One of the first things you think about when selecting a destination for your vacation is what the weather is going to be like. If you have chosen Cancun then there is nothing to worry about, you are almost guaranteed good weather, or at least, you would be very unlucky to have bad conditions throughout the whole time you are staying here. In fact, the climate in Cancun is considered the best in the Caribbean, owing to the high number of clear sunny days per year, which is about 250 on average.
The temperatures are hot and balmy no matter what time of year you take a vacation. Winter is very pleasant as temperatures range from 81ºF (27ºC) to 66ºF (19ºC), the lower temperatures being at night. In summer it rarely goes above 91ºF (33ºC) and fluctuates between 90ºF (32ºC) and 75ºF (24ºC), which is not too hot for families and older visitors. What is definitely a benefit is the sea temperature which only changes a few of degrees between 80ºF (26ºC) and 83ºF (28ºC). There is nothing like swimming in the sea during a winter break.
You will be very lucky with rain in Cancun too. While it could well rain while you are on vacation, it is very unlikely to spoil your break. Mostly, rain in Cancun is light to moderate and there is no strictly defined rainy season as such. It can get quite humid, which is fine while sat by a cool refreshing swimming pool or by the sea. Statistics show that Cancun experiences about 60 days of rain each year, so really it should not be a hindrance to your enjoyment.
Like any Caribbean destination, Cancun can be subject to hurricanes and storms during the hurricane season from June to November although they are not very common. You are more likely to experience the rain that comes off the tail of a hurricane further out in the Caribbean sea.