Why does it say "Chazak v'Amitz"?
Malbim: Chazak refers to a hailstorm; Amitz - persistence of strength without wearying - refers to a flood [that breaks cedars].
What is strong like a hailstorm?
Rashi: A wind.
Radak: It is a strong day on which Hashem will come against them like a hailstorm that fells trees and breaks them. Malbim - it breaks, but it does not flood (carry away) things from their place. If it joins with "Sa'ar Ketev" (great wind), it will uproot everything; a flood will carry everything far away. The hail is a metaphor for the killing and destruction that Ashur did in their land; the flood is exiling the remnant to Nehar Gozen and the cities of Madai.
What is "Sa'ar Ketev"?
Rashi: It is the storm of Ketev Merari (a demon - Pesachim 111b).
Radak, Malbim: It is as if it says k'Sa'ar; the prefix Kaf in "k'Zerem" applies also to this. Sa'ar is a storm wind that destroys and cuts down everything. [The day] is compared also to an awesome flow of water, which floods everything that it passes over. It fells tall trees.
What is the meaning of "Hini'ach la'Aretz b'Yad"?
Rashi: [The wind] will uproot the figs from the tree and cast them on the ground, forcefully.
Radak: This is like Yani'ach; past tense is used in place of future; this is common [in Nevu'ah]. This strong day will place the crown of their pride on the ground "b'Yad", i.e. by force.
Malbim: The flow of hail and great water, first it placed the crown of pride on the land, in its hand
