Majorca, where it is

The climate of Majorca (or Mallorca), the largest of the Balearic Islands, is Mediterranean, with mild winters and hot and sunny summers, which are a bit sultry but tempered by sea breezes. The average temperature ranges from 9.5 °C (49 °F) in January and February to 24.5 °C (76 °F) in August.
Here are the average temperatures in Palma, the largest city.
Palma - Average temperatures
Min (°C)445711151718161285
Max (°C)151617192327313128231916
Min (°F)393941455259636461544641
Max (°F)596163667381888882736661

Rainfall, at least in the plains, is not abundant, since it amounts to about 400 millimeters (16 inches) per year, and follows the Mediterranean pattern, so it's more common in autumn and winter, and decreases gradually during spring, reaching a minimum in summer, when it almost never rains.
Here is the average precipitation.
Palma - Average precipitation

Owing to the wind that blows from France, Majorca is windy enough, especially from October to April. In summer, sea breezes blow, but they are welcome because they make the heat more bearable.

Sierra de Tramontana and sea

In the northern part, the island is occupied by a mountain range, called Sierra de Tramontana, whose highest peak is Puig Major, 1,445 meters (4,741 feet) high. These mountains, which overlook the sea, have a colder climate because of altitude, and in winter can be covered with snow; in addition, they are more windy (the north wind is felt in a particular way) and receive higher precipitation, up to 1,200 mm (47 in) per year, so they are also greener, and not by accident they are covered by forests.

South of Mallorca we find the small archipelago of Cabrera, made up of small islands and islets, protected in the national maritime-terrestrial park of the same name.

Winter, from December to February, is mild, with many sunny days, but also with periods of rain and wind. On clear nights, it can get quite cold, and the temperature can approach the freezing point. Sometimes there can be cold and windy days, with highs below 10 °C (50 °F), which can be followed by light frosts, with lows a few degrees below freezing.

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

The amount of sunshine in Majorca is not very good in winter, when Atlantic or Mediterranean depressions can affect the island, however, there is a moderate amount of sunny days even in this period. Spring is a sunny season, especially in May. The sunniest period is from June to August, when sunny days are the norm. In September, the first Atlantic disturbances can reach the island, so in autumn the sun is not always guaranteed.
Palma - Sunshine

Cathedral, sea in the background

The sea in Majorca is warm enough for swimming from July to September, while in June and October it is quite cool. Here are the average sea temperatures.
Majorca - Sea temperature
Temp (°C)141414151721242624221816
Temp (°F)575757596370757975726461

Best Time

The best time to visit Majorca for a beach holiday is the 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. June is a sunny month, but the sea is still a bit cool; in May, the sea is cold, and sometimes the air can be a bit cold as well, especially in the first half of the month.

April and May are suitable to visit the island and its cities; summer is the best season for hiking in the mountains, while sometimes it can be too hot for hiking and visiting the cities of the plain. In October, the temperatures are mild, but the days are shorter and the weather can be rainy and windy.