Last updated: June 2, 2025
Understanding the UV Index is essential for residents and visitors in Hakone, Japan, where the stunning natural landscapes can lure you outdoors but also expose you to harmful ultraviolet rays. Monitoring UV levels is crucial for preventing sunburn and maintaining skin health, especially during peak sunlight hours. With Hakone's Cfa climate, typical UV exposure can range dramatically throughout the day, climbing to a severe 11 between 11:00 AM and 12:00 PM. Being informed about the UV Index allows you to take protective measures, ensuring you can enjoy Hakone’s beauty while safeguarding your well-being under the sun.
The UV Index experiences a dramatic rise as the day unfolds, peaking in the late morning to early afternoon. Starting at a low 2 by 7:00 AM, it escalates to a moderate 5 by 8:00 AM, before soaring to a striking 10 at 10:00 AM. By 11:00 AM and 12:00 PM, the UV Index reaches its zenith at 11, indicating a very high level of UV radiation that calls for protective measures. As the afternoon progresses, the index begins to decline, falling to 8 by 2:00 PM and gradually dropping to 5 at 3:00 PM. By 4:00 PM, it slips further to 3 and dwindles to 1 by 5:00 PM, finally settling at 0 after 6:00 PM. This pattern highlights the crucial hours for sun safety, especially between 11:00 AM and 12:00 PM, when UV exposure is at its highest.
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 2 | low | 45 min |
| 08:00 | 5 | moderate | 30 min |
| 09:00 | 8 | very high | 15 min |
| 10:00 | 10 | 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 |
Throughout the year, the UV Index demonstrates notable seasonal changes, with the most intense exposure occurring from April to August. During these months, the UV Index reaches extreme levels (10-12), significantly reducing the burn time to just 10 minutes. March and September also pose risks with very high levels (8-10), allowing for a burn time of only 15 minutes. Consequently, February and October present high levels (6-7), where protective measures are still advised with adjusted burn times of 25 minutes. Residents and visitors should exercise caution and protect their skin, especially during the high-risk months of April through August, by using sunscreen, wearing protective clothing, and limiting sun exposure during peak hours.
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 |
| Hakone | 4 | 6 | 8 | 10 | 11 | 11 | 12 | 11 | 10 | 7 | 5 | 4 |
| Osaka UVI | 4 | 6 | 8 | 11 | 11 | 11 | 12 | 11 | 10 | 7 | 5 | 3 |