Last updated: June 2, 2025
Understanding the UV Index is crucial for residents and visitors of Hachijo, Japan, where the unique Cfa climate creates distinct sun exposure patterns. As UV levels can peak significantly—reaching a maximum of 12 around midday—awareness is key to preventing sunburn and protecting skin health. With UV exposure risks heightened during the summer months, knowing when to seek shade or apply sunscreen can make all the difference. Each day on Hachijo offers a variety of UV conditions, making it essential to stay informed and prepared for outdoor activities.
The UV Index for the day shows a dynamic range of intensity as the sun rises higher in the sky. Starting at 3 by 7:00 AM, the index climbs steadily to 5 at 8:00 AM, then surges to 7 by 9:00 AM. The peak arrives around 11:00 AM and 12:00 PM, hitting a high of 12, indicating a significant risk for harm from unprotected sun exposure. As the afternoon progresses, the index begins to wane, dropping to 11 at 1:00 PM and down to 8 by 2:00 PM. By late afternoon, the UV index descends to 5 at 3:00 PM, before further decreasing to 3 at 4:00 PM and finally tapering off to 0 by 7:00 PM. This highlights the importance of sun protection during peak hours, particularly between 11:00 AM and 1:00 PM.
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 3 | moderate | 30 min |
| 08:00 | 5 | moderate | 30 min |
| 09:00 | 7 | high | 25 min |
| 10:00 | 10 | very high | 15 min |
| 11:00 | 12 | extreme | 10 min |
| 12:00 | 12 | extreme | 10 min |
| 13:00 | 11 | extreme | 10 min |
| 14:00 | 8 | very high | 15 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 |
During the year, the UV Index shows significant seasonal changes, peaking in the summer months. January and December have moderate UV levels (Index 4), with a burn time of 30 minutes. As spring approaches, February sees a rise to high levels (Index 6) and continues to climb sharply through March (Index 9), reaching April and May at extreme levels (Index 11). The highest UV readings occur in June and July (Index 12), accompanied by a burn time of just 10 minutes. As summer transitions to fall, the UV Index gradually decreases, with August still at extreme levels, followed by a slight drop in September (Index 10) and October and November returning to high levels (Index 6). It is crucial for residents and visitors to be particularly cautious during the high-risk months of April to August, taking protective measures such as wearing sunscreen, protective clothing, and seeking shade to minimize 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 |
| Hachijo | 4 | 6 | 9 | 11 | 11 | 12 | 12 | 11 | 10 | 7 | 6 | 4 |