Look at dew point. If dew point and temperature are within 4 degrees of each other, you are on the verge of fog. In a kayak consider that sitting on the water without wind there's often a close relationship between water temperature and air temperature.
Anyway, look up the relationship between dew point and temperature.
I don't know much about marine weather forecasting, but there is lots of information on this for airplane pilots. The 4 degree rule is important for VFR pilots to keep in mind, especially flying in California during "May Gray's" and "June Gloom" conditions. Runways can quickly fog in, and that sucks if you can't see where you're landing!
And here we are .... almost in May. We have had lots of rain recently so we are pretty well soaked around here. As temperatures rise for summer, this moisture goes into the air. This might be a good year for fog and muggy weather for the next two months. That also depends on how fast the heat season comes in for spring and summer. This past few days has been a wonderful early heat spell. Warm air holds more moisture that can precipitate out as fog or "low onshore flow" etc. For the years we have wet weather and moist air in May/June, it seems to last forever, but it almost always burns off and drys out by July.
Maybe this will help:
http://theweatherprediction.com/fog/