Channel Islands National Park in March

April through June gives you the perfect storm of wildflowers, calm seas, and baby sea lions. The giant coreopsis blooms turn entire hillsides yellow in spring—it's genuinely spectacular. September and October bring the warmest water temperatures for snorkeling and the clearest visibility for spotting whales. Summer means crowds and higher boat prices, but also the most reliable weather. Winter storms make boat crossings dicey, though brave souls who make it over often have entire islands to themselves. Look, December through March can be magical if you don't mind cold, wet conditions and the real possibility of getting stranded an extra day due to weather.