Explosive cyclogenesis off the Uruguay coast and near southern Brazil in early April could be seen in satellite imagery.
By Néstor Santayana (INUMET) and José Prieto (EUMETSAT)
On 2 and 3 April, a cyclogenesis with explosive characteristics developed near the coast of Uruguay and southern Brazil. It deepened intensely, reaching 19 mb in 24 hours with a centre of less than 985 hPa.
This is the first extratropical cyclone with storm characteristics in 2020, near the coasts of Uruguay. Wind gusts reached 100 km/h on the coasts of the Departments of Canelones and Maldonado, and a even higher in the Department of Rocha (104 km/h). Cyclones are more common during the austral winter (from June to August) and the transition to spring.
The cyclone shown on the GOES-16 imagery on 2 April, caused an increase in the size of waves due to the persistent fetch wind from the southwesterly direction for at least 24 hours. Some houses in the coastal town of Aguas Dulces (Rocha) were badly damaged. Trees and electricity posts were also pulled down, the latter affecting more than 10,000 customers.
Well into the winter, on 30 June, prefrontal instability following a line pattern, with winds of 90-130 km/h, created a 400 km swath of damage in the southern states of Brazil and killed 12 people. The event can be characterised as a 'derecho' (explanation in Spanish), with downbursts, induced by, but separate from, the explosive cyclogenesis on the synoptic scale. The explosive cyclogenesis is rather a sudden drop of the surface pressure.
Figure 2 shows the GOES-16 airmass and phase depictions of the phenomenon. The most northern cloudy area over the south of Brazil gave birth to the derecho.
Between April and June that area recorded at least 11 cyclogenesis events, most of them following the same pattern. As did another instance on 29 April, as shown on Figure 3.
Ciclón extratropical tiró árboles y voló techos en Piriápolis; miles quedaron sin luz en Maldonado y Rocha (Semanario laprensa, in Spanish)
¡La foto! (Diario El Este, in Spanish)