What is the meaning of "Niteches"?
Rashi: It descends and touches, like "u'Matar Lo Nitach Artzah" (Shemos 9:
Radak: This shows how quickly it will come on them, like something that is poured.
Malbim: The anger is poured on those who anger Me; via this, the place will be destroyed with everything in it - people, animals, vegetation - fruits of the tree and of the ground.
Why does it say "Niteches" (feminine singular)? It discusses also Af, which is masculine!
Radak: When the subject is something masculine and something feminine, the conjugation is like the one next to the verb, whether it is first or last, e.g. "va'Tdaber Miryam v'Aharon b'Moshe" (Bamidbar 12:1), "va'Tichtov Esther? u'Mordechai" (Esther 9:29), "va'Tochal Hi va'Hu" (Melachim I, 17:15), "Garei Veisi v'Amhosai l'Zar Tachshevuni" (Iyov 19:15).
Why does it mention burning, but not the fire?
Radak: Anger is heat; the nature of fire in man produces anger (so it is as if it was mentioned).
Why does it say "v'Lo Sichveh"?
Malbim: One who is ill has a remedy via foods and herbs - but when there is Chemah (burning anger) also on vegetation, and it rots, animals and people get ill without remedy.