Subtropical Storm Biguá hits Rio Grande do Sul, Brazil
Powerful winds and torrential rains produced by Subtropical Storm Biguá wreaked havoc across the Brazilian state of Rio Grande do Sul since its formation on Saturday, December 14, 2024. The storm toppled trees and power lines, and damaged homes, buildings, and infrastructure, leading to at least two injuries in Butiá.
Satellite image of Subtropical Storm Bigua at 13:20 UTC on December 15, 2024. Credit: NOAA/GOES-East, Zoom Earth, The Watchers
- Cyclone Biguá, a rare subtropical weather system for December, brought destructive winds of up to 100 km/h (62 mph) and torrential rain to Rio Grande do Sul, causing widespread damage and disruptions across the region.
- The cyclone caused power outages in at least five cities, including significant disruptions in Camaquã and Pelotas. Infrastructure damage included the collapse of a sports facility roof in Butiá, injuring two individuals.
- While the remnants of Biguá are expected to be absorbed by an extratropical cyclone, unstable weather with sporadic rain and wind gusts continues across parts of Rio Grande do Sul, especially in the eastern half.
Subtropical Storm Biguá formed off the coast of the Brazil – Uruguay border on Saturday, December 14, and was confirmed and named by the Brazilian Navy.
This is the first subtropical storm to impact the Brazilian state of Rio Grande do Sul since May 2022 when Subtropical Storm Yakecan stalled off the coast, setting record lows for the year and claiming two lives in Uruguay. It is also the first subtropical storm to impact Rio Grande do Sul in December.
Biguá brought heavy rain and winds of up to 100 km/h (62 mph), causing power outages across five cities. Significant power disruptions were reported in Camaquã and Pelotas, with teams actively working to restore electricity.
Power outages also impacted the valleys and metropolitan areas along the Serra region. The exact number of affected residents remains unclear.
In Butiá, the roof of a sports facility collapsed during a children’s event, injuring two people, one of whom had to be rescued from under the debris. Property damage was also reported in Triunfo, Encantado, and Pelotas, with fallen trees and roof damage documented.
The system brought very heavy rain to the southern and eastern parts of Rio Grande do Sul on Sunday, along with isolated strong gusts. Winds may have reached up to 100 km/h (62 mph) in the region on Sunday, December 15, but this cannot be confirmed due to limited coverage by automatic weather stations.
No data is available for the winds that may have affected the Taim reserve and Lagoa Mirim, where the strongest winds are believed to have occurred. In Chuí, the official station lacks functional wind-measuring equipment. Similarly, the government station in Mostardas, also on the coast, has no available data.
The system moved north along the eastern part of Rio Grande do Sul on Sunday, with wind gusts reaching the northern parts of Lagoa dos Patos, Porto Alegre, the metropolitan region, and the North Coast.
Around 14:00 local time (LT) on Sunday, an outer band of clouds preceding the subtropical cyclone’s vortex reached Porto Alegre, bringing heavy to torrential rain of short duration accompanied by strong to intense wind gusts.
Strong gusts impacted cities in the metropolitan area of Porto Alegre during the outer band’s passage, with a gust of 73 km/h (45 mph) recorded at a meteorological station in central Canoas at 14:30 LT.
The core of the cyclone’s circulation arrived in the Porto Alegre area around 16:00 LT, bringing overcast skies, rain, and persistent wind following hours of intermittent wind, sun, and isolated rain showers.
At 16:00 LT, the capital’s airport recorded wind gusts of 74 km/h (46 mph), coinciding with an increase in power outages across Porto Alegre.
The remnants of Biguá are expected to move away from Rio Grande do Sul on Monday, December 16, before being absorbed by an extratropical cyclone at sea. Meanwhile, weather conditions in Rio Grande do Sul remain unstable.
Clouds are covering many areas, particularly the eastern half, where rain and drizzle persist. Isolated heavy rain may occur, especially on Monday afternoon.
Despite the instability, temporary clearings may occur. In the Western Border and Northwest regions, sunny conditions prevail. Wind intensity is easing as the cyclone moves away, although sporadic gusts continue along the North Coast.
Biguá was the first subtropical cyclone to impact the region since May 2022 and the first to occur in December. It was also the second subtropical cyclone to form this year, following Akara, which developed off the southeast coast of Brazil in February.
Both Biguá and Akara were atypical cyclones named by the Brazilian Navy due to their subtropical nature.
Cyclones in this region typically lack subtropical or tropical characteristics. Extratropical cyclones, which are not named, are common in the South Atlantic and generally form at latitudes south of Rio Grande do Sul.
The key differences between extratropical and subtropical cyclones lie in their structure, location, and driving mechanisms.
Extratropical cyclones, which are common in this region, form in mid- to high latitudes. They are associated with cold and warm fronts and are fueled by temperature differences between air masses (horizontal thermal gradient). They have a cold core, with a central temperature lower than the surroundings, and well-defined meteorological fronts.
Subtropical cyclones form in subtropical latitudes and are fueled by a mix of horizontal thermal gradients and heat released during the condensation of water vapor.
They exhibit an intermediate or hybrid structure, with characteristics of both tropical and extratropical cyclones and feature a cold core at higher altitudes and a warm core at lower atmospheric levels.
References:
1 O QUE ESPERAR DO TEMPO APÓS OS ESTRAGOS DO CICLONE BIGUÁ – Metsul – December 16, 2024
2 QUANDO ACALMA O VENTO DO CICLONE BIGUÁ – Metsul – December 15, 2024
3 Cyclone Biguá Causes Chaos Across Southern Brazil – The Pinnacle Gazette – December 16, 2024
I am an Assistant Editor and Severe Weather & Science Journalist at The Watchers, specializing in real-time severe weather coverage, geophysical event reporting, and research-driven scientific analysis. You can reach me at rishav(at)watchers(.)news.
Hello, the first image from METSUL in this article is not about Cyclone Biguá, but rather about Cyclone Chido, which hit the French archipelago of Mayotte. Thank you.
Yes. Thanks!