Explosive cyclogenesis in the Río de la Plata and Atlantic Ocean

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Rapid development of a cyclogenesis caused strong winds and 11 m waves in the Atlantic Ocean. The coastal cities of Buenos Aires and Uruguay suffered severe damage.

Explosive cyclogenesis in the Río de la Plata and Atlantic Ocean
Date & Time
12 September 2016 00:38 UTC–15 September 10:38 UTC
Satellites
Metop A & B, GOES-13, Terra/Aqua, SARAL
Instruments
ASCAT, MODIS, ALtiKa
Channels/Products
Infrared, True Color RGB, ASCAT winds, Altimeter

By María Cecilia Villegas (Servicio Meteorológico Nacional - Argentina)

The central and northern areas of Argentina are characterised by the frequent development of cyclogenesis throughout the year. There are two main factors that cause this meteorological feature:

  1. The northern flow input from the semi-permanent anticyclone of the South Atlantic, which advects warm air and humidity from the Amazon basin and the Tropics, generating strong gradients of potential equivalent temperature.
  2. The Andes — a very high and extensive mountain range — favours the channeling of this flow, generating currents in jets of low layers and interacting with the upper level troughs.

Often called Litoral cyclogenesis, these features usually have displacements towards the southeast affecting the Rio de la Plata area and the Atlantic Ocean, where the decrease of the friction and latent heat release can cause rapid deepening, generating systems of severe storms.

Figure 2
 
Figure 2: MODIS True Color RGB overlaid with Metop-A ASCAT winds, 13 Sept 12:00 UTC, shows the concordance with the location of the low pressure system.

In this case in September 2016 a low pressure system initiated over the continent on 12 September, moved to the Río de la Plata and Atlantic Ocean zone with a rapid intensification and deepening, reaching rates of up to 1.16 hPa/hr and 22 hPa/24hrs, so it was considered explosive (according to analysis of observed data).

The GOES-13 infrared animation (MP4, 3 MB) shows the process of cyclogenesis from 12 September 00:38 UTC until 15 September 10:38 UTC. Figure 1 (top right, click to expand) is the Terra, MODIS True Color RGB, 14 Sept 12:55 UTC, which shows the centre of the cyclone located at approx 37S 48W.

On 13 September 13 at 00:00 UTC the low had already entered the Río de la Plata with values of 1002–999 hPa; and at 12:00 UTC it was positioned 37S 53W (over the Atlantic Ocean) with a centre of 981 hPa and a significant pressure gradient (Figure 2).

On 14 September at 00:00 UTC the system reached its maximum surface depth over the Atlantic Ocean, with values of 972 hPa and an intense gradient.

It was generating winds above 30 kt (55 km/h) on the coast of the Province of Buenos Aires, and 40–60 kt (74–111 km/h) to the northeast of the system, according to scatterometer data (Figure 3).

Figure 3
 
Figure 3: ASCAT on board Metop-B, ascending pass 14 Sept 00.55 UTC, shows 50 kt winds.

Using altimetry data and observations, we can estimate some waves were above eight meters in height, with some peaks of more than 11.5 m (Figure 4).

Although cyclogenesis is typical in the region, some 'extra' conditions are needed to generate a system of rapid development and deepening (explosive).

On one hand, the merging of the analysed system with a low pressure centre from the southwest; on the other hand, the blocking caused by the anticyclone to the east, with a centre of 1030 hPa.

The persistence of the low system, with a strong pressure gradient and corresponding high wind speed and high waves, caused by the blocking near the coast, caused a lot of damage in the coastal cities from Buenos Aires and Uruguay.

 
Figure 4
 
Figure 4: The altimeter (SARAL) data from 13 Sept 20:00 UTC, shows a correspondence with the model WIII-SHN/SMN, recording wave peaks above 11.5 m
 
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