Chiloé is often rainy and that is simply its nature — the archipelago sits in the Chilean Lake District's weather shadow and receives heavy rainfall year-round. Summer (December-March) is the driest and warmest period, with temperatures reaching 20°C on good days. Even in summer, the sky can close in quickly and rain is never far away. Bring waterproof gear whatever time of year you come.
The best time to visit for penguin watching is October through March, when the Magellanic penguins are nesting at Puñihuil. For the potato market and traditional food, any time of year works; the main harvest festivals happen in April. The UNESCO churches are accessible year-round. The national park is most rewarding in summer when the forest trails are drier and the Pacific beaches are occasionally visible through the mist.
Avoid Easter Week if you dislike crowds: Castro fills with Chilean domestic tourists and accommodation prices rise sharply.