Last updated: August 1, 2025
Understanding the UV Index in Hachijo, Japan is critical for safeguarding your skin health in this picturesque island climate. With peak UV levels reaching as high as 12 around midday, awareness of UV exposure is essential to prevent sunburn and long-term skin damage. Hachijo experiences a temperate Cfa climate, which means sunny days can lead to elevated UV risks, especially during the summer months. Knowing the UV Index helps residents and visitors make informed decisions about sun protection, ensuring a safe and enjoyable experience under the sun.
The UV Index paints a vivid picture of the sun's intensity throughout the day, peaking at 12 between 11:00 AM and 12:00 PM, indicating a high risk of harm from unprotected sun exposure. As the morning progresses, the index rises from a manageable 2 at 7:00 AM to a significant 10 by 10:00 AM, urging early risers to apply sunscreen. The intensity begins to wane after 1:00 PM, where it drops to 8 at 2:00 PM, then further descends to 5 by 3:00 PM. By the evening, the UV threat decreases dramatically, settling at 1 by 5:00 PM and finally reaching 0 after 6:00 PM, signaling a safe window for outdoor activities. Staying informed about these hourly fluctuations can help ensure sun safety throughout the day.
| 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 | 11 | extreme | 10 min |
| 12:00 | 11 | extreme | 10 min |
| 13:00 | 10 | very high | 15 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 |