Late on Thursday afternoon at Interlagos, heavy rain started to fall.

The weather could be a precursor to a wet weekend at the Brazilian circuit, which a year ago hosted a famously drenched qualifying session.

The forecast for Friday is for a mainly fine day, with the chance of showers increasing later on and overnight.

Saturday could be showery and the outlook for Sunday is for better weather, but the conditions in Sao Paulo are often unpredictable — Thursday, for example, was expected to remain dry.

“It’s likely we will have some wet running this weekend,” said Renault driver Robert Kubica.

A third grand prix on the trot looks set to be disrupted by rain.

Bad weather affected the consecutive Japanese and Korean events recently, and rain is already disturbing the teams as they set up early this week at the Interlagos circuit in Brazil.

F1′s first sign of rain came at the weekend, when a golf tournament contested by Rubens Barrichello in Sao Carlos – a city of the Sao Paulo state – was cut short due to heavy rain.

And as the big teams including Ferrari set up at Interlagos on Monday, workers took cover inside the pit garages when a rain storm struck.

For the weekend, the initial forecasts predict possible showers across Friday and Saturday, with a reduced chance of rain for Sunday.

Last year’s Brazilian grand prix, held in mid October, was badly affected by rain, with delays protracting qualifying to an excruciating 160 minutes.

“There’s always a chance of rain,” said local Barrichello this week.

A wet weekend of weather is forecast for the 2010 Hungarian grand prix.

After rain intervened on many occasions during last weekend’s Hockenheim event, forecasters now expect the same sort of weather to feature at the Hungaroring, the twisty venue near Budapest that is set to stage its 25th consecutive formula one race.

An official report by Ferrari on Wednesday indicated that rain is forecast for Friday, thunderstorms on Saturday and perhaps a drier day for the race.

Another weather report backed the Italian team’s forecast, predicting a 50-50 probability of a dry race.

The weather in the Hungarian capital is already rainy, and it is not expected to improve on Thursday, when the circus is due to hurriedly recongregate in the paddock just three clear days after the German grand prix.

The Hungarian grand prix, staged in Mogyorod about 20 kilometres north of Budapest, is usually hot and dry.

The FIA reports that no changes to the circuit have been made since 2009 “other than routine maintenance”.