Map from Google - Syros

In Syros, small Greek island belonging to the archipelago of the Cyclades, the climate is Mediterranean, with mild and rainy winters, and warm and sunny summers. The average temperature of January is 10.5 °C (51 °F), that of July is 25 °C (77 °F).
Here are the average temperatures.
Average temperatures - Syros
SyrosJanFebMarAprMayJunJulAugSepOctNovDec
SyrosJFMAMJJASOND
Min (°C)889121519222219161310
Max (°C)131315182226282725211815
Min (°F)464648545966727266615550
Max (°F)555559647279828177706459

The island is windy: in autumn and winter the wind blows during the passage of depressions, the mild ones from the south preceding the Atlantic disturbances, and the ones coming from the northwest associated with cold outbreaks from the Balkan Peninsula, while in summer the Meltemi dominates (see below).
The rains follow a Mediterranean pattern, being concentrated from October to March, and are not abundant, since they amount to 475 millimetres (18.5 inches) per year, and this is confirmed by the landscape, which is arid.
Here is the average precipitation.
Average precipitation - Syros
SyrosJanFebMarAprMayJunJulAugSepOctNovDecYear
SyrosJFMAMJJASONDY
Prec. (mm)906555251552212506590475
Prec. (in)3.52.62.210.60.20.10.10.522.63.518.7
Days1087532002571059

Winter, from December to mid-March, is mild, rainy and windy. The wind, frequent and sometimes stormy, heightens the feeling of cold. There's no shortage of mild days, with highs around 16/18 °C (61/64 °F), but the island is located quite to the north and close enough to the mainland, to receive cold air with some frequency, to the point that there can be cold days, with highs below 10 °C (50 °F), and occasionally even snow can fall.

Snow in Syros, Miaouli square, Ermoupoli

Spring, from mid-March to May, is mild and sunny, but it is often windy. From mid-May the Meltemi starts to blow, an insistent wind, cool and dry, blowing from the north for some days in a row, especially during the day, but sometimes even at night.

Summer, from June to mid-September, is warm and sunny, but also windy. The Meltemi blows for long periods, especially in July and August, and is stronger in the afternoon, but can insist also in the evening. With this wind, the maximum temperature usually remains below or around 30 °C (86 °F), and even in the hottest periods, when in other parts of Greece the temperature touches or exceeds 40 °C (104 °F), here it stops at 35/36 °C (95/97 °F).

Autumn, from mid-September to November, is initially warm and sunny, and gradually becomes cooler and rainy. Even autumn is windy: as long as the weather is good, the Meltemi still blows, while later the wind blows along with autumn disturbances.

The amount of sunshine in Syros is great in summer, when clear skies prevail, while it is not much from November to February, when the sky is often cloudy, even though sunny days can present themselves also in midwinter.

Syros

The temperature of the Aegean Sea is never very high, because the wind that blows in summer tends to keep it a bit low, however it reaches a maximum of 23 °C (73 °F) in July and September and 24 °C (75 °F) in August; in June it's still a bit cool, about 21 °C (70 °F).
Here are the average sea temperatures.
Sea temperature - Syros
SyrosJanFebMarAprMayJunJulAugSepOctNovDec
SyrosJFMAMJJASOND
Sea (°C)151515161821232423211817
Sea (°F)595959616470737573706463

When to go

The best time to go to Syros for beach life is the summer, from June to mid-September. In June, as we said, the sea is cooler than in midsummer.
It's better to bring a sweatshirt for the cool evenings, which occur mainly in June, but given the intensity of the wind, those who are sensitive to cold can feel a little cool even in July and August, and thus can equip themselves also in these months.
To visit the towns and go hiking and walking, spring is fine, in April and May, but since it is normally not too hot, you can usually walk around the island also in summer, except in the rare hot and not windy days.

Back to the Cyclades Islands.