How can an archipelago experience a humid continental climate?

Question

Given an archipelago around 40 degrees south latitude, and slightly farther out west than New Zealand from a North-South continent roughly similar to the Americas, how could such an archipelago experience a humid continental climate? Looking at the climate of similar islands on Earth, I see that there aren't seasonal temperature swings, probably because they are beset by water on all side, and experience strong winds year round. Without changing the geography, what could I do to explain the warm summers?

Note that there is an Antarctica analogue, though with another archipelago connecting it to the North-South continent. The other continents are much farther away. The planet is more or less similar to Earth.

Answer 1

If you look at the distribution of climates on Earth, in particular to the one of humid continental climate, you will see that Hokkaido fits the bill for the warm summer subtype.

Hokkaido also happens to be part of an archipelago, the main difference being that it is located around 45 degrees, not 40.

Using the Köppen climate classification, a climate is classified as humid continental when the temperature of the coldest month is below 0 °C [32.0 °F] or −3 °C [26.6 °F] and there must be at least four months whose mean temperatures are at or above 10 °C (50 °F).

Warm summer subtype:

Also known as Hemiboreal climate, areas featuring this subtype of the continental climate have an average temperature in the warmest month below 22 °C (72 °F). Summer high temperatures in this zone typically average between 21–28 °C (70–82 °F) during the daytime and the average temperatures in the coldest month are generally well or far below the −3 °C (27 °F) (or 0 °C (32.0 °F)) isotherm. Frost-free periods typically last 3–5 months. Heat spells lasting over a week are rare. [...] The cool summer subtype is marked by mild summers, long cold winters and less precipitation than the hot summer subtype; however, short periods of extreme heat are not uncommon. Northern Japan has a similar climate.