Southern Brazil will face a sequence of days of instability with a lot of rain in part of the region and storms. Strong to severe localized storms are anticipated and high rainfall accumulations aggravate the risk of flooding in some rivers whose basins in Rio Grande do Sul already had high volumes in last week’s instability episode.
The change of weather starts this Sunday. Instability areas should form overnight in Rio Grande do Sul and will gain a lot of strength from the end of the afternoon and evening with very high potential for strong storms of torrential rain, lightning, strong wind and especially hail. Very hot air quickly invades the state of Rio Grande do Sul, favoring instability.
The ingress of warm air will help to destabilize the atmosphere and form rain clouds. Isolated lightning strikes and risk of hail hit a few points in the northern half of the state, Santa Catarina and Paraná between the afternoon and evening of this Sunday, however the most intense instability should be organized in the west and south of Rio Grande do Sul in the second half of the day .
Initially charged clouds form over Uruguay and then in the west and south of Rio Grande do Sul. Instability is greatly intensified in these regions in the late afternoon and at night with heavy to locally torrential rain, many rays and storms. There will be hail and MetSul does not rule out that in some points it may be medium to large in size. Under very heavy clouds, the risk of isolated gales accompanying the storms can still be expected.
Instability begins to advance to the North on Sunday night and at the end of the day it should reach the Center of the State with heavy rain and storms. In Porto Alegre and the metropolitan region, on Sunday, which is sunny and will have an increase in clouds, the rain tends to arrive at the beginning of Monday.
Monday will be cloudy in Rio Grande do Sul with rain throughout the day in all regions. Moments of improvement are expected with openings of sun and dampening in the Western and Northern halves throughout the day, but the respite from instability is short-lived and these areas are back to having shocks in the sequence.
The largest volumes of rain should occur in parts of the West, Center, South and East of the state of Rio Grande do Sul during the second period, with high volumes in several locations due to sometimes strong showers and torrential rains. There is a high risk in Rio Grande do Sul of isolated storms on this Monday of strong wind and/or hail. Monday will have isolated instability in Santa Catarina and Paraná.
On Tuesday, many clouds cover Rio Grande do Sul and it still rains in most regions, but greater instability is expected in the Northern Half with a tendency to gradually improve from the West and the South. Some cities from the Center to the North Gaucho may start Tuesday with moderate to heavy rain, but the tendency is for rainfall to drop as the day goes on. Instability progresses to the North and increases in Santa Catarina and Paraná with rain in most regions of the two states and locally strong with risk of localized storms.
On Wednesday, the weather improves in most of Rio Grande do Sul and the sun appears again, but Santa Catarina and Paraná continue with more clouds and rain in several points. The largest volumes on Wednesday occur in the state of Paraná, which can register instability even on Thursday and Friday in a sequence of days of unstable weather and rain, which is beneficial in view of the drought and the need to increase the flow of the Iguaçu River and the affluence of Itaipu.
The map above shows the rainfall projection until 21:00 on Tuesday of the MetSul WRF model, which is available at subscriber with two daily updates on map section. The map below shows the rain trend for seven days of the German Icon model, which can also be consulted by the subscriber with four daily updates.
The risk of isolated thunderstorms in this episode of instability at the beginning of the week exists in the three southern states, but the greatest potential for thunderstorms will be in Rio Grande do Sul during the night of this Sunday and throughout Monday. In Santa Catarina and Paraná, isolated episodes may occur before, but the probability of localized storms is higher for Tuesday.
Even with the entry of a mass of cold air into Rio Grande do Sul, the weather will not set throughout the week in southern Brazil. The second half of this week should have periods of rain in several cities between the North of Rio Grande do Sul and Paraná, while in the southern half of Rio Grande do Sul the rain is now concentrated in the beginning of the week.