39°C?, that's really hot. Our Summers average at 15°C (59F). The hottest Summer days can sometimes be over 30°C (86F), and the coldest about 10°C (50F). Depending on your location in Finland, the lowest temperature in Summer can even go below 0°C.

The termic Summer in Finland is when the average temperature stays above 10°C.

My figures may be quite off. Wikipedia may have somewhat more accurate statistics.