Zakynthos, where it is

The climate of Zakynthos (or Zante), Greek island of the Ionian Sea, is Mediterranean, with mild and rainy winters, and hot and sunny summers.
Here are the average temperatures.
Zakynthos - Average temperatures
Min (°C)889111418202119161210
Max (°C)141416192328313128231916
Min (°F)464648525764687066615450
Max (°F)575761667382888882736661

The rains are quite abundant, given that they amount to nearly 1,000 millimetres (40 inches) per year, but they are concentrated in the period from October to March, while in May and September it rains little, and from June to August it almost never rains.
Here is the average precipitation.
Zakynthos - Average precipitation

Winter, from December to mid-March, is mild but rainy, especially in December and January, when more than 150 millimetres (6 inches) of rain fall per month. However, there is a moderate amount of sunny days. The island is sheltered from cold spells, so that it never snows on the plains, while in inland hills, which reach 758 metres (2,487 ft) above sea level, sometimes it can snow, as happened in February 2012. Sometimes, however, a cold wind from the north can blow, and in the winter months the minimum temperature in the plains can drop to 0 °C (32 °F).

Spring, from mid-March to May, is mild; the rains gradually become rarer, and sunny days become increasingly more frequent. May is a pleasant month, before the summer heat.

Summer, from June to mid-September, is sunny and hot: the maximum temperature often exceeds 30 °C (86 °F), and can easily reach as high as 35 °C (95 °F), especially in August; in the worst moments it can reach 40 °C (104 °F), as happened in August 2006. Luckily, sea breezes blow, providing relief, at least when the heat is not excessive, and in any case you can cool yourself down in the sea. This part of Greece, overlooking the Ionian Sea, is outside the area where the annoying but cooling wind called Meltemi blows, so the sea is warmer as well.

Autumn, from mid-September to November, is mild (initially even warm enough) and rainy. In October, there may still be many sunny days.

Zakynthos, sea and coast

The amount of sunshine in Zakynthos is great in summer, when clear skies prevail, but it is also good in spring, when days with clear skies are already frequent. In contrast, From November to February, sunny days alternate with periods of bad weather.
Zakynthos - Sunshine

The temperature of the sea, which as mentioned is higher than in the Aegean Sea, is warm enough for swimming from July to September, while in June and October it's around 22 °C (72 °F), so it's a bit cool. Here are the average sea temperatures.
Zakynthos - Sea temperature
Temp (°C)161515161822242625222017
Temp (°F)615959616472757977726863

When to go

The best time to go to Zakynthos, for swimming and sunbathing, runs from June to mid-September.
The turtles Caretta caretta arrive on the beaches to lay their eggs in June.
For excursions on the island, the month of May is preferable, or maybe the first half of October, to avoid the summer heat.

Back to the Ionian Islands.