Map from Google - Lesbos

In Lesbos, island of the eastern Aegean Sea, a short distance from the Turkish coast, the climate is Mediterranean, with mild, rainy winters and hot, sunny summers. The average temperature of January is 9.5 °C (49 °F), that of July is 26 °C (79 °F).
Here are the average temperatures.
Average temperatures - Lesbos
LesbosJanFebMarAprMayJunJulAugSepOctNovDec
LesbosJFMAMJJASOND
Min (°C)77811151922211815129
Max (°C)121315192428303027221714
Min (°F)454546525966727064595448
Max (°F)545559667582868681726357

Precipitation amounts to 670 millimetres (26.5 inches) per year, and is concentrated between November and March; it often occurs in the form of thunderstorm, and sometimes can be abundant. In summer basically it never rains. In the interior of the island there are some hilly areas, culminating in Mount Lepetymnos and Mount Olympos, both more than 900 metres (3,000 feet) high. Some areas of the island are green, while others, particularly in the west, are drier.
Here is the average precipitation.
Average precipitation - Lesbos
LesbosJanFebMarAprMayJunJulAugSepOctNovDecYear
LesbosJFMAMJJASONDY
Prec. (mm)13095754520624104095145670
Prec. (in)5.13.731.80.80.20.10.20.41.63.75.726.4
Days12108641012591270

Winter, from December to mid-March, is quite mild: daytime temperatures hover about 12/13 °C (54/55 °F). The rains are frequent, but there are also sunny days. Cold air from the north can lead to cold periods, with maximum temperatures below 10 °C (50 °F); moreover, the wind can increase the feeling of cold. It can sometimes even snow.

Spring, from mid-March to May, is mild, and over the weeks becomes progressively warmer, and with more sunshine and less rain.

Summer, from June to mid-September, is hot and sunny. The Meltemi, the wind from the north-west, blows from mid-May, cooling the air, but with lower intensity than the in central islands of the Aegean Sea. Periods of intense heat, with highs about 35 °C (95 °F), are quite frequent, and sometimes temperatures can touch 38/40 °C (100/104 °F), but luckily sea breezes blow in the afternoon.

Autumn, from mid-September to November, is often sunny and pleasantly warm at the beginning, and gradually becomes milder, and also wetter.

The amount of sunshine in Lesbos is great in summer, when clear skies prevail, it is very good in spring, while in autumn and winter there are sunny periods, but also others characterized by clouds and rain.

Mytilene

The temperature of the sea in this part of the Aegean Sea is never very high, however it reaches a maximum of 23 °C (73 °F) in July and August.
Here are the average sea temperatures.
Sea temperature - Lesbos
LesbosJanFebMarAprMayJunJulAugSepOctNovDec
LesbosJFMAMJJASOND
Sea (°C)141414151822232322201715
Sea (°F)575757596472737372686359

When to go

The best time to go to Lesbos for beach life runs from June to mid-September. In early June it can still be a little cool in the evening: for safety you can bring a sweatshirt.
In May, not only the sea is still a bit cold, but the air can be cool even for sunbathing, at least on certain days.
To visit the ruins of ancient Greece or the Middle Ages, the best time is spring, in April and May, because in summer it can be hot. You can also choose autumn, at least until October, because later the rains increase.

Back to the North Aegean Islands.