Subtropical Storm Biguá near the coast of Brazil
10-minute Full Disk scan GOES-16 (GOES-East) daytime True Color RGB + Nighttime Microphysics RGB images from the CSPP GeoSphere site (above) depicted the cyclonic (clockwise in the Southern Hemisphere) circulation associated with the formation of Subtropical Storm Biguá just off the coast of Rio Grande do Sul state in far southern Brazil during the 14th-16th December 2024 period.12-hourly surface analyses shown below (source) indicated that this subtropical storm developed as an area of low pressure (denoted by a red “B”) moved southeast across Rio Grande do Sul on 14th December, becoming classified as Subtropical Storm (“Tempestade Subtropical”) Biguá shortly after it moved offshore at 0000 UTC on 15th December. 24 hours later, Biguá was downgraded to a Subtropical Depression (“Depressao Subtropical”) at 0000 UTC on 16th December.
A sequence of ASCAT surface scatterometer winds (source) from Metop-B and Metop-C (below) showed that the compact low-level circulation center of Subtropical Storm Biguá remained just off the Brazilian coast on 15th December. The strongest winds were generally within the southern semicircle of the storm.