Coastal Maine has been en-veloped in fog for weeks, as you may have noticed – or even agonized over if you had hoped for a lot of sailing or seashore picnics on sparkling, crystal-clear days. Sometimes it’s there in the morning, lifts a little and creeps back in by early afternoon. Sometimes it lingers longer. Some coastal motels have their vacancy signs out and the restaurant business is down. Some people have even canceled plans for a Maine vacation.

What’s causing so much fog? Professor Andrew Thomas, an oceanographer at the University of Maine, cites three factors: a long period of moist air, wind mainly from the southwest, and sea surface temperatures from Eastport to Portland about 1 to 1.5 degrees celsius below average. That’s plenty to make a difference. Occasional offshore breezes push the moist air over the cold ocean, and the fog rises like a wall of cotton wool.

A satellite passes over the Gulf of Maine at least once a day and checks the temperature of the surface water by measuring heat radiation. The university’s Satellite Oceanographic Data Lab process those findings and every eight days produces a colored map of the gulf. Red areas are warmer and blue areas are colder than the 20-year average.

The latest report, for the period ending July 11, shows light blue along the Maine coast. Earlier maps show that the water turned colder starting in mid-May, after earlier periods when it was 2 degrees warmer than average.

In July of the past two years, the water was as much as 2 degrees warmer than average. In 2001 and 2000, it was a degree or so colder.

Dr. Thomas says what’s needed is a wind shift. One of those brisk northwest winds that usually clears the air once in a while but has been missing this summer could bring back those beautiful fog-free days. The National Weather Service has been looking for a string of dry days starting about Sunday.

But don’t hold your breath. This has been a foggy summer so far and it may not really lift anytime soon.