Last updated: August 1, 2025
In Koshi, Japan, staying informed about the UV Index is vital for safeguarding your skin against the sun's harmful rays. Understanding UV levels is essential not only for preventing painful sunburns but also for promoting long-term skin health. With a humid subtropical climate (Cfa) often yielding high UV exposure, particularly during midday hours (with peak indices reaching 12), being aware of the UV Index can help you take necessary precautions. Whether you’re enjoying outdoor activities or simply relaxing in the sun, knowing how to protect yourself from UV radiation is crucial for maintaining your well-being in Koshi’s vibrant environment.
The UV Index for the day reveals a dynamic shift in sun exposure, peaking dramatically between 11:00 AM and 1:00 PM. Starting the morning with a mild maximum of 2 at 7:00 AM, the index steadily rises, reaching 12 by midday—an indication of high risk for harm from unprotected sun exposure. As the afternoon progresses, it dips to 10 at 2:00 PM and then gradually decreases to a more moderate level of 4 by 4:00 PM. By the evening, the UV Index settles back down to 1 by 6:00 PM, signaling a safe time to enjoy the outdoors again. Be sure to protect your skin during those peak hours!
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 1 | low | 45 min |
| 08:00 | 3 | moderate | 30 min |
| 09:00 | 5 | moderate | 30 min |
| 10:00 | 8 | very high | 15 min |
| 11:00 | 11 | extreme | 10 min |
| 12:00 | 12 | extreme | 10 min |
| 13:00 | 11 | extreme | 10 min |
| 14:00 | 10 | very high | 15 min |
| 15:00 | 7 | high | 25 min |
| 16:00 | 4 | moderate | 30 min |
| 17:00 | 2 | low | 45 min |
| 18:00 | 1 | low | 45 min |
| 19:00 | 1 | low | 45 min |
Throughout the year, the UV Index exhibits significant seasonal variations, with spring and summer months posing the highest risk of UV exposure. From March to September, the index reaches very high to extreme levels—particularly during April to August, where it peaks at 12 in July and August. During these months, the burn time shortens dramatically to just 10 minutes, indicating a critical need for sun protection. Conversely, January and December record the lowest UV levels with a moderate exposure category, allowing for more extended exposure times of 30 minutes. Visitors and residents are advised to take precautions, especially from March to September, by wearing protective clothing, applying sunscreen, and seeking shade during peak hours to minimize the risks associated with high UV exposure.
UV Risk Categories
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sapporo UVI | 2 | 3 | 6 | 7 | 9 | 9 | 9 | 10 | 8 | 5 | 3 | 2 |
| Yokohama UVI | 3 | 5 | 8 | 9 | 11 | 11 | 11 | 11 | 10 | 7 | 5 | 4 |
| Tokyo UVI | 3 | 5 | 8 | 9 | 11 | 11 | 11 | 11 | 10 | 7 | 5 | 4 |
| Nagoya UVI | 4 | 6 | 8 | 10 | 11 | 11 | 11 | 11 | 10 | 7 | 5 | 3 |
| Osaka UVI | 4 | 6 | 8 | 11 | 11 | 11 | 12 | 11 | 10 | 7 | 5 | 3 |
| Koshi | 4 | 6 | 8 | 11 | 11 | 11 | 12 | 12 | 11 | 8 | 6 | 4 |