Vitamin D in Japan in May: sun, UV and what to expect
Bad weather Bad weather: it rains on about 21 days in May (rainy or monsoon season), so sun is hard to count on and a beach stay is not recommended.
6.9 hsun window (UV 2.5+)
7.4peak UV Index
7 minto a full dose
27°Cafternoon high
21/30rainy days
22/30sunny days
The country rating is for a typical beach, but some places in Japan still work in May: Zamami (excellent), Naha (excellent).
How long in the sun in May?
- If you travel anyway, plan your sun session around midday (roughly 11:00 to 15:00), when the UV Index peaks at about 7.4. With about a quarter of your skin bare, a full dose takes around 7 minutes for skin type III at age 30, and about 14 minutes at age 65.
- Stop well before your skin turns pink. At this UV level skin type III can start to burn after about 27 minutes of midday sun, so cover up, find shade and use SPF 30+ on skin that stays out.
- On clear days the UV Index reaches about 8.9, which is very strong. Keep sessions short and protect the rest of the day.
- Water, sand and light surfaces reflect UV, so at the beach you get a little more sun than the number suggests, for the good and the bad.
| Skin type | Full dose, age 30 | Full dose, age 65 | Time to burn |
|---|---|---|---|
| Type I | 5 min | 9 min | 18 min |
| Type II | 6 min | 11 min | 23 min |
| Type III | 7 min | 14 min | 27 min |
| Type IV | 11 min | 20 min | 41 min |
| Type V | 14 min | 27 min | 54 min |
| Type VI | 24 min | 45 min | 90 min |
Minutes at midday for about 1,000 IU of vitamin D with a quarter of the body bare, at Miyakojima, the median coastal place. Time to burn is the time to reach one minimal erythemal dose and does not depend on age. A rough planning guide, not medical advice.
Places in Japan in May
| Place | Rating | Sun window | Full dose | Afternoon high | Rainy days |
|---|---|---|---|---|---|
| Zamami | Excellent | 6.9 h | 7 min | 25°C | 15/30 |
| Naha | Excellent | 7.1 h | 8 min | 26°C | 16/30 |
| Miyakojima | Bad weather | 6.9 h | 7 min | 27°C | 21/30 |
| Onna | Bad weather | 6.7 h | 8 min | 26°C | 18/30 |
| Ishigaki | Bad weather | 7.4 h | 7 min | 28°C | 25/30 |
Other months in Japan
- Jan Too cold
- Feb Too cold
- Mar Too cold
- Apr Bad weather
- May Bad weather
- Jun Bad weather
- Jul Bad weather
- Aug Bad weather
- Sep Bad weather
- Oct Bad weather
- Nov Good
- Dec Too cold
Best months: November. Full Japan guide