Similan Islands in December

The islands close completely from May 15 to October 15 due to monsoon conditions. Your window runs November through April, with distinct seasons within that period. November and December offer the calmest seas and best visibility for diving - often 35-40 meters. But expect higher prices and crowds, especially around Christmas. January through March delivers the most reliable weather with minimal rain and gentle breezes. This is peak season, so book accommodations and liveaboards well ahead. April sees rising temperatures (35°C daily) and occasional afternoon storms, but fewer crowds and better deals. The shoulder months of late October and early May can be spectacular if weather cooperates, but you're gambling on conditions. Water temperature stays warm year-round at 27-29°C. Northeast monsoon winds from December to February can make some dive sites choppy, but generally create better visibility.