It rained for 14 hours in Rio yesterday, causing mudslides and wreaking havoc among the favelas (Brazil’s version of shanty towns) that cling to the city’s mountainsides. Many roads are submerged and at least 50 people have been killed. Meanwhile, thousands of motorists spent the night in their cars on log-jammed highways as floods sealed off the exits. And this is the site of future World Cup and Summer Olympics. Click here for raw ap video.

Does it rain in the Summer there...?

They just moved into fall, but apparently, yes, summer and fall are their rainy seasons.

From
http://www.brazil-travel-guide.com/Brazil-Best-Time.htm

Best time to visit Rio de Janeiro - Brazil

The high season in Rio is summer (December to March), but this high season is also the most crowded period and has the highest hotel prices. So, off-season (May-October) is also a good option, if you are looking for low hotel prices and don’t mind to face the risk of having some days of low temperatures: Rio’s winter temperatures stay around the 70sº F/20sº C, dipping occasionally below the 60ºF/15ºC (there are some short periods of low temperatures, and beach life isn’t agreeable).

Rainy days can be disturbing in a visit to Rio, but they are very unpredictable. They can happen even in the high season. The solution, when the rain comes unexpectedly, is to have alternatives as shopping or indoor visits or amusement - and Rio has plenty.

The story gets worse. At least 200 were killed in the mudslide form the Morro do Bumba favela across the bay from Rio, and the forecast is for rain later this afternoon and tomorrow. More video here.

Thanks Horus, your article says the 200 is in addition to the 153 others already dead, so that makes 353.
Now all they need is a smallish earthquake to level things out.