Rio Grande do Sul is bracing for a significant weather event as the MetSul Meteorologia and the Instituto Nacional de Meteorologia (Inmet) have issued a red alert for excessive rainfall across the West, Center-West, and South regions of the state. This alert is effective from Thursday, May 8, 2025, until early Friday morning, May 9, 2025, indicating a high risk of flooding and inundations in the affected areas.
According to forecasts, rainfall is expected to exceed 200 mm within a mere 48 hours, with some regions potentially receiving upwards of 300 mm. The intense precipitation is being driven by a warm front currently impacting the region, but forecasters warn that a cold front will move in on Friday, further complicating the weather situation. This cold front could bring an additional 100 mm to 200 mm of rain in just one day, with localized areas experiencing 50 mm to 100 mm in under three hours.
By Thursday evening, rainfall totals had already reached alarming levels, with cities like São Gabriel recording 135 mm, Vila Nova do Sul at 133 mm, and Alegrete with 122 mm—all in less than 24 hours. The MetSul has noted that some cities could see rainfall amounts that are 200% of the historical monthly average for May, which raises concerns about severe disruptions in those areas.
"While we are expecting heavy rain, it is important to clarify that this event is not anticipated to reach the catastrophic levels seen in May 2024," a MetSul spokesperson emphasized, referring to the historic flooding that devastated the region last year. The current situation, while serious, is not expected to replicate the extreme conditions that led to widespread destruction.
In addition to the red alert, the Inmet has issued a yellow alert for the North, Northeast, and parts of the Metropolitan Region of Porto Alegre, including Canoas. This yellow alert, valid from 8 AM on May 8 until 7 PM on May 9, indicates that these areas could experience rainfall between 20 mm to 30 mm per hour, with daily totals reaching 50 mm. The risk of hail and strong winds between 40 km/h and 60 km/h is also present, although the likelihood of power outages or significant damage to crops remains low.
As the cold front approaches on Friday, May 9, heavy rain is expected across all regions of Rio Grande do Sul, particularly in the West, Central Depression, and the Southern Half, including areas near Pelotas and the Metropolitan Region of Porto Alegre. The forecast suggests that rainfall could range from 50 mm to 100 mm in less than three hours, with totals potentially reaching 100 mm to 150 mm within six hours.
Porto Alegre itself is under particular scrutiny, with models showing a significant risk of torrential rainfall throughout the day. The European Meteorological Center's model predicts a more modest 30 mm of rain, while the German Icon model forecasts much higher accumulations, potentially exceeding 100 mm during peak hours. This discrepancy among models highlights the uncertainty surrounding the exact amount of rainfall expected.
"In the best-case scenario, Porto Alegre will experience moderate to heavy rainfall, but in the worst case, we could see intense downpours leading to significant accumulations in a short period," noted the MetSul. They cautioned that if the worst-case scenario unfolds, the city could face numerous flooding incidents, with overflowing streams, power outages, and fallen trees disrupting daily life.
Despite these risks, the MetSul reassured residents that conditions are not expected to mirror the disastrous flooding of last May. On Thursday afternoon, the Guaíba River was measured at 0.77 meters, which is below the normal level for this time of year, indicating that the current situation is not as dire as last year's catastrophic floods.
In light of the forecasts, the Civil Defense of Rio Grande do Sul has also issued alerts for storms and flooding across the South, West, and Campanha regions. The main red alert, valid until noon on May 8, covers an area from Bagé to Santana do Livramento, warning of rain, wind, lightning, hail, and a very high risk of flooding. Additionally, an orange alert for high risk of localized flooding is in effect for parts of the Campanha and West regions, while yellow alerts for moderate risk are issued for rain, lightning, and localized flooding in the South and Middle Coast regions.
With these warnings in place, residents are urged to remain vigilant and prepared for possible disruptions. The MetSul emphasizes the importance of staying informed through official channels as the weather situation unfolds over the coming days.
As the state prepares for this significant weather event, the focus remains on ensuring the safety of residents while minimizing the impact of the expected heavy rainfall. Authorities are on standby to respond to any emergencies that may arise as conditions develop.
