Best time to come to San Blas
Most gringos come between the beginning of November until the end of April.  Usually the weather is beautiful during these months - sunny, 75 to 80 and cooler at night.  However for the last 2 years, perhaps due to climate change, it hasn't cooled down until the end of November. It starts to heat up in May and June - maybe 90 to 95, humid with no rain.  July through October is the rainy season with brilliant thunder and lightening storms almost daily - usually in the late afternoons or at night.  People always told me not to come down here in the summer.  When I finally tried it, I loved it.  I like it hot.  In the summer months the ocean water feels like a lukewarm bathtub.  Also, summer is when the good waves come.  Christmas and the weeks before and after Easter are the only times you would need reservations.   I don't recommend these times, unless you have no choice, or you enjoy crowds.  There are many festivals here.  My favorite is San Blas Day on February 3rd when they take the old wooden statue of San-Blas for a boat ride followed by incredible fireworks in the plaza.