My experience is that the weather forecasts for Belize City are more accurate for the mainland than for the cayes; we are out at sea, and the air doesn't have the chance to cool down so much at night, so when the forecast is rain for Belize City, there is just a 1 to 2 chance that it will also rain on AC. Also when it rains all day in BC, we usually have short showers. You could compare it to the weather differences between US costal areas, and inland!
Short