Sea Temperature by Month

The table shows approximate typical surface temperatures around central Dalmatia (Split and the nearby islands). They are rounded ranges for general planning rather than measurements for any particular year, and individual days can fall outside them.

The sea warms more slowly than the air in spring and holds its heat longer in autumn. That is why late September can feel better for swimming than early June, even when the air is cooler.

Sea temperature changes with location, depth, weather and year. A few patterns are useful to know:

• Shallow, sheltered bays warm up faster on calm, sunny days than open channels and deep water.
• Strong wind stirs the sea. After a few days of fresh wind, cooler water from below can mix up to the surface near the coast and the temperature can drop for a while.
• Depth: the surface layer is the warmest. Divers and snorkellers going down a few metres often notice a cooler layer, especially early in the season.
• North to south: the northern Adriatic is generally a little cooler than central and southern Dalmatia.
• Rivers and springs: near river mouths and underwater freshwater springs, patches of noticeably colder water are common.

How warm the water feels depends on the person, the air temperature, the wind and the sun. As a rough guide:

• Below about 18°C: bracing. Most people manage a quick dip rather than a long swim.
• About 18 to 21°C: refreshing. Fine for regular swimmers, a shock at first for many others.
• About 22 to 24°C: comfortable for most people, especially on a hot day.
• About 25°C and above: warm. Long swims and snorkelling sessions feel easy.

On a sailing trip, wind and shade on deck make a difference too. Climbing out into a breeze feels much cooler than stepping onto a hot beach, so keep a towel and a layer close by.

In July, August and early September, most guests swim happily without a wetsuit. In May, early June and from October, a thin wetsuit or a long-sleeved rash vest can make longer swims and snorkelling much more pleasant. People who feel the cold, or who plan to spend a long time in the water, may want one even in midsummer.

A rash vest also protects your back and shoulders from the sun while snorkelling, which is often the bigger risk in high summer. Space on a yacht is limited, so pack light kit that folds small. Our packing list covers what fits in a cabin.

Warm, clear water can make the sea look safer than it is. Follow the crew's guidance on when and where to swim, stay away from passing boats and tenders, and never assume conditions are safe because the surface looks calm. Currents and wind can make it harder to swim back to the yacht than it was to swim away. Cold-water shock is possible early and late in the season, so enter gradually if the water feels cold.

Our guide to swimming safely from a yacht covers ladders, buddies and swim lines, and sun and heat at sea explains how to stay comfortable on deck.

For the actual sea temperature before or during your trip, check a current official source. The Croatian Meteorological and Hydrological Service (DHMZ) publishes weather data for the Croatian coast at meteo.hr, including sea temperatures at coastal stations. Readings are taken at fixed points, so the water in a sheltered bay on the day may be a degree or two different.

If you are choosing between dates with swimming in mind, our guide to the best time to sail in Croatia compares the months on weather, crowds and sea conditions.