In truth Blumenau is hot, at least in summer. It's in middle of a valley and have high humidity.
Right now temperatures are around 20°C and 10°C in cities bellow the mountain chain. The cities above it are colder, with temperatures ranging 20°C - 0°.
I took a look in Munich temperatures and they are 10°C less than Blumenau.
Quick fact:
The Oktoberfest in Blumenau was created to reconstruct the city from the most catastrophic flooding, the river was 15,3m over it's normal height. And the flooding took 10 days. In the next year the flooding got 15,6m. Anyway the biggest was in 1911 with 16,3m. And look that the river can go up to 7m without hitting the city.