Hi! My husband and I went to Belize in late August into early September about 5 years ago and only had one day of rain. I think it is just a matter of luck. It is the rainy season and hurricane season, but we didn't have any problems with the weather. If you go to www.weatherunderground.com you can research the history of Belizean weather for the dates you are planning on going.
Like I said, we had a fantastic 10 days and no weather problems except on our last day, it was overcast and a bit rainy.
Belize is a beautiful choice. I suggest instead of you staying in a beach hotel you spend time in a Jungle Resort and let them carry you on tours to the beach and other adventure/romantic trips. My reccommendation is a small jungle resort called the Black Orchid Resort. contact me and I can help you free of cost. email@example.com. I am in belize often
Oooohhhhh! I LOVE Belize! Look into staying on the island of Ambergris Caye. It's beautiful there. The Victoria House and Ramon's Village are EXCELLENT places to stay. Snorkeling and scuba diving are excellent too. It was so beautiful and the water there is crystal clear too! PM me if you want any more details. I went there in May 2005.
I went, long ago, and positively LOVED "Windy Hill Resort". Google it for more information. It's a luxury spot where you stay in self-contained little huts, and it's in the middle of a rainforest! Way cool.
If you stay in the rainforest, make sure you get your milaria (sp?) pills and start taking them a few weeks before you go. There are many mosquitos in the rainforest on the mainland and many carry milaria. It's a problem there. Just check with your doctor to make sure all of your vaccinations are up to date and you take all the necessary precautions.
I went to Belize about 2 years ago in mid-August. It was "rainy" season, but it really wasn't all that bad. On one day, we had a tour to visit some ruins and on the way there, it started POURING. We were on a boat and got absolutely drenched. lol. After 15 minutes though, it stopped and cleared up, so that we were able to walk around and take beautiful pictures. Even though it is rainy season, it's so off and on and so quick, that I don't think it will ruin any plans you have. I went for 10 days and it only rained a few times. I would recommend bringing a poncho or rain jacket w/ non-jean pants...your jeans will get soaked and will not dry easily. I wore convertible pants (zip off to make shorts) and it was great - dried easily and I took off the pants part when it got hot.