Weather in Sendai in December

The month to avoid. Of the twelve, December is the one to avoid. Highs sit at 5.1 °C and the day is short; this is an indoors-with-excursions month, not an outdoors-all-day one.

December ranks 10 of 12 — near the bottom of Sendai's year. May is the month that works, and the swing between the two is 68 points, which is a different holiday rather than a slightly better one.

Rain on 23 of the month's 31 days, 4 of them heavy. At that frequency a wet-weather backup is not a contingency, it is the itinerary — book the indoor things first and treat the clear days as the bonus. Layers, and a genuinely waterproof outer — at 5.1 °C the difference between a good day and a miserable one is entirely down to what you are wearing.

What the averages hide

Averages flatten a month, and this one hides a few things: 20 nights drop below freezing, so anything left outside stays frozen; the day barely swings — 5.7 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest December day reached 20 °C and the coldest night fell to -9.2 °C, and the wettest single day dropped 76 mm — roughly 51% of the month's rain in one day.

December is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest December on record still delivered 290 mm against 56 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 150 mm average is a reasonable planning figure, not a promise.

Wind is light at 4.8 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 93%, which at 5.1 °C means damp rather than muggy — the kind of cold that gets into a coat and stays there.

How December sits in the year

The month is on the way down: 7.2 °C cooler than November, with January dropping another 3.4 °C. The first week and the last are not the same trip.

Daylight in December

December sits at the dark end of Sendai's year — 9.5 hours of daylight against 14.8 at midsummer, holding steady all month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

Sea temperature

The sea sits at about 14.9 °C in December — cold — a quick dip rather than a swim, and a wetsuit if you are in for longer. The sea peaks at 23.9 °C in August and bottoms out at 10 °C — water lags the air by a month or two, which is why the best swimming often comes after the best weather.

How busy it gets

Quiet. Few other visitors, cheaper rooms, and a real chance some seasonal operators are shut.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

December in Sendai versus nearby

If Sendai is one option among several, the nearby comparison is worth making. Niigata is a better bet in December — 4.2 °C warmer, 2 days more rain. Utsunomiya is a better bet in December — 4.3 °C warmer, 17 days less rain.

So: December is a compromise. May is 61 points better and is what Sendai is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Sendai

See all twelve months in Sendai, or where else to go in December.