relent

今度はCNNの記事からです。暑さは週末も和らがないようです。

Heat won't relent in scorched Southwest

(CNN) -- If you think a place called Furnace Creek would be hot in the summer, you're right. The town in California's Death Valley is expected to hit 128 degrees Saturday.

And the heat will stay on full blast through Tuesday, at least. At night, the mercury will drop to a refreshingly cool 96 degrees.

Fun aside, the heat wave scorching the Southwest is dangerous, as 170 concert goers found out Friday evening in Las Vegas, according to the fire department.

http://edition.cnn.com/2013/06/29/us/southwest-heat/index.html?hpt=us_c2

relentは「＜人が＞優しくなる、同情的になる、（厳しい決定を下した後で）態度を軟化する」という意味の他に、「＜厳しい天気などが＞和らぐ、弱まる」という意味もあります。（『ジーニアス英和辞典　第４版』大修館）
Macmillan Dictionaryに"if rain or snow relents, it stops being so severe"とありました。(Hatahata)