Summer: June to August is summer time in Grindavik. The weather is cool with a temperature ranging from 7 to 13 degrees Celsius, with July being the warmest month. There is minimal rainfall received during this season, making this the peak season.
Autumn: September to October is autumn in Grindavik. The average temperature is 8 degrees Celsius. The town receives the highest rainfall in the entire year, during this time. This is also low season for tourists in Grindavik.
Winter: November to March is winters in Grindavik. The weather gets pretty cold during this time as the temperature ranges from -2 to 4 degrees Celsius. This is basically off-season in Grindavik.
Spring: April to May is spring time in Grindavik. The temperature ranges from 6 to 9 degrees Celsius.
So, the best time to visit Grindavik is the summer season, in the months of June to August. This is also the best time to visit Blue Lagoon.