTFLOW, ALLOWING A PEAK INTENSITY OF 90 KNOTS BY TAU 36. HOWEVER, BY
TAU 72 AND BEYOND, VERTICAL WIND SHEAR (VWS) ALONG WITH DRY AIR
AROUND THE SYSTEM IS FORECAST TO INCREASE AND AS A RESULT A STEADY
WEAKENING TREND IS EXPECTED BEFORE THE SYSTEM ULTIMATELY MAKES
LANDFALL INTO NORTHERN VIETNAM.
MODEL DISCUSSION: ENSEMBLE TRACK GUIDANCE FROM BOTH THE ECMWF
ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS) SOLUTIONS ARE IN GOOD
AGREEMENT WITH A FEW MEMBERS SHOWING LANDFALL INTO HAINAN, WITH THE
MAJORITY POSITIONED SOUTH, BEFORE SOME SPREAD BY TAU 120. NUMERICAL
TRACK GUIDANCE REMAINS IN GOOD AGREEMENT THROUGH TAU 72 WITH A
GRADUAL SPREAD TO 145 NM IN CROSS-TRACK SPREAD. BY TAU 120, CROSS-
TRACK AND ALONG TRACK SPREAD INCREASES SUBSTANTIALLY, LIKELY DUE TO
HOW MODEL TRACKERS ARE HANDLING THE LAND INTERACTION DIFFERENTLY.
OVERALL DETERMINISTIC AND ENSEMBLE GUIDANCE SUPPORTS THE JTWC
FORECAST TRACK. THE INTENSITY GUIDANCE REMAINS MIXED, WITH HWRF
REPRESENTING THE HIGH END OF INTENSITY GUIDANCE, WHILE AHNI, CTCI,
COTI AND DECAY SHIPS (NAVGEM AND GFS) REPRESENTS THE LOW END OF
INTENSITY GUIDANCE. GEFS ENSEMBLE INTENSITY GUIDANCE CONTINUES TO
SHOW MODEST PROBABILITIES OF MODERATE INTENSIFICATION OVER THE NEXT
36 HOURS. THE JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM
CONFIDENCE AND LIES CLOSE TO THE HWRF SOLUTION AND ABOVE THE
CONSENSUS MEAN.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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