Last updated: May 3, 2025
Understanding the UV Index is crucial for residents of Seiyo, Japan, as it plays a significant role in protecting skin health and preventing sunburn. With the city experiencing a Cfa climate, sun exposure can vary dramatically throughout the day, reaching peak UV levels of 12 during midday. This makes it essential to be aware of UV levels, especially between 10 AM and 2 PM, when the sun's rays are at their strongest. By staying informed about the UV Index, you can take proactive measures to safeguard your skin and enjoy outdoor activities without compromising your health.
The UV Index presents a striking profile throughout the day, peaking dramatically from 11:00 AM to 12:00 PM with a maximum value of 12, indicating an intense level of solar radiation. Early risers will notice a more moderate ascent as the index starts at 2 at 07:00 AM, gradually climbing to 3 by 08:00 AM. The real intensity begins at 09:00 AM, surging to 6 before reaching a zenith of 11 by 11:00 AM. As the sun begins to dip post-noon, the index recedes to 9 at 02:00 PM, then gently descends to 6 by 03:00 PM, and continues its downward trend to settle at 0 by 07:00 PM. This data emphasizes the importance of sun protection during the peak hours when ultraviolet radiation is most potent.
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 2 | low | 45 min |
| 08:00 | 3 | moderate | 30 min |
| 09:00 | 6 | high | 25 min |
| 10:00 | 9 | very high | 15 min |
| 11:00 | 11 | extreme | 10 min |
| 12:00 | 12 | extreme | 10 min |
| 13:00 | 11 | extreme | 10 min |
| 14:00 | 9 | very high | 15 min |
| 15:00 | 6 | high | 25 min |
| 16:00 | 3 | moderate | 30 min |
| 17:00 | 2 | low | 45 min |
| 18:00 | 1 | low | 45 min |
| 19:00 | 0 | low | 45 min |
The UV Index shows significant seasonal changes, with the highest levels of ultraviolet radiation occurring from March to September, characterized by very high to extreme exposure categories. March and April see UV Index values ranging from 9 to 10, while May through August peak at 12, indicating an extreme risk of harm from unprotected sun exposure, with a notably short burn time of just 10 minutes. July and August are particularly high-risk months, necessitating careful sun protection measures. As the months progress toward October, there is a decrease to 8, moving back to very high levels, while November and December return to high and moderate levels, respectively. To ensure safety, visitors and residents are strongly advised to adopt protective measures, such as using sunscreen, wearing protective clothing, and seeking shade during peak sun hours, particularly during the high-risk months of May through September.
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 |
| Seiyo | 4 | 6 | 9 | 10 | 12 | 11 | 12 | 12 | 11 | 8 | 6 | 4 |