You could say, " It's pissing down today."

“今天下大雨”。

My favourite one: " it's pissing it down outside! "

上天在撒尿。

It's dark and pissing down rain when they land in London around nine in the evening, and he and Cash are both soaked the second they climb out of the car inside the back gates of Kensington.

当他们晚上九点左右抵达伦敦时， 天色漆黑，还下着倾盆大雨，他和卡什在肯辛顿后门下车时就浑身湿透了。