Tropical Storm CHABA Advisory Sa, 30.07.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (CHABA) WARNING NR
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 17.6N 114.7E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 283 NM SOUTH OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SPIRAL
BANDS OF FRAGMENTED, DEEP CONVECTION WRAPPING INTO AN ASSESSED LOW
LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED
WITH LOW CONFIDENCE BASED OF EIR LOOP AND MULTI-AGENCY FIXES. THE
INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED
ON THE IMPROVING CONVECTIVE STRUCTURE AS WELL AS A COMBINATION OF
AGENCY AND AUTOMATED DVORAK ESTIMATES.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 42 KTS AT 301119ZZ
   CIMSS ADT: 53 KTS AT 301740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TS CHABA IS FORECAST TO TRACK NORTHWESTWARD
UNDER FAVORABLE ENVIRONMENTAL CONDITIONS BEFORE MAKING LANDFALL EAST
OF THE LUICHOW PENINSULA AFTER TAU 36. THE FAVORABLE ENVIRONMENTAL
CONDITIONS ARE CHARACTERIZED BY MODERATE DIVERGENCE ALOFT, LOW-
MODERATE VERTICAL WIND SHEAR (10-15 KTS), AND VERY WARM SEA SURFACE
TEMPERATURES (SST) (30-31C), WHICH WILL ALLOW CHABA TO REACH A
POTENTIAL MAXIMUM INTENSITY OF 65 KNOTS BY TAU 24. THERE IS ALSO THE
POSSIBILITY OF RAPID INTENSIFICATION AFTER TAU 24 THROUGH TAU 36.
BETWEEN TAU 36 AND TAU 48, TS CHABA WILL BEGIN TO INTERACT WITH BOTH
THE ISLAND OF HAINAN AND EVENTUALLY MAINLAND CHINA SIGNIFICANTLY
DEGRADING THE INTENSITY AS THE SYSTEM CONTINUES TO TRACK
NORTHWESTWARD. BETWEEN TAU 48 AND TAU 72 TC 04W WILL MORE TRACK MORE
NORTHWARD AS FALLS UNDER THE INFLUENCE OF A MAJOR LONGWAVE TROUGH AND
BEGIN TO DISSIPATE DUE TO THE OROGRAPHIC IMPACTS OF SOUTHERN CHINA.
MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT WITH A
30NM SPREAD BY TAU 12, GRADUALLY INCREASING TO 90NM SPREAD BEFORE
LANDFALL AT TAU 42. FOR THIS REASON JTWC FORECAST TRACK IS PLACED
WITH MEDIUM CONFIDENCE. RELIABLE INTENSITY GUIDANCE IS IN GOOD
AGREEMENT WITH ALL MEMBERS SHOWING A STEADY INTENSIFICATION THROUGH
TAU 36 AFTER WHICH LAND INTERACTION AND EVENTUAL LANDFALL OCCURS
AND A SHARP DECREASE IN INTENSITY IS REFLECTED. MODEL GUIDANCE ALSO
AGREES OF THE POSSIBILITY FOR RAPID INTENSIFICATION THROUGH TAUS 24
THROUGH TAU 36.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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