雨が土砂降りだ。

雨が土砂降りだ。

It's raining cats and dogs.

雨(あめ)が土砂降(どしゃぶ)りだ。

Ame ga doshaburi da.

雨 (あめ)

rain

が (が)

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

土砂降り (どしゃぶり)

downpour; pouring rain; cloudburst; pelting rain; heavy rain

だ (だ)

be; is; indicates past or completed action; indicates light imperative

Readings: ウ、あめ、あま-、 -さめ

Meaning: rain

Readings: ド、ト、つち

Meanings: soil, earth, ground, Turkey

Readings: サ、シャ、すな

Meaning: sand

Readings: コウ、ゴ、お.りる、お.ろす、ふ.る、ふ.り、くだ.る、くだ.す

Meanings: descend, precipitate, fall, surrender