The northern Adriatic is a shallow basin. Shallow water changes temperature faster than deep water — which is why the sea here is cold well into spring and still swimmable when the air has turned.
April and May
The sea is somewhere in the mid-teens in April and creeps towards eighteen or nineteen by late May. That is cold. Children will go in regardless; most adults will get to their knees and think better of it.
What these months are for is everything else. The interior is green, the hill towns are empty, the walking and riding conditions are the best of the year, and the air is in the low twenties. If you are coming for the landscape rather than the water, this is the window.
June
By mid-June the sea is around twenty-two degrees and the swimming season has properly started. The crowds have not arrived, the days are at their longest, and everything is open.
June is the month most people should book and do not. It is warm enough for the beach without being hot enough to make the middle of the day unusable.
July and August
Sea temperature in the mid-twenties, air in the low thirties, everything full. The water is at its best and so is everything else — but this is also when the coastal roads back up, the car parks fill by ten and the popular coves are shoulder to shoulder.
If your dates are fixed by school holidays, this is what you get, and it is still very good. Adjust by going out early and late rather than by fighting the middle of the day.
Where to stay
Apartment Gordana
Where to stay
Villa Karla
September, the best month
The sea in September is warmer than in June — around twenty-three or twenty-four degrees, because the basin has spent the whole summer absorbing heat and gives it back slowly. The air has come down into the high twenties. Most of the crowd has gone home in the last week of August.
Add the start of the grape harvest and the beginning of truffle season in the interior, and September is the single best month to be in Istria. The only thing you lose is an hour of daylight in the evening.
October and after
The sea stays around twenty degrees well into October and hardy swimmers keep going into November. The weather becomes changeable, some seasonal restaurants close, and the interior comes into its own — truffle season is at its peak and the woods turn.
By November the coast is quiet and Istria becomes a place to eat and walk rather than swim. That is a real holiday too, just not the one on the postcard.
What this means for booking
If you can choose your weeks, choose the first half of June or the first half of September. Same sea, half the traffic, and prices that are noticeably lower than the peak.
