The Dodecanese Islands (also called Southern Sporades) are located in the southeastern part of the Aegean Sea, and have a Mediterranean climate, with mild and rainy winters, and hot and sunny summers.
The main islands of the archipelago are: Agathonisi (or Gaidaro), Astypalaia (or Stampalia), Kalymnos, Karpathos, Kasos, Kastellorizo (or Megisti), Kos, Leipsoi (or Lisso), Leros, Nisyros, Patmos, Rhodes (the largest and most important), Symi, Tilos, and Halki (or Chalki).
Then there are many smaller islands and islets, among which we can mention Pserimos (or Cappari), Farmakonisi, Telendos, Arkoi, Saria, Gyali, Levitha, Ro, Strongyli Megistis, Alimia, Syrna.

Lying in the eastern Aegean Sea, in summer the islands are warmer than the Cyclades, because they are affected on a less intense and continuous manner by the Meltemi, the northerly wind that blows in summer in the central Aegean, except the westernmost islands, such as Astypalaia, which have a climate similar to the Cyclades.
The Dodecanese Islands tend to be milder in winter as well, compared with the Cyclades, in particular they are less susceptible to cold air outbreaks from the continent, since the northwest wind has to cover a longer stretch of sea, so snowfalls in the Dodecanese Islands are very rare, and in practice snow never accumulates on the ground, at least in the plains. However, sometimes it can be a bit cold, so that lows can drop to around 3/5 °C (37/41 °F), and highs to around 7/10 °C (45/50 °F), besides the wind can increase the feeling of cold.
Here for example, the average temperatures of Kalymnos.
Average temperatures - Kalymnos

Kalymnos	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Kalymnos	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	8	7	10	12	15	19	21	21	20	16	12	10
Max (°C)	13	12	15	18	22	27	30	29	27	22	17	13
Min (°F)	46	45	50	54	59	66	70	70	68	61	54	50
Max (°F)	55	54	59	64	72	81	86	84	81	72	63	55

Precipitation in the Dodecanese Islands hovers normally between 650 and 750 millimetres (25 to 30 inches) per year, and is concentrated in the cold period, from October to March, when it can occur in the form of shower or thunderstorm, and can sometimes be abundant.
Because of the long summer drought, the landscape is typically semi-arid, especially in the flat islands and at low altitude (in some islands there are hilly and mountainous areas, which are greener).
This is for example the average rainfall in Rhodes.
Average precipitation - Rhodes

Rhodes	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Rhodes	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	150	120	75	25	15	3	0	0	7	65	90	145	695
Prec. (in)	5.9	4.7	3	1	0.6	0.1	0	0	0.3	2.6	3.5	5.7	27.4
Days	11	9	7	3	2	0	0	0	1	5	6	11	55

The amount of sunshine in the Dodecanese is great in summer, when clear skies are the norm. In winter, periods of bad weather, with cloudy skies, alternate with sunny periods.
Here are the average daily sunshine hours in Rhodes.
Sunshine - Rhodes

Rhodes	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Rhodes	J	F	M	A	M	J	J	A	S	O	N	D
Sun (hours)	5	6	7	9	11	13	14	13	11	8	6	5

The temperature of the sea in summer remains somewhat lower in the central and northern part of the archipelago, as it does not exceed 23/24 °C (73/75 °F) in July and August, while it becomes higher in the southern islands, such as Karpathos, Rhodes and Kastelorizo, where it can reach 25/26 °C (77/79 °F).
Here, for example, the temperature of the sea in Kos.
Sea temperature - Kos

Kos	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Kos	J	F	M	A	M	J	J	A	S	O	N	D
Sea (°C)	17	16	16	17	19	22	23	24	24	22	19	17
Sea (°F)	63	61	61	63	66	72	73	75	75	72	66	63

The best time to go to the Dodecanese islands for a beach holiday is the summer, from June to mid-September. In early June, it can be a little cool in the evening: for safety you can bring a sweatshirt. Especially in the western islands, you can bring a light sweatshirt for windy evenings also in midsummer.
In May, not only the sea is still a bit cold, but the air can also be cool for sunbathing, at least on certain days.
To visit the ruins of ancient Greece or the cities, or for excursions to the interior of the islands, you can choose spring, in April and May, since in summer it can be very hot. You can also choose autumn, at least in the first half of October, because later the rains increase.

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