Weather will likely play an important role when you plan your trip to Haukadalur, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually July and August with an average temp of 47°F, while the coldest months are December and January with an average of 26°F. The rainiest months in Haukadalur are January, September, February, and March, with each month seeing an average of 7 inches of rainfall.