Map from Google - Skyros

The climate of Skyros, the southernmost of the Sporades, is Mediterranean, with relatively mild and rainy winters, and warm and sunny summers. The island is not as warm as the southern Greek islands, it is windy, and in winter is subject to outbreaks of cold air from the Balkan Peninsula.
Here are the average temperatures.
Average temperatures - Skyros
SkyrosJanFebMarAprMayJunJulAugSepOctNovDec
SkyrosJFMAMJJASOND
Min (°F)454546525966707266595448
Max (°F)545557647279828177706357

Precipitation follows a Mediterranean pattern, is more frequent from November to March, and is not abundant, since it does not reach 17 inches per year. In summer, the rains are very rare, and occur in the form of short downpour or thunderstorm. The southern part of the island is less rainy than the northern one, and has a particularly arid landscape.
Here is the average precipitation.
Average precipitation - Skyros
SkyrosJanFebMarAprMayJunJulAugSepOctNovDecYear
SkyrosJFMAMJJASONDY
Prec. (in)32.2210.60.20.20.40.81.42.23.116.9
Days1299752223791380

Winter, from December to mid-March, is not so mild: there are several days with highs below 50 °F, and with a moderate or even strong wind. Furthermore, every so often, it can get very cold and it can even snow, although frosts almost never occur, because of the influence of the sea. The rains are quite frequent. There are also mild periods, with highs around 59/64 degrees.

Snow in Skyros

Spring, from mid-March to May, is a pleasant season, mild and sunny, but some periods can be a bit cold, windy and rainy, although they gradually become less frequent.

Summer, from June to mid-September, is warm and sunny, with very few showers. Generally, the maximum temperature is below 85 °F, and the prevailing wind, coming from the north, makes the temperature almost always acceptable. The Meltemi blows with a certain intensity in periods of a few days, but less than in the Cyclades. Very hot days are rare: occasionally, less than once a year, the temperature can exceed 95 °F, as happened in July 2011, when it reached 98.5 °F, and in July 1988, when it reached 100.5 °F.

Autumn, from mid-September to November, is pleasantly warm at first, then gradually becomes milder. The rains gradually become more frequent, although still in October there are long periods without rain. In November, the first days a bit cold and windy occur, and sometimes even in October.

The amount of sunshine in Skyros is very good in summer, and also in May, when clear skies prevail, while in the rest of the year it's not so remarkable, since there are several periods when the sky it's cloudy.

Skyros

The temperature of the sea, still cold in May, and cool in June, becomes acceptable in June and September, and reaches a peak in August of 75 °F.
Here are the average sea temperatures.
Sea temperature - Skyros
SkyrosJanFebMarAprMayJunJulAugSepOctNovDec
SkyrosJFMAMJJASOND
Sea (°F)595757596470737573706461

When to go

The best time to go to Skyros, for swimming and sunbathing, is summer, from June to mid-September. In June and September, and sometimes in early July, there may be some cool evenings, so it's better to bring a sweatshirt.
In May, not only the sea is cold, but sometimes there can be some cool days, with highs below 68 °F, especially in the first part of the month.
For excursions on the island, to visit the castle or the Byzantine monastery, or to climb Mount Olympus, 1,300 feet high, the summer temperatures are generally acceptable, being not too high, however, you can go even in May.

Back to the Sporades Islands.