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Subtropical Depression Four Forecast Discussion Number 4
2020-06-23 16:51:03| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Tue Jun 23 2020 000 WTNT44 KNHC 231450 TCDAT4 Subtropical Depression Four Discussion Number 4 NWS National Hurricane Center Miami FL AL042020 1100 AM AST Tue Jun 23 2020 GOES-16 visible satellite imagery shows that the depression's circulation has become better defined since yesterday, and the center is exposed just to the north of a band of convection mainly located within the southern semicircle. This convection is aligned along the Gulf Stream current, where instability is greatest, and the system appears a little more tropical than yesterday. However, the depression is still collocated with an upper-level low, and it will therefore retain the subtropical designation. The initial intensity remains 30 kt based on a ST1.5/25-30 kt classification from TAFB. A partial 1323 UTC ASCAT-B scatterometer pass showed winds near 30 kt to the southeast of the center, and we'll continue to monitor additional scatterometer data to see if there are winds any higher than that. The initial motion is still 11 kt, but the heading has turned east-northeastward at 65 degrees. The depression is forecast to turn back toward the northeast by this evening and begin accelerating on Wednesday within the prevailing mid-latitude flow. This track will take the system over increasingly colder water, placing it over sea surface temperatures less than 20 degrees Celsius by early Wednesday. Those ocean temperatures will make it difficult to support deep convection, and the updated NHC forecast now calls for the system to degenerate to a remnant low in 24 hours. Dissipation has been moved to 48 hours, although global model fields indicate that the system could open up into a trough by 36 hours before it moves past Newfoundland. The Ocean Prediction Center has provided 12-ft sea radii in the southern semicircle based on recent AltiKa and Jason-3 altimeter data. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 39.5N 62.1W 30 KT 35 MPH 12H 24/0000Z 40.6N 60.3W 30 KT 35 MPH 24H 24/1200Z 42.3N 58.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 25/0000Z 44.2N 55.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 25/1200Z...DISSIPATED $$ Forecaster Berg
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