Minorca, where it is

The climate of Minorca (or Menorca), the north-easternmost of the Balearic Islands, is Mediterranean, with mild, relatively rainy winters and hot, sunny summers, which are a bit sultry but tempered by sea breezes. The average temperature ranges from 11 °C (52 °F) in January and February to 25 °C (77 °F) in August.
Here are the average temperatures at the Mahón Airport.
Minorca - Average temperatures
Min (°C)88810131720211915119
Max (°C)141416172125282926221815
Min (°F)464646505563687066595248
Max (°F)575761637077828479726459

Rainfall amounts to about 600 millimeters (23.5 in) per year, and follows the Mediterranean pattern, so it's more common in autumn and winter, and gradually decreases during spring, reaching a minimum in summer, when it seldom rains. Menorca is the rainiest of the Balearics, although generally the difference is noticeable especially in autumn, when sometimes the rains are abundant.
Here is the average precipitation.
Minorca - Average precipitation

Owing to the north wind that blows from France, Minorca is pretty windy, especially from October to April. Actually, sindce it lies directly to the south of the Gulf of Lion, it is the windiest of the Balearic Islands. On the other hand, in summer, sea breezes blow, but they are welcome because they make the heat more bearable.

Winter, from December to February, is mild, with many sunny days, but also with periods of rain and wind. The weather is rarely very cold, however, sometimes there can be cold and windy days, with highs below 10 °C (50 °F), which can be followed by cold nights, with lows around freezing (0 °C or 32 °F).

Summer, from June to mid-September, is typically Mediterranean, that is, hot and sunny, with rare thundershowers. At times there can be some heat waves in July or August, with highs about 35/38 °C (95/100 °F).

The amount of sunshine in Menorca is not very good in winter, when Atlantic or Mediterranean depressions pass quite often, however, there is a moderate amount of sunny days also in this period. Spring is a sunny season, especially in May; the sunniest period is from June to August, when clear skies are the norm. In September, the first Atlantic disturbances occur, so in autumn the sun is not always guaranteed.
Minorca - Sunshine

Beach in Minorca

The sea in Menorca is warm enough for swimming from July to September, when it reaches or exceeds 24 °C (75 °F), while in June and October it is quite cool. Here are the average sea temperatures.
Minorca - Sea temperature
Temp (°C)151414151721242524221916
Temp (°F)595757596370757775726661

Best Time

The best time to visit Menorca for a beach holiday is summer, from June to mid-September. The water temperature is comfortable enough from July to September, although in September, which overall is still a good month (especially in the first half), the first periods of bad weather may occur. May and June are sunny months, but the sea is still a bit cool, especially in May, when it is actually cold, and sometimes cold and windy days can still occur.

April and May are suitable to visit the island and its cities, while in summer it can sometimes be hot for hiking, especially in July and August. In October and November, the temperatures are mild, but the days are shorter and the weather can be rainy and windy.