July and August are the hottest months across the Mediterranean, with highs regularly topping 90°F in Greece, Southern Italy, and along the Adriatic coast. Combined with peak European summer-holiday travel, this is also when ports are at their most crowded — Santorini, Dubrovnik, and Venice see the heaviest foot traffic of the year.
Cruisers sensitive to heat or crowds generally do better in May, June, or September, when temperatures are still warm and pleasant but a few degrees cooler and shore excursions are noticeably less congested.
For a July or August sailing, plan port days around the heat: book morning excursions, carry more water than feels necessary, and expect long lines at the most photographed viewpoints.