It's a hard rain's a-gonna fall.

那瓢泼的暴雨就要落下。

The hard rain lasted roughly half an hour without break.

那场暴雨持续约半小时而未有间歇.

The rain decreased to hard rain that soaked seeds waiting for moisture in the desert soil.

暴雨逐渐下降为大雨，浸泡着在沙漠土壤里急需水分的种子。