I found a FB (Facebook) page which gives satellite information on the sargassum situation in Cancun/Riviera Maya.  Given the satellite pics, there is a huge amount of brown algae headed into the Riviera Maya area in the next few days.  If you want to keep track of this type of information, you will need access to Facebook.  In the FB search box/bar, type in Red de Monitoreo del Sargazo Cancún.  Hope this helps for those of you wanting into about the algae situation prior to your vacation.