Force in terrible tornado back and forth (2-3-3)
I believe the answer is:
to-and-fro
'back and forth' is the definition.
(I know that back and forth can be written as to and fro)
'force in terrible tornado' is the wordplay.
'force' becomes 'F' (symbol used in Physics e.g. f=ma).
'in' indicates putting letters inside.
'terrible' is an anagram indicator.
'tornado' with letters rearranged gives 'toandro'.
'f' inserted within 'toandro' is 'TO-AND-FRO'.
(Other definitions for to-and-fro that I've seen before include "Hither and thither" , "Back and forth" .)