J'aurai sûrement un quart d'heure de retard
I will probably be fifteen minutes late
Je serai sûrement en retard d'un quart d'heure.
I will probably be fifteen minutes late.
Checking online at Larousse etc., I don't see that "sûrement" means "probably". "Probably" introduces doubt. Why not use "surely" or "certainly"?
Or for the French, "probablement"? Which does seem to mean "probably".