Beware of extreme ultraviolet rays today and stay out of the sun between 10 a.m. and 4 p.m. to protect your skin, the National Weather Service advises.

The UV index for Honolulu about noon today is 12, which falls in the “extreme” exposure category, the highest of five in the index. The extreme category begins at 11.

A higher UV index means there is more skin-damaging UV radiation present and skin damage occurs more quickly, the weather service said.

A severe sunburn can result from overexposure, and skin cancer can develop from frequent burns or long-term exposure.

UV exposure levels are typically higher in Honolulu because the arc of the sun is higher over the islands. For Honolulu, UV levels typically begin entering the extreme category in April and peak in the summer, according to historical data on the National Weather Service’s website. Last year, UV levels stayed within the extreme category throughout the summer and fell to a lower category in September.

Honolulu today has the second-highest UV index — behind only San Juan, Puerto Rico, which has a UV index of 14 — of about 60 cities listed in the National Weather Service’s UV index forecast. The level for Saturday was 8.

To protect your skin during extreme exposure levels, the weather service recommends wearing protective clothing, sunglasses and sunscreen.