The Caribbean climate varies little throughout the year, and it's almost always sunny, even during the rainy season. If it drops below 70 you might see sweatshirts come on. For Caribbean vacations, high season has commonly lasted from December to April, when bad weather to the north sends tourists towards the islands in droves. Especially around Christmas time, you'd better be booking far in the future if you want a decent Caribbean vacation deal. Prices fluctuate throughout the year - the islands are notorious for having deals appear and disappear with little to no warning. Prices are considerably higher during these winter months, too, when a discount Caribbean vacation is virtually unknown. Expect to pay at least a couple hundred more for your plane ticket, and a lot more depending on where you are staying.
The winter months in the Caribbean can be a hectic mess. Half the known world seems to want to take their winter breaks here, and with many of the islands (such as Puerto Rico and Aruba) becoming increasingly popular as spring break locales, Caribbean vacations can often be full of the sort of people you had hoped to leave behind. However, anyone serious about getting away from it all (the goal of so many Caribbean vacations) will have to do only a little bit of work to find solitude, though it is harder if you book one of the all-inclusive resorts. But if you are planning on staying at a resort, solitude or a discount Caribbean vacation are probably not your intentions anyway.
For those who can wait until their own hometowns begin to heat up, the islands thin out a bit starting in May. You will see cheaper prices on everything from hotel stays to the food carts in the street. On islands that are already amongst the cheapest in the region, such as Jamaica or Puerto Rico, this can make for a fairly cheap summer stop. Discount Caribbean vacations become a lot more feasible, especially as the calendar passes August - between then and November is the lowest of the low season and though you are no longer guaranteed top-quality entertainment at many of the resorts (or for some restaurants to even be open), many travelers see little difference between Caribbean vacations taken in October versus those taken in March. Another selling point of the low season is that many island festivals and carnivals have been shifted to the off months in order to keep crowds down.
The only real danger of getting a Caribbean vacation deal for the off months is the possibility of hurricanes. While the southern islands are traditionally safe, hurricanes have been known to hit the upper islands - the most famous being Hurricane Ivan, that ravaged Grenada in 1994. But this is a fairly unlikely scenario, and hurricanes don't just appear out of nowhere - keep on top of the local news and you won't have to worry about any tropical storms.