Advisories

WDPN32 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (NARRA) WARNING NR 
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.6N 107.3E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 115 NM SOUTHEAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 18W (NARRA) WITH WARMING CLOUD TOPS THAT ARE BEGINNING TO BE 
HEAVILY SHEARED OFF TO THE SOUTHWEST. A 241107Z GMI 89 GHZ MICROWAVE 
IMAGE REVEALED MINIMAL CONVECTIVE STRUCTURE TO THE WEST OF THE LOW-
LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH 
MEDIUM CONFIDENCE BASED ON THE GMI IMAGE AND ANIMATED EIR IMAGERY. THE 
INITIAL INTENSITY OF 40 KTS IS ASSESSED WIT MEDIUM CONFIDENCE BASED ON 
THE AGENCY DVORAK AND CIMSS INTENSITY ESTIMATES LISTED BELOW. 
ENVIRONMENTAL ANALYSIS INDICATES THAT 18W IS NOW IN A MARGINAL 
ENVIRONMENT CHARACTERIZED BY MODERATE EQUATORWARD OUTFLOW ALOFT, 
MODERATE TO HIGH (25-30 KTS) VERTICAL WIND SHEAR, DRY AIR ENTRAINMENT, 
AND WARM (29-30 C) SEA SURFACE TEMPERATURES

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: A COMPETING STEERING ENVIRONMENT WITH A
NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTH AND A SUBTROPICAL RIDGE (STR) 
TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 35 KTS AT 241210Z
   CIMSS AIDT: 36 KTS AT 241210Z
   CIMSS D-MINT: 37 KTS AT 241139Z
   CIMSS D-PRINT: 39 KTS AT 241210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE EAST

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: TS 18W IS FORECAST TO BEGIN TRACKING SLOWLY 
EASTWARD OVER THE NEXT 12 HOURS AS THE STR RIDGE TO THE NORTH WEAKENS 
AND THE NER TO THE SOUTH BECOMES THE PRIMARY STEERING MECHANISM. AFTER 
TAU 12, 18W IS EXPECTED TO TURN POLEWARD, USHERED BY THE NER BUILDING 
TO THE SOUTHEAST OF THE SYSTEM. LANDFALL WITHIN SOUTHERN CHINA IS 
FORECAST TO OCCUR AROUND TAU 48 NEAR THE LEIZHOU PENINSULA. REGARDING 
INTENSITY, 18W IS FORECAST TO BEGIN WEAKENING THROUGHOUT ITS APPROACH 
TO THE COAST OF CHINA AS EAST-NORTHEASTERLY SHEAR AND DRY AIR 
ENTRAINMENT BEGINS TO FURTHER INCREASE. AFTER LANDFALL, TERRAIN 
INTERACTION WILL QUICKLY WEAKEN THE VORTEX WITH DISSIPATION 
ANTICIPATED TO OCCUR NO LATER THAN TAU 60 AS THE REMNANT VORTEX TRACKS 
FURTHER INLAND. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE CONTINUES TO BE IN BETTER
AGREEMENT THIS MODEL RUN WITH THE ONLY OUTLIER BEING GALWEM, WHICH 
TRACK THE SYSTEM MUCH MORE QUICKLY INLAND THAN THE REMAINDER OF 
GUIDANCE. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL 
CONSENSUS WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE AGREES ON STEADY 
WEAKENING THROUGHOUT THE FORECAST PERIOD WITH NO NOTABLE OUTLIERS 
PRESENT. AS A RESULT, THE JTWC INTENSITY FORECAST IS ALSO PLACED NEAR 
THE CONSENSUS WITH MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM//
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