Last updated: August 1, 2025
In Koshigaya, Japan, being aware of the UV Index is crucial for safeguarding your skin health and preventing sunburn. Understanding the levels of ultraviolet radiation can empower residents and visitors alike to make informed decisions about sun exposure, especially during the peak hours of 10 AM to 2 PM, when the UV Index soars to a high of 11. With Koshigaya’s Cfa climate, characterized by warm summers and moderate UV exposure, it’s essential to stay vigilant. Whether you’re enjoying outdoor activities or simply running errands, knowing the UV Index helps you take the right precautions to protect your skin from harmful effects.
As the day unfolds, the UV Index reaches its peak during midday, providing an insightful glimpse into the sun's intensity. Starting from a modest 2 at 7:00 AM, the index climbs steadily, hitting 4 by 8:00 AM. By 9:00 AM, it escalates dramatically to 7, before soaring to its maximum of 11 at both 11:00 AM and 12:00 PM. As the afternoon progresses, the UV levels begin to ease, decreasing to 10 at 1:00 PM, then drifting down to 7 by 2:00 PM, and further to 5 at 3:00 PM. The descent continues into the evening, with the index dropping to 3 at 4:00 PM and tapering off to 1 by 5:00 PM, before settling at 0 by 7:00 PM. This data serves as a reminder to stay sun-safe, particularly during those peak hours!
| Time | UVI | Category | Time to Burn |
|---|---|---|---|
| 07:00 | 2 | low | 45 min |
| 08:00 | 4 | moderate | 30 min |
| 09:00 | 6 | high | 25 min |
| 10:00 | 9 | very high | 15 min |
| 11:00 | 10 | very high | 15 min |
| 12:00 | 10 | very high | 15 min |
| 13:00 | 9 | very high | 15 min |
| 14:00 | 7 | high | 25 min |
| 15:00 | 4 | moderate | 30 min |
| 16:00 | 2 | low | 45 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 shows significant seasonal variations, indicating changes in the potential for skin damage. From January to February, the UV Index is moderate (3-5) with a burn time of 30 minutes. As March approaches, the UV Index rises sharply to 8, marking the beginning of high-risk months, which continue through July when it peaks at 11 (extreme exposure). The highest risk persists until August with UV levels remaining very high. From September to October, the index gradually declines to 7 and 5, transitioning back to moderate levels by November and December. Visitors and residents should exercise caution during high-risk months (March to August), limiting sun exposure, and using protective measures like sunscreen and clothing to prevent skin damage. Regular monitoring of UV levels is advisable, especially in the peak summer months when the risks are greatest.
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 |
| Koshigaya | 3 | 5 | 8 | 9 | 10 | 10 | 11 | 10 | 9 | 7 | 5 | 3 |
| 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 |