Outdoor weddings are beautiful and fun. And if you are getting married at the Caribbean in a beachfront venue it will be dreamy. But you should have in mind that tropical weather is very hot and humid.
When selecting your wedding cake's design you must be sure if your selected venue have air conditioning system or not, and at what time of the day you will be getting married (afternoons are slightly cooler than the mid-day). The problem is, some couvertures don't behave well in hot or humid weathers. Fondant cakes are beautiful and have a very neat finish, but it tends to melt with humidity. So, if you are in love with a design that have ruffles or frills, know that they can melt even before you arrive at the venue if the day is really humid and your venue doesn't have air conditioning. Buttercream, otherwise, behaves well with humidity, but it is recommended to have it under a roof, tree, or tent. If the day is too hot and it's getting direct light from the sun, it can melt too. Although in late afternoon you should not worry about this.
So, when planning your wedding be sure your venue goes along with the cake design you want. Ask your cake decorator, he/she will give you ideas and suggestions. Also, check at what time they can deliver your cake. Some beachfront wedding venues have air conditioning system, but they will likely turn it on just one or one and a half hour before the wedding starts. If a buttercream or fondant cake is deliver on a hot room for a long time (and remember, Caribbean weather is reaallly hot!) it could be ruined, melt, or even worst, the cake itself can ferments and nobody will be able to eat it. The cake is the second attraction at a wedding, after the bride. Everyone expects to see a beautiful piece. So don't forget to have in mind all these details.