No matter what the season, chances are you will catch more sunshine in the San Juans [1] than anywhere else in the Puget Sound. Shielded by the Olympic and Vancouver Island mountains, the San Juans see less than 25 annual inches of rain, with the sun shining an average of 247 days a year.
The islands are immensely popular in the summer, particularly during the peak season of July and August when it is sunny and moderate— with temperatures rarely exceeding 85°F. If you plan a visit at these times, there may well be no room in the inn, and not a lot of mangers available either. Save yourself a lot of headaches by making reservations far in advance, even if you plan on camping.
At the older and more established B&Bs this means calling at least four months ahead of time for a midsummer weekend reservation. If you're looking for space on Memorial Day, the 4th of July, or Labor Day, make reservations up to a year in advance. Also plan on staying at least two nights, as most places on the islands require a minimum stay in the summer and sometimes year-round.
For the locals, September and October are the nicest months of the year: The tourists are gone, the weather is still warm and dry, with highs in the 60s and lows in the 40s or 50s, and the salmon are running. In the winter you'll find fewer fellow travelers and lower lodging rates (often 30 percent less), but the weather won't be quite as inviting and things won't be as green.
December is the wettest month, with 4.5 inches of rain on the average and temperatures in the low 40s. It rarely snows in the San Juans, and when it does it lasts but a few days. Still, winter holidays (especially Christmas to New Year’s) are likely to be booked well in advance.
For maps and other information before you arrive, contact the San Juan Islands Visitor Information Service, (360/468-3663 or 888/468-3701, www.guidetosanjuans.com [2]) and request Your Guide to the San Juan Islands, packed with up-to-date information.
Links:
[1] http://www.moon.com/destinations/washington/san-juan-islands
[2] http://www.guidetosanjuans.com