The Collaborative International Dictionary of English v.0.48:
Southwestward \South`west"ward\, Southwestwardly \South`west"ward*ly\, adv. Toward the southwest. [1913 Webster] SouvenanceWordNet (r) 3.0 (2006):
southwestwardly adv 1: in a southwestward direction [syn: southwestward, southwestwardly]