I did a "round the horn" cruise 2 years ago and we hit REALLY rough seas one night just outside of Buenos Aires (furniture sliding across the room, gift shop/liquor store destroyed, tables overturned, passengers injured, etc). But only bad for a few hours.
Also too rough to disembark by tender at Puerto Madryn so we skipped that port of call. Rest of trip was smooth.
Also ... pack clothes that you can layer. No real need for extra heavy jackets, but I recommend that you bring thermal underware to go under your lighter weight clothing and a good wind breaker.