Map from Google - Ustica

Ustica, an island located about 65 kilometres (40 miles) north of Palermo, has a Mediterranean climate: winters are mild and relatively rainy, with sunny periods, but also waves of bad weather, characterized by wind and rain, while summers are hot and sunny, a bit stuffy, but tempered by the breeze. In spring, in April and May, sometimes fog can form in the morning. Although the temperature is generally mild, the wind, which blows especially in the cold half of the year, can increase the sensation of cold.
The island is accessible by boat from Naples and Palermo. In inland areas there are hills, and on the highest point, 250 metres (820 feet) above sea level, lies the weather station: here, the average temperature recorded in January and February is 11 °C (52 °F), that of August 25.5 °C (78 °F). In the plain you can expect temperatures about 1 degree Celsius (1.8 degrees Fahrenheit) higher.
Snow is very rare, and only occurs in the coldest periods. The lowest recorded temperature are around 0 °C (32 °F) in January, February and March, while the highest, which occur when the sirocco blows from Africa, are around 38/39 °C (100/102 °F), from June to August.
Here are the average temperatures.
Average temperatures - Ustica
UsticaJanFebMarAprMayJunJulAugSepOctNovDec
UsticaJFMAMJJASOND
Min (°C)9910111518212220171311
Max (°C)131314162125282926221715
Min (°F)484850525964707268635552
Max (°F)555557617077828479726359

In Ustica, 505 millimetres (20 inches) of rain per year fall, with a maximum in autumn, in October and November, and a minimum in summer, when it hardly ever rains. As you can see in the following table, already in May there is little rain.
Here is the average precipitation.
Average precipitation - Ustica
UsticaJanFebMarAprMayJunJulAugSepOctNovDecYear
UsticaJFMAMJJASONDY
Prec. (mm)50503540201052055757565505
Prec. (in)221.41.60.80.40.20.82.2332.619.9
Days98753111479965

The amount of sunshine in Ustica is excellent in summer, when clear skies prevail; in winter, sunny periods, which can occur in this season as well, alternate with periods in which the sky is cloudy.
Sunshine - Ustica
UsticaJanFebMarAprMayJunJulAugSepOctNovDec
UsticaJFMAMJJASOND
Sun (hours)456791011108654

Ustica from above

The beaches in Ustica are few, since the island is of volcanic origin: generally the coast is formed by cliffs overlooking the sea, or by small bays where you can sunbathe, like the famous Cala Sidoti. Thanks to the Marine Protected Area, in the north-west coast it is possible to swim (and dive) in waters where it is forbidden for any kind of boat to pass.
The sea in Ustica is warm enough for swimming from July to September. In June, the sea is still a bit cool.
Here are the average sea temperatures.
Sea temperature - Ustica
UsticaJanFebMarAprMayJunJulAugSepOctNovDec
UsticaJFMAMJJASOND
Sea (°C)151414151821252625221916
Sea (°F)595757596470777977726661

When to go

The best time to go to Ustica for a beach holiday, is the summer, from June to August. For swimming, the best time is from July to September, but in September, which overall is still a good month (especially in the first half), the first weather disturbances begin to pass. In June, as mentioned the sea is still a little cool, while in May it is still cold, and sometimes the air can be a little too cool for sunbathing as well (perhaps because of the wind).

April and May are advisable for hiking, perhaps in the prehistoric village, while in summer it can sometimes be hot to get around (especially in July and August: in June and September usually the temperature is enjoyable or at least tolerable). In October, the temperatures are mild, but the days are shorter and the weather can be rainy and windy.

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