The UV index can be strong through cloud even when the sun isn't directly shining.

即使没有阳光直射， 穿过云层的紫外线指数也会很强。

The UV index (the strength of the sun) can be high at many times of the year - it doesn't have to be hot.

一年中的很多时候紫外线指数（太阳的强度）可能很高 - 不一定很热。