Tropical Storm ATSANI Advisory sáb, 07-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (ATSANI) WARNING NR
032//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 23W (ATSANI), LOCATED APPROXIMATELY 224 NM
SOUTH OF TAIPEI, TAIWAN, HAS TRACKED WEST-NORTHWESTWARD AT 10 KNOTS
(KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS BUILDING CONVECTION OBSCURING A LOW LEVEL
CIRCULATION CENTER (LLCC). BASED ON THE MSI, RADAR IMAGERY, AND AN
EXTRAPOLATION OF A 060446Z AMSR2 89 GHZ MICROWAVE IMAGE SHOWING
TIGHT BANDING WRAPPING INTO A LLCC, THERE IS GOOD CONFIDENCE IN THE
INITIAL POSITION. THE INITIAL INTENSITY REMAINS ASSESSED AT 45 KTS
WITH GOOD CONFIDENCE BASED ON MULTI-AGENCY DVORAK CURRENT INTENSITY
ESTIMATES OF T3.0 (45 KTS, PGTW/RJTD) ALONG WITH A 060146Z CIMSS
SATELLITE CONSENSUS INTENSITY ESTIMATE OF 45 KTS AND RECENT ASCAT
DATA SHOWING SWATHS OF 40-45 KT WINDS IN THE NORTHERN QUADRANT.
OVERALL, TS 23W REMAINS IN A HIGHLY CONDUCIVE ENVIRONMENT FOR
DEVELOPMENT CHARACTERIZED BY LOW (5-10 KTS) VERTICAL WIND SHEAR
(VWS), WARM (27-28 CELSIUS) SEA SURFACE TEMPERATURES (SST), AND
POLEWARD AND EQUATORWARD OUTFLOW CHANNELS. TS 23W IS TRACKING ALONG
THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED
TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 23W IS EXPECTED TO TRACK GENERALLY WEST-NORTHWESTWARD
THROUGH TAU 12 AS IT TRANSITS ALONG THE SOUTHWESTERN PERIPHERY OF
THE STR, INTENSIFYING TO 55 KTS DUE TO PERSISTENT FAVORABLE
ENVIRONMENTAL CONDITIONS. AFTERWARDS, THE SYSTEM SHOULD TURN TO A
WESTWARD THEN SOUTHWESTWARD TRACK AS A STR POSITIONED OVER CENTRAL
CHINA TAKES OVER AS THE PRIMARY STEERING MECHANISM. DURING THIS
TIME, INCREASING VWS WILL BEGIN TO WEAKEN THE SYSTEM AS IT TRACKS
SOUTHWESTWARD OVER SLIGHTLY COOLER (26-27 CELSIUS) SST. THE SYSTEM
IS EXPECTED TO FULLY DISSIPATE OVER WATER BY TAU 72 AS IT ENCOUNTERS
CONTINUED HIGH (30+ KT) VWS. NUMERICAL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 36. HOWEVER, THE MODEL SOLUTIONS BEGIN TO DIVERGE
AFTERWARDS, LIKELY DUE TO DIFFERENCES IN THE TIMING WHEN THE STR
OVER CENTRAL CHINA BECOMES THE PRIMARY STEERING MECHANISM.
ADDITIONALLY, SEVERAL MODELS MAINTAIN A WESTWARD TRACK RATHER THAN
TURNING THE SYSTEM SOUTHWESTWARD AFTER TAU 24. BASED ON THIS
UNCERTAINTY, THERE IS OVERALL POOR CONFIDENCE IN THE JTWC FORECAST
TRACK WHICH LIES NEAR THE MULTI-MODEL CONSENSUS.//
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