Atlantic water temps are going to be cool in Portugal, especially that time of year. As for places in the Mediterranean places I can think of may have visitors one might not want to encounter. Given that, my other suggest would be the Red Sea. Sharm-el-Sheikh or Hurghada in Eygpt. Water temp 25C so swimmable with warm air temps. Again could do some excursions from Hurghada to Luxor. Still might find visitors one might no to wanted encounter.