Last updated: August 1, 2025
Understanding the UV Index is essential for residents and visitors in Sai, Japan, where the climate (Dfb) can lead to varying UV exposure throughout the day. Monitoring these levels not only helps in preventing sunburn but also plays a crucial role in maintaining skin health in the long term. With UV levels peaking at a significant 10 during midday hours, it's important to stay vigilant about sun protection, especially as Sai experiences distinct seasonal shifts. By being aware of the UV Index, you can protect yourself and enjoy the beautiful outdoors safely!
The UV Index throughout the day reflects a dynamic pattern of sun exposure. Starting at 7:00 AM with a low of 3, it gradually climbs to a moderate 4 by 8:00 AM. The real intensity kicks in at 9:00 AM, peaking at 10:00 AM with a maximum UV Index of 8. By 11:00 AM and 12:00 PM, the UV levels rise to 10, indicating high risk for harm from unprotected sun exposure. As the afternoon progresses, the Index begins to decline, with a noticeable drop to 9 at 1:00 PM and further to 7 by 2:00 PM. The sun’s intensity wanes as the day proceeds, plunging to 5 by 3:00 PM, and retreating to 3 at 4:00 PM. By 5:00 PM, the afternoon glow diminishes to 1, where it remains until 7:00 PM, highlighting a day that emphasizes the importance of sun protection during peak hours.
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 2 | low | 45 min |
| 08:00 | 4 | moderate | 30 min |
| 09:00 | 7 | high | 25 min |
| 10:00 | 9 | very high | 15 min |
| 11:00 | 10 | very high | 15 min |
| 12:00 | 11 | extreme | 10 min |
| 13:00 | 10 | very high | 15 min |
| 14:00 | 7 | high | 25 min |
| 15:00 | 5 | moderate | 30 min |
| 16:00 | 3 | moderate | 30 min |
| 17:00 | 1 | low | 45 min |
| 18:00 | 1 | low | 45 min |
| 19:00 | 0 | low | 45 min |
Throughout the year, UV index levels fluctuate significantly, indicating varying risks for sun exposure. January and December see low UV levels (Index 2), with extended burn times of 45 minutes, making sun safety less of a concern. In contrast, April to August marks a critical period with very high to extreme UV levels (Indexes 8 to 11) that dramatically decrease safe burn times to 15 minutes in April to July and just 10 minutes in August. May and June particularly stand out as high-risk months. As summer transitions into early fall, UV levels moderately decline but remain a risk with levels still at 8 in September, requiring continued vigilance. For optimal sun safety, visitors and residents are advised to monitor the UV index, especially during the high-risk months of April to August, adopting protective measures such as sunscreen, clothing, and shade to mitigate 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 |
| Sai | 2 | 3 | 5 | 8 | 9 | 10 | 10 | 11 | 8 | 6 | 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 |