The Collaborative International Dictionary of English v.0.48:

Southwester \South`west"er\ (?; colloq. ?), n.
   1. A storm, gale, or strong wind from the southwest.
      [1913 Webster]

   2. A hat made of painted canvas, oiled cloth, or the like,
      with a flap at the back, -- worn in stormy weather.
      [1913 Webster]

WordNet (r) 3.0 (2006):

southwester
    n 1: a strong wind from the southwest [syn: southwester,
         sou'wester]