Radak: It is the rain that falls in Cheshvan. It is called Yoreh and Moreh. Yoreh is in Cheshvan and Malkosh is in Nisan (Ta'anis 5a). These are the two times that grain needs the rain. Usually, most of the rain falls in Cheshvan. Therefore it is called Yerach Bul; this is like Mabul. That rain is called Revivim; elsewhere it is called Yoreh.

Rashi: It is the latter rain that falls in Nisan on the sheaves and straw.

Radak: The verse teaches that rain was withheld due to your evil deeds, like the Torah says "v'Sartem va'Avadtem Elohim Acherim

Radak: You refused [to accept] the rebuke of the Nevi'im; you were not ashamed of them.