“Howl, O gate! Cry out, O city!” The word “howl” could also be translated as “wail.” This is the figure of speech personification. [For more on personification, see commentary on Prov. 1:20].
“for smoke comes out of the north.” It has been suggested that this might be the dust kicked up by the approaching army, but the use of “smoke” makes it much more likely that as the Assyrian army approached from the north they were burning the cities they conquered.
“and there is no straggler in its ranks.” The meaning of this phrase likely refers to the fact that the Assyrian army was confident and well-disciplined. There were no stragglers and no deserters.