Radak: It is when the enemy will come.

Rashi: It is the Am after they will all be exiled.

Rashi #1: The wind sweeps even fields [irrigated via] streams, and makes them Midbar (desolate).

Rashi #2: A dry wind on mountains in the Midbar. Radak - this is like "v'Hisbi'a b'Tzachtzachos Nafshecha (Yeshayah 58:11). It will dry the land and make it desolate.

Radak: It is a clear ¹ wind that goes unobstructed on mountains or in a wilderness. If a wind goes amidst settled areas, then houses, walls and fences block it. So the enemy will not be impeded. It will come just like it wants - with great masses, horses, cavalry, and splendorous dress.

Malbim: Wind can help (a) to clear clouds from the sky, and enable clear light [from the sun]; (b) to winnow. A dry wind (when there are no clouds) does not do the former, and winnowing is not done in the mountains. Such a Ru'ach has no benefit. Also the Ru'ach of the false Nevi'im has no benefit! Nevu'ah of rebuke helps in the city, when people hear it. It separates the chaff from the grain (Resha'im from Tzadikim). And even when it is not heard, in the Midbar, it can clear the sky. People see what decree Hashem wrote about them above. The Ru'ach of the false Nevi'im does neither - it does not make people repent, nor does it tell the future.

Rashi: This wind will not be helpful to winnow (remove chaff from grain), nor to clean grain. It is only harmful, to exile men, children and animals. Radak - when a wind is not too strong, even though it harms some matters, there is benefit from it. No good will come from this wind.

Malbim: Refer to 4:11:3:4.