Synoptic comparison between two cases of subtropical cyclones in the South coast of Brazil

Abstract

Subtropical Cyclones are low-pressure systems that occur in tropical or subtropical latitudes and that have characteristics of both tropical cyclones and extratropical cyclones. The subtropical class also has a thermodynamic forcing near the surface resulting from heat and humidity flows from the warm ocean. The objective of this study is to make a comparison between two cases of subtropical cyclones that occurred on the south coast of Brazil during the end of spring and summer periods in the Southern Hemisphere. The chosen cases were SC Cari and SC Eçai, which occurred respectively from March 10th to 13th of 2015 and from December 3rd to 6th of 2016. This study was carried out through the analysis of meteorological fields employing the ERA5 reanalysis data along with GOES-13 satellite imagery. In spite of both systems occurring on a similar spatial domain, their different atmospheric characteristics have an important part in their origin, intensity and trajectory. Their trajectories were of interest because of their uncommonness, where Cari moved at first towards the continent presenting risks to the society and only later moving towards the ocean till its dissipation. And Eçai formed over the land as a thermal low that moved towards the ocean gaining strength as it found warm waters, finding a new and more favorable environment.