In mid-May if the wind is out of the east it might be in the middle seventies up in Somes Sound or over in Bar Harbor, but 50 degrees at the entrance to Southwest Harbor. Once you get outside the islands the temps will drop to near the water temperature, which will most liklely be in the low 40s. Bass Harbor, where I am is generally 10-15 degrees cooler than Someville in the summer and 10 degree or more warmer in the winter. Fog also really drops the temp in the summer. The climate data are most likely for Bar Harbor, so the summer temps will be higher than than those in SW Harbor or Bass Harbor. Often my house can be in the fog with a temp in the mid-40s while it is near 70 and sunny in Southwest Harbor and in the mid-70s in Somesville