Hi savannah!
I had my honeymoon in Cancun (albeit 7 years ago in November!) and we had a bit of rain during those 2weeks. When it did rain it poured down for about half hour, (we got caught walking back to the hotel from the shops and were drenched to the skin), but just as quick as the rain came, the sun then came out and everything dried up in about 10mins!
But its so warm there, its not like a horrible rain shower here in blighty, it passes quickly and then its back into the sun from the bar!
For a website to class a certain day as rainy/showers, it only needs to rain once on that day, so you may find all you have is the odd shower.
I'm off to Dom Rep in 2 months and its the rainiest month of the year! but i know we'll still have fun even if it does rain!
have a great time anyway x
tallulah x