According to Wikipedia,
...during a global dust storm the diurnal temperature range narrowed sharply, from fifty degrees to only about ten degrees, and the wind speeds picked up considerably—indeed, within only an hour of the storm's arrival they had increased to 17 m/s (61 km/h), with gusts up to 26 m/s (94 km/h).
Another source claims that,
Typical wind speeds in the Martian atmosphere exceed 200 km/hr (or 125 miles/hr). Gusts can often reach 500 to 600 km/hr (or 300-375 miles/hr).
However, (again from Wikipedia)...
The low density of the Martian atmosphere means that winds of 18 to 22 m/s (65 to 79 km/h) are needed to lift dust from the surface.
I haven't done the math, but I doubt that 500 km/h could toss a person around, if 65 km/h can barely toss dust around. So basically, it seems like this is a narrative device, just like the Earth-normal gravity they seem to be portraying, when Mars barely has 1/3 of Earth's gravity.
That being said, it does appear to be an unusually intense storm, in-universe. Even if storms of that power aren't normal in the real world, I doubt they're impossible. This book/movie simply features one of those rare occurrences.