ある暖かくて湿気の多い日に太陽の沈むのを見れば、湿気のために太陽の形が変わって見える。

English Translation

If you watch the sun setting on a warm, damp day, you can see the moisture changing the shape of the sun.

Unnatural word-for-word translation… My alternative translation is:

暖かく湿気の多い日には、湿気の影響で太陽が歪んで見える。(あたたかくしっけのおおいひには、しっけのえいきょうでたいようがゆがんでみえる)

Here are problems in the original translations:

  • ある is super redundant. This is about the science. Every time the weather is warm and damp, the same phenomenon always happens. Inserting ある in this context, there was only one day that the phenomenon happened.

  • Repeating the verb 見る twice is redundant.

  • 湿気の「ために」is understandable but awkward.

  • 太陽の形が変わって is unnatural. 歪む means “to get distorted”.