Nature will do as nature does. I would think as the trade winds ease, more sargassum "islands" will form and they will occasionally be brought into contact with the islands by winds and currents. It kind of is what it is and has been happening since the beginning of time. It won't ruin your trip unless you let it.
I remember growing up in Miami how the launching basin at CRYC used to get absolutely full of the stuff for months at a time during the summer. It got so thick at times you almost thought you could walk across it. If I recall correctly, we even convinced some poor trusting child try give it a try from time to time. It wasn't always appealing, but never stopped us from launching our Opti's and getting in a good day of sailing or anything else. In fact, we found fun and creative ways of enforcing group norms by tricking those who may have tested the groups rules or patience into hanging from the hoist hook and swinging them out over the seaweed as we called it and lowering them until they showed contrition. Ah, the good ole days. It also taught us the importance of boat maintenance and proper cleaning along with the value of maintaining a good coat of Teflon wax.
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