Map from Google - Patmos

In Patmos, an island of the Eastern Aegean Sea, and belonging to the Dodecanese group, the climate is Mediterranean, with mild and rainy winters, and warm and sunny summers. The average temperature in January and February is 10 °C (50 °F), while in July and August it's 25 °C (77 °F).
Here are the average temperatures.
Average temperatures - Patmos
PatmosJanFebMarAprMayJunJulAugSepOctNovDec
PatmosJFMAMJJASOND
Min (°C)77811141821211814119
Max (°C)131315192327292926221814
Min (°F)454546525764707064575248
Max (°F)555559667381848479726457

The rains amount to almost 700 millimetres (27.5 inches) per year, and are concentrated between October and April; they often occur in the form of thunderstorm, and sometimes they can be abundant. In summer it almost never rains. Due to the length of the dry period, the landscape is semi-arid.
Here is the average precipitation.
Average precipitation - Patmos
PatmosJanFebMarAprMayJunJulAugSepOctNovDecYear
PatmosJFMAMJJASONDY
Prec. (mm)14095804025953174585145685
Prec. (in)5.53.73.11.610.40.20.10.71.83.35.727
Days12109642102681373

Winter, from December to mid-March, is mild enough: daytime temperatures hover around 13/14 °C (55/57 °F). The rains are quite frequent, and can sometimes be abundant, especially in December and January; however, there's no shortage of sunny days. Sometimes it can be a bit cold, with highs below 10 °C (50 °F), and a cold wind blowing from the north. The wind can increase the feeling of cold. Every now and then, even snow can fall.

Spring, from mid-March to May, is mild, and over the weeks becomes progressively warmer, with more sun and less rain. From mid-May the Meltemi begins to blow, an insistent wind, cool and dry, blowing 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. The Meltemi, the wind from the north-west, often blows, making the temperature generally acceptable, although it blows with less intensity than in the Central Aegean Islands. When the Meltemi blows, the maximum temperature remains below 30 °C (86 °F), otherwise the temperature rises, and there may be periods of intense heat, which usually last a few days, with highs about 33/36 °C (91/97 °F).

Autumn, from mid-September to November, is pleasantly warm and often sunny at first, and gradually becomes milder, while the rains become more frequent.

Patmos, panorama

The amount of sunshine in Patmos is great in summer, when clear skies prevail, it is very good in late spring, while in autumn and winter, sunny periods alternate with others characterized by clouds and rain.
Here are the average sunshine hours per day in nearby Kos.
Sunshine - Kos
KosJanFebMarAprMayJunJulAugSepOctNovDec
KosJFMAMJJASOND
Sun (hours)56791113141311865

The sea is warm enough for swimming from July to September, when it reaches 23 °C (73 °F): we are in the Aegean area, which is not very warm, because of the wind, which mixes the surface waters with the deeper ones.
Here are the average sea temperatures.
Sea temperature - Patmos
PatmosJanFebMarAprMayJunJulAugSepOctNovDec
PatmosJFMAMJJASOND
Sea (°C)161615161821232323211817
Sea (°F)616159616470737373706463

When to go

The best time to go to Patmos for beach life, runs from June to mid-September.
You can bring a sweatshirt for cool evenings, which occur mainly in June, but in windy periods, those who are sensitive to cold may feel a little cool also in July and August.
In May, not only the sea is still a bit cold, but the air too can be cool for sunbathing, at least on certain days.
To visit cities and for excursions and walks, you can choose spring, in April and May, since in summer it can be hot (though quite rarely). You can also choose autumn, at least in September and October, because later the rains increase.

Back to the Dodecanese.