Northernly, southernly, westernly, and easternly are unnecessary words. The standard adjectives/adverbs are northerly, southerly, westerly, and easterly—without the n. Similar words that combine directions—for example, northeasterly, southwesterly—also go without the n.
These writers use these directional words well:
Biting easterly winds, forcing temperatures down well below the January average, are expected to continue for the next few days. [Bournemouth Echo]
Conditions are expected to be ideal for bushfires with temperatures reaching 35 degrees and above with dry northerly winds. [Cooma Monaro Express]
Before that happens, a brisk southwesterly wind will aid in enough warming to get the area near freezing today. [Rockford Register Star]
For more on the usage of these words, see our entry on directional words.
