Island weather is pretty much near perfect all the time! Although global warming can at times make things unpredictable, the driest months on the island are normally 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. (Traveling during this time? Definitely consider trip insurance.) Since 1930, at least 17 hurricanes & 18 tropical storm systems have affected Belize mainly per information here gathered from the US National Hurricane Archives); the latest was Hurricane Lisa hitting November 2, 2022. 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 a couple of suggested resources:
The Phoenix Resort, Wine de Vine, and Red Ginger family put together https://sanpedrowx.com/ to provide more accurate Ambergris Caye weather information, including an island webcam.
Windy is also a reliable resource.