Sea temperature in Japan
Live water temperatures and swimming conditions across 33 beaches on the Japan coast.
Best time to swim in Japan
The sea in Japan peaks in July, when the water averages around 28°C.
The main swimming season runs from April – November, when surface temperatures stay comfortable for extended sessions.
On average, 8 months a year sit above 20°C — the threshold most swimmers describe as pleasant without a wetsuit.
Shoulder months like March and December are noticeably cooler but often quieter, with fewer crowds and steadier weather.
The coldest month is typically January at around 18°C, when cold-water swimmers dominate the coast.
Japan sea temperature history
Long-term climatology for Japan shows an annual mean sea temperature of 23°C, ranging from 18°C in winter to 28°C at the summer peak.
The seasonal swing is roughly 10°C between the coldest and warmest month — a useful yardstick when comparing years or checking whether the current sea is running above or below average.
Recent decades have trended slightly warmer at Japan, in line with regional sea-surface temperature records for the wider basin.
Monthly averages below are drawn from multi-decadal climatology and are updated as new observations arrive.
Values are area averages; individual beaches vary by exposure and depth.
Japan sea temperature: frequently asked questions
What is the warmest month to swim in Japan?
July is the warmest month in Japan, when the sea averages about 28°C. Late-season warmth often persists a few weeks after peak.
When is the sea coldest in Japan?
The coldest month in Japan is typically January, when the water averages around 18°C. Cold-water swimmers and surfers dominate this period.
When can you swim in Japan without a wetsuit?
The main swimming season in Japan runs from April – November — about 8 months a year when the sea sits above 20°C, the level most swimmers describe as pleasant without a wetsuit.
Do I need a wetsuit in Japan?
Outside peak summer the water in Japan drops toward 19°C, so a 3/2mm shorty or full wetsuit makes long swims much more comfortable. In peak months most swimmers go without.
What is the average sea temperature in Japan?
The long-term annual mean sea temperature in Japan is about 23°C, based on multi-decadal climatology of the surrounding waters.
How do I check the current sea temperature in Japan?
The live reading at the top of this page shows the current sea temperature in Japan, updated hourly from marine buoy and satellite data. The 7-day forecast covers water, air, waves, wind and UV for the week ahead.
Japan sea temperature by month
Average sea temperatures around Japan for every month of the year, based on long-term Open-Meteo marine climatology.
| Month | Average sea | Swimming comfort |
|---|---|---|
| January | 18.0°C | Swimmable, refreshing |
| February | 18.0°C | Swimmable, refreshing |
| March | 19.0°C | Swimmable, refreshing |
| April | 21.0°C | Pleasant swimming |
| May | 23.0°C | Pleasant swimming |
| June | 26.0°C | Warm swimming |
| July ⭐ | 28.0°C | Very warm, bath-like |
| August | 28.0°C | Very warm, bath-like |
| September | 27.0°C | Very warm, bath-like |
| October | 24.0°C | Warm swimming |
| November | 21.0°C | Pleasant swimming |
| December | 19.0°C | Swimmable, refreshing |
Monthly figures are modelled climatology averages, not live readings. How accurate is our data?
Warmest beaches in Japan right now
| Beach | Region | Sea | Swim score |
|---|---|---|---|
| Yonaha Maehama | Okinawa | 28.3°C | Excellent |
| Nishihama Beach | Okinawa | 28.2°C | Excellent |
| Sunayama Beach | Okinawa | 28.2°C | Excellent |
| Shirahama Beach | Wakayama | 27.5°C | Excellent |
| Naminoue Beach | Okinawa | 27.4°C | Excellent |
| Yumigahama Beach | Shizuoka | 27.4°C | Excellent |
| Nirai Beach | Okinawa | 27.3°C | Excellent |
| Emerald Beach | Okinawa | 27.2°C | Excellent |
| Araha Beach | Okinawa | 27.2°C | Excellent |
| Katsurahama Beach | Kochi | 27.1°C | Excellent |
| Ibusuki Beach | Kagoshima | 27.1°C | Excellent |
| Suma Beach | Hyogo | 27.1°C | Excellent |
| Furuzamami Beach | Okinawa | 27.0°C | Excellent |
| Nigishima Beach | Mie | 27.0°C | Excellent |
| Iritahama Beach | Shizuoka | 27.0°C | Excellent |
| Sunset Beach Naha | Okinawa | 26.8°C | Excellent |
| Manza Beach | Okinawa | 26.8°C | Excellent |
| Sunset Beach Chatan | Okinawa | 26.7°C | Excellent |
| Sotoura Beach | Shizuoka | 26.7°C | Excellent |
| Aoshima Beach | Miyazaki | 26.6°C | Excellent |
| Shirahama Beach Izu | Shizuoka | 26.6°C | Excellent |
| Mibaru Beach | Okinawa | 26.4°C | Excellent |
| Kabira Bay | Okinawa | 23.4°C | Excellent |
| Kondoi Beach | Okinawa | 23.3°C | Excellent |
| Onjuku Beach | Chiba | 22.7°C | Excellent |
| Sunayama Beach | Okinawa | 22.6°C | Excellent |
| Kujukuri Beach | Chiba | 22.6°C | Excellent |
| Katsuura Chuo Beach | Chiba | 22.3°C | Excellent |
| Yuigahama Beach | Kanagawa | 22.2°C | Excellent |
| Kujukuri Beach | Chiba | 22.2°C | Excellent |
| Zushi Beach | Kanagawa | 21.7°C | Excellent |
| Zaimokuza Beach | Kanagawa | 21.7°C | Excellent |
| Enoshima Beach | Kanagawa | 21.4°C | Excellent |
Sea temperature in Japan — FAQ
How warm is the sea in Japan in September?
The sea off Japan averages about 27.0°C in September, based on long-term monthly averages for this coast.
When is the best time to swim in Japan?
Japan is warmest in July (around 28.0°C) and coldest in January (around 18.0°C). There are typically 6 months a year when the water sits above 22°C.
What is the average yearly sea temperature in Japan?
Across all twelve months, the sea in Japan averages about 22.7°C.
Do you need a wetsuit to swim in Japan?
In peak season (around July, ~28.0°C) most swimmers are comfortable without a wetsuit. Outside summer, when the water drops toward 18.0°C, a 3/2mm to 5/4mm wetsuit is recommended.
Which beach in Japan has the warmest sea right now?
Nishihama Beach typically has the warmest sea in September, while Yuigahama Beach is the coolest of the featured beaches. Live readings for every beach are listed on this page.