Brazilian corn farmers hoping for relief from drought were disappointed by weaker than expected rains this week, while frost expected in the state of Parana could bring further losses, weather forecasters said on Tuesday.

Much of the center-south of Brazil received below average rains in the past 30 days, a critical period for growing the country's second annual crop of corn that accounts for about three-quarters of the country's output, they said.

On Monday, agribusiness consultancy INTL FCStone revised Brazil's second corn harvest forecast down 1.75% to 72.6 million tonnes due to the drought.

"The risk of corn losses has increased a lot," said weather forecaster Marco Antonio dos Santos at consultancy Rural Clima.

According to Santos, the situation would result in lower yields and drag down the overall national output of second corn, which Rural Clima estimates will be 74 million tonnes this year.

Regarding the possibility of more rain over the coming days, the most recent simulations indicate there will not be a significant change in states like São Paulo, Minas Gerais and Goiás, Santos said.

On the other hand, the southern state of Paraná will receive between 10 to 15 millimeters of rain on Wednesday, said meteorologist Celso Oliveira at forecaster Somar Meteorologia.

Oliveira noted, however, that some farmers in Paraná have already recorded losses and filed claims with crop insurers.

According to the state's Department of Rural Economy (Deral), Paraná is forecast to produce 12.2 million tonnes of second corn this season.

That estimate factors in a loss of 600,000 tonnes from drought, Deral said, adding the first frosts of the year in the state are not expected to bring significant crop risk.

In Brazil's largest grain state of Mato Grosso, farmers cultivating corn along the BR-163 highway will receive up to 20 millimeters of rains this week, according to Oliveira.

In certain other parts of that state, rains will be scarcer, Oliveira said citing his weather models.