The Collaborative International Dictionary of English v.0.48:

Northwesterly \North`west"er*ly\, a.
   Toward the northwest, or from the northwest.
   [1913 Webster]

WordNet (r) 3.0 (2006):

northwesterly
    adj 1: coming from the northwest; "northwesterly winds" [syn:
           northwesterly, northwest]
    2: situated in or oriented toward the northwest [syn:
       northwestern, northwesterly, northwest]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "northwesterly":
   NNW, NW, NW by N, NW by W, antarctic, arctic, austral, boreal,
   east, eastbound, easterly, eastermost, eastern, easternmost,
   hyperborean, meridional, north, north-northwest, northbound,
   northeast, northeasterly, northeastern, northerly, northern,
   northernmost, northwest, northwest by north, northwest by west,
   northwestern, northwestward, northwestwardly, northwestwards,
   occidental, oriental, south, southbound, southeast, southeasterly,
   southeastern, southerly, southern, southernmost, southwest,
   southwesterly, southwestern, west, westbound, westerly, western,
   westernmost