Map from Google - Ulleungdo

In Ulleung-do, an island in the Sea of Japan, about 130 km (80 mi) east of the Korean coast, the climate is temperate humid, with cold and damp winters, warm and sultry summers, and no dry season.
The island has no airport, so it can only be reached by ferry.
In winter, cold winds coming from the Asian continent pick up moisture when passing over the sea, so the island is subject to frequent falls of rain and snow. There can be very cold periods, with highs around freezing (0 °C or 32 °F) and lows dropping down to -6/-8 °C (18/21 °F), and relatively mild periods, with highs around 10/12 °C (50/54 °F), more likely in December. Wind and humidity, however, exacerbate the feeling of cold. In the interior of the island there is a small mountain, Seonginbong, 984 metres (3,228 feet) high, where winter snowfalls are even more copious.
In summer, there are periods of good weather, hot and muggy, with highs around 30/32 °C (86/90 °F), though tempered by the breeze, but also with periods of bad weather, with wind and rain, and sometimes (especially in June and the first half of July), temperatures a bit cool.
Here are the average temperature; the weather station is at 220 metres (720 feet), so on the coast we can expect a temperature roughly 1.5 degrees Celsius (2.7 °F) higher.
Average temperatures - Ulleungdo
UlleungdoJanFebMarAprMayJunJulAugSepOctNovDec
UlleungdoJFMAMJJASOND
Min (°C)-102812162021171372
Max (°C)45915192225272319138
Min (°F)303236465461687063554536
Max (°F)394148596672778173665546

Precipitation is fairly abundant, given that it reaches 1,400 millimetres (55 inches) per year; the wettest period is from July to September, because of the summer monsoon, but winter is the season in which precipitation is more frequent. Here is the average precipitation.
Average precipitation - Ulleungdo
UlleungdoJanFebMarAprMayJunJulAugSepOctNovDecYear
UlleungdoJFMAMJJASONDY
Prec. (mm)115807080105115170170170851051151380
Prec. (in)4.53.12.83.14.14.56.76.76.73.34.14.554.3
Days18151289912121091217143

From August to early October (more rarely in July), Ulleung-do can be affected by typhoons, tropical cyclones of Southeast Asia, which bring strong winds and heavy rains.
The amount of sunshine in Ulleung-do is scarce in winter, when the skies are usually cloudy; in the other seasons it is never very good, however, the sun shines for half of the time during the months of April, May and October, while in summer the sunshine amount decreases again, because of the summer monsoon.

Ulleungdo

In Ulleung-do, the sea becomes warm enough for swimming in August, while it is a bit cool in July and September.
Sea temperature - Ulleungdo
UlleungdoJanFebMarAprMayJunJulAugSepOctNovDec
UlleungdoJFMAMJJASOND
Sea (°C)121010121519222422201612
Sea (°F)545050545966727572686154

About 90 km (55 mi) east-southeast of the island, and visible from the east coast or from the highlands of the interior, we find the Liancourt Rocks (Dokdo in Korean, Takeshima in Japanese), small islands, having a similar climate, just slightly milder and less rainy: the average annual precipitation is around 1,250 mm (49 in).