The best time to dive in the Similan Islands is from November to May. The islands are only open during these months. From June to October, local authorities close access to the Similan Islands because of the monsoon season and for conservation purposes. Within the period from November to May, several important events occur for optimal diving. In February, currents increase, attracting several pelagic species such as whale sharks and manta rays. Also during November to May, you can expect sea temperatures of 79 to 84°F (26 to 29°C). These warm temperatures mean that most likely you’ll be comfortable in a 3mm shorty or full wetsuit. Because of the remote location afforded to the Similan Islands, visibility is very good on average. While visibility can change from west to east, more than likely it will fall within the 82-130 feet (25-40m) range. Finally, surface conditions in the Similan Islands are generally stable from November to May. Dive site moorings are protected from the ocean open, and the journey to the islands is fairly easy during non-monsoon months.