Tropical Storm CEMPAKA Advisory 7月18日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 10W (TEN) WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 20.6N 113.7E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 106 NM SOUTH-SOUTHWEST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 8 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING, COMPACT SYSTEM WITH CONVECTIVE BANDING WRAPPING INTO
A DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). AN 181058Z SSMIS
91GHZ MICROWAVE IMAGE ALSO SHOWS IMPROVED CONVECTIVE STRUCTURE AND
A DEFINED LLCC, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH
CONFIDENCE. AN 181321Z ASCAT-B BULLSEYE IMAGE REVEALS ASYMMETRIC
CIRCULATION WITH 25-30 KNOT WINDS OVER THE NORTHERN SEMICIRCLE AND
15-25 KNOT WINDS ELSEWHERE.     THE INITIAL INTENSITY OF 30 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT DATA.
ENVIRONMENTAL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH FAIR
OUTFLOW ALOFT, LOW VERTICAL WIND SHEAR AND WARM SST VALUES.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.0 - 25 KTS
   RJTD: T1.0 - 25 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: TD 10W IS FORECAST TO TRACK SLOWLY
WEST-NORTHWESTWARD TO WESTWARD THROUGH TAU 72 UNDER THE STEERING
INFLUENCE OF THE WEAK STR TO THE NORTH. AFTER TAU 72, THE SYSTEM
WILL SLOW UNDER COMPETING STEERING INFLUENCES AND TURN GRADUALLY
BACK TO THE SOUTHEAST UNDER THE STEERING INFLUENCE OF THE LOW-LEVEL
WESTERLY FLOW. IN GENERAL, THE NUMERICAL MODEL GUIDANCE SUPPORTS
THE FORECAST TRACK, HOWEVER, THERE IS A LARGE DEGREE OF SPREAD DUE
TO THE COMPLEX, EVOLVING SYNOPTIC STEERING ENVIRONMENT. TD 10W
SHOULD INTENSIFY QUICKLY TO A PEAK OF 55 KNOTS AT TAU 36 JUST PRIOR
TO LANDFALL WITH STEADY WEAKENING AS THE SYSTEM TRACKS OVER LAND.
TD 10W WILL LIKELY RE-INTENSIFY NEAR TAU 120 OR SHORTLY AFTER
REEMERGING BACK OVER WATER.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE SUPPORTS THE JTWC TRACK
FORECAST WITH LOW CONFIDENCE. CONFIDENCE IN THE JTWC INTENSITY
FORECAST IS MEDIUM WITH SOME UNCERTAINTY IN THE PEAK INTENSITY,
WHICH COULD BE SLIGHTLY HIGHER CONSIDERING THE COMPACT NATURE OF
THE SYSTEM AND THE TENDENCY FOR THESE TYPES OF SYSTEMS TO RAPIDLY
INTENSIFY. ADDITIONALLY, THERE IS ENOUGH UNCERTAINTY IN THE TRACK
AND THE POTENTIAL FOR A MORE PROLONGED TRACK OVER THE VERY WARM
WATER.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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