Map from Google - Cyprus

Cyprus has a Mediterranean climate along the coast, while in the interior plain of Nicosia, the climate is hotter in summer; in the mountainous areas, the climate is obviously colder.
Along the coast, the climate is typically Mediterranean, with an average daily temperature in January of around 11/12 degrees Celsius (52/54 °F). Rainfall is not abundant, about 350/400 millimetres (14/16 inches) per year in cities like Larnaca and Limassol, most of which occurs from November to March, with a peak in December and January. In winter, periods of bad weather, sometimes even a little cold, alternate with periods of good weather, when the sun shines. Summer along the coast is long, since it runs from late May to early October, and it's hot and sunny, a little muggy but also tempered by steady breezes. In general, along the coasts it never rains for a long period, from June to September, during which the sun always shines.
Here are the average temperatures of Larnaca.
Average temperatures - Larnaca
Min (°C)87912162022232017139
Max (°C)171719232730323331282318
Min (°F)464548546168727368635548
Max (°F)636366738186909188827364

As mentioned, the rains on the coast follow a Mediterranean pattern, and are not abundant, although occasionally they can be heavy in the winter. Here the average rainfall in Larnaca.
Here is the average precipitation in Larnaca.
Average precipitation - Larnaca
Prec. (mm)8040352093107155595353

The sea in Cyprus is warm enough for swimming from June to October. In winter, it is a bit cold, but not too much.
Sea temperature - Larnaca
Sea (°C)181717182024262727252219
Sea (°F)646363646875798181777266

In the Mesaoria Plain, the winter weather is still mild, but it's slightly cooler: the average temperature in January is about 9/10 °C (48/50 °F), and at night the temperature can drop around the freezing point. Summer is very hot, so that in the capital Nicosia, the maximum average is about 36 °C (97 °F) in July and August. This inland area makes Cyprus the hottest island of the Mediterranean, while the climate of the coast is similar to that of other Mediterranean islands. The highest temperatures are recorded during heat waves coming from Africa: in Nicosia the temperature may reach or exceed 40 °C (104 °F) from May to October. The rainfall pattern is similar to the coast: in Nicosia the average annual precipitation is about 360 mm (14 in), of which 70 mm (2.8 in) in December and January, while it never rains in summer, during which the sky is almost always clear as on the coast.
Average temperatures - Nicosia
Min (°C)55610151820201814107
Max (°C)141518232832363632272216
Min (°F)414143505964686864575045
Max (°F)575964738290979790817261

The reason why in Nicosia the summer is so hot, relies in the fact that the plain where it is located is locked between two chains of mountains, which hinder the sea breezes to reach the area: in the north lies the chain of Kyrenia (or Girne), while in the south, namely in the central part of the island, lie the Troodos Mountains, culminating in Mount Olympus, 1,952 metres (6,404 feet) high. Here there is also a ski lift for winter sports. The two mountain ranges have a greener landscape and are covered by forests.
Here are the average temperatures of Prodromos, situated at the foot of Mount Olympus, at 1,300 metres (4,250 feet) of altitude.
Average temperatures - Prodromos
Min (°C)114711151919151173
Max (°C)781216212529292520149
Min (°F)343439455259666659524537
Max (°F)454654617077848477685748

Here precipitation amounts to 800 mm (31.5 in) per year, and in winter, when it can also snow and freeze, it is abundant. In summer, rare thundershowers are possible. Here is the average precipitation.
Average precipitation - Prodromos
Prec. (mm)165130805040202525153570150805


When to go

To visit the cities of Cyprus, the Greco-Roman ruins as well as the Byzantine monasteries, the best periods are spring and autumn, and in particular from mid-April to mid-May, and from mid-October to mid-November, when you can find daytime temperatures of around 20/25 °C (68/77 °F), with cool nights, sometimes a bit cold in the plain of Nicosia; sometimes, however, it could rain. Spring is more advisable, because it has longer days, and also because in this period nature is in bloom. These two season are best to avoid the summer heat, and this applies especially for the plain of Nicosia, in which the heat is often intense.
For a beach holiday, you can go from mid-May to mid-October, even though in May the sea is still cool.
It is possible to combine sunbathing with excursions, for example in June and September, remembering that it can get hot, especially away from the coast.

What to pack

In winter: spring/autumn clothes, sweater, jacket, raincoat or umbrella; for the mountains, warm clothes, down jacket, hat.
In summer: light clothing, sunscreen, sun hat, light sweatshirt for the evening, scarf for the breeze; for the mountains, sweatshirt or sweater, light jacket, hiking shoes.