Alex, the weather report for Belize City, is rarely a good indicator of what is happening at Ambergris.
You are going to be going on your holiday, come what may. Why stress yourself about it now? Usually, if there is any rain it is brief showers and then the sun comes out and it is quite lovely again.
You will enjoy yourself, rain or shine, though no question, shine is better.
Hey, Belizeit, mon. Chill.