Today is a fine spring day in Iceland with sunny skies and more such weather is predicted for the next few days. 
There will be little wind and although the temperature are only between 7 and 15 degrees C, if you find a sheltered sunny spot the sun can certainly be warm and the rays strong, so even if it seems ridiculous, sun protection is always a good idea. This is created when the cold ocean air blows towards the warmer temperatures inland.  
In some parts, there is some fog by the coastline.  If you’re looking for warmer temperatures, going further inland, away from the coastline is a good idea.