Storm encountered on way up — a pain (7)
I believe the answer is:
tempest
'storm' is the definition.
(tempest is a kind of storm)
'encountered on way up a pain' is the wordplay.
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'on way up' says the letters should be written in reverse.
'a pain' becomes 'pest'.
'met' backwards is 'tem'.
'tem'+'pest'='TEMPEST'
(Other definitions for tempest that I've seen before include "Violent windy storm" , "A great storm of wind and rain" , "Wild storm" , "Violent Shakespearian storm" , "Bad weather" .)