Island weather is pretty much near perfect all the time! The driest months on the island are from Christmas through May; if it does rain, it’s usually very short & sweet. June through December is called the “wet season”, but even then when it rains they are usually brief, although heavy, storms.
There is a hurricane/tropical storm season, which tends to be from August through October; since 1930, eight hurricanes & 17 tropical storm systems have affected Belize per information gathered from the US National Hurricane Archives. (See details here.) Belize’s National Emergency Management Organization keeps everyone well informed should there be any ‘situations’.
The more popular online weather sites often show the weather information for Belize City, even if you have asked about San Pedro, Ambergris Caye. Want to know what the weather’s really like on the island? Here are two great resources:
San Pedro dive master Elbert Greer of White Sands Dive Shop posts a photo and weather forecast daily on his FaceBook page here. For weather, he uses WindFinder which “specializes in wind, waves, tides and weather reports & forecasts for wind related sports like kitesurfing, windsurfing, surfing, sailing or paragliding and [his] personal favorite, diving. 20 mph can be the start of trouble 10 to 15 from the NE is normal” for San Pedro.
San Pedro Scoop blogger Rebecca gives great options for the best way to figure out the forecasts here. One site she mentions was set up by a local & will tell you the weather right this minute: SanPedroWeather.com