Extratropical cyclone on the Rio de la Plata basin

By: izmir2 , 5:33 AM GMT on August 26, 2014

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An intense extratropical cyclone has formed off Bahía Blanca, Argentina and moved roughly along the southern coast of the Buenos Aires province, bringing gusty weather throughout the province, as well as the southern coastal provinces of Uruguay and southernmost state of Rio Grande do Sul in Brazil.


Figure 1. IR4 image of the cyclone at 12:22am (UTC-3) August 26. (Credit: Weather Underground)

At 8pm UTC, 44 kt (80km/h) wind gusts were recorded at the Air Force Metereological Service in Montevideo, where very intense gusts were reported from the city's esplanade. In Argentina, the Aeroparque airport reported winds between 37-43 kt (70-80 km/h).


Figure 2. Short wave image of the cyclone as of August 26, 04:08 UTC. (Credit: RAMDSIS)

Both Argentina and Uruguay meteorological services and Brazil's privately-owned Metsul issued marine and coastal high wind warnings as hurricane-force (over 65 kt, 120 km/h) wind gusts were expected for Monday and Tuesday in the Rio de la Plata basin (a.k.a River Plate).

In the Southern Hemisphere, August marks the last stretch of winter and the beginning of occurrence of extratropical cyclones due to the interaction between tropical and polar air masses at this mid-latitude sector of South America. Therefore, a few such cyclones are usual events from late winter to mid spring (August to November) and less so, from mid summer to mid autumn (January to April).

The late August event is locally known as the Santa Rosa storm as it happens around August 30, day of St Rose of Lima in Catholic liturgy. Though climatology shows the phenomenon is not yearly regular, the storm is the first one by the end of the winter.


Figure 3. A similar extratropical cyclone on September 4, 2003. (Credit: Wikimedia Commons)

August 27 update


In Uruguay, the storm left more than 19,000 Montevideo residents without power and a large number of trees toppled 51 kt (95 km/h) wind gusts. The local harbour was also closed for several hours during the harshest part of the storm. In Punta del Este and Colonia del Sacramento, winds peaked 60 and 55 kt (111 and 101 km/h) respectively.(1)


Figure 4. Trees toppled by high winds in Montevideo. (Credit: El Observador)

In Argentina, hail was recorded in Buenos Aires and hurricane-force winds lashed Mar del Plata, where 15 ft (5 m) waves battered the coast for several hours. Besides, classes were suspended at schools due to the dangerous weather conditions.(2)


Figure 5. 15 ft waves hitting the Mar del Plata esplanade. (Credit: Puntonoticias)

Though a few hundred people had to be evacuated in Argentina, neither of the two countries reported casualties related to the storm.

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1. Barefootontherocks
2:01 PM GMT on August 26, 2014
Thanks. Interesting, the extropical stormy weather and the background on the Santa Rosa storms in this part of the world. Your photos prompted me to learn a little more about Uruguay, which led me to read about a man named Jose Enrique Rodo. Thanks again for the lessons in weather, history, geography and all.
Member Since: April 29, 2006 Posts: 158 Comments: 19346

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About izmir2

Hey! My name is Dan and I'm a weather enthusiast. I'm here to blog important information related to the Rio de la Plata basin weather.

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