Cyclogenesis off Uruguay and southern Brazil

Cyclogenesis off Uruguay and southern Brazil

2 April 2020 15:50 UTC and 29 April 13:20 UTC

Cyclogenesis off Uruguay and southern Brazil
Cyclogenesis off Uruguay and southern Brazil

Explosive cyclogenesis off the Uruguay coast and near southern Brazil in early April could be seen in satellite imagery.

Last Updated

10 November 2020

Published on

02 April 2020

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.

Image comparison

GOES-16 Airmass RGB compare1
compare2
 

Figure 1: GOES-16 composites for ABI channels around 1.6 µm,0.8 µm,0.5 µm (left) and Airmass RGB (right), 2 April 15:50 UTC.

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.

Image comparison

GOES-16 phase-solar RGB compare1
compare2
 

Figure 2: GOES-16 ABI airmass RGB (left) and phase-solar RGB (right) for 30 June at 17:10 UTC. The phase-solar RGB is based on R=0.86 µm-1.6 µm, G=0.8 µm, B=0.64 µm-0.86 µm.

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.

 Clockwise from upper left: Cloud phase composite, natural, colour-enhancement of 10.3 µm and Airmass at 13:20 UTC on 29 April.
Figure 3: Clockwise from upper left: Cloud phase composite, natural, colour-enhancement of 10.3 µm and Airmass at 13:20 UTC on 29 April.

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