Hi RachelAnne,
I'm on the island, Its hot, I'm sweating. I'm here looking at the sky , its blue the sun is bright and there are some fluffy white clouds.
I have on shorts and bare feet as does every one I see.
San Ignacio is in the hills and I take a light jacket when i visit there because sometimes ...not often its cool at night.
Belize City forecast doesn't really reflect/pertain to San Ignacio.
It gets 100 inches a year up in the hills and I always expect to be rained on a little but its warm rain and never seems to last long.

White Sands Dive Shop
https://whitesandsdiveshop.com/