What is westeries ?

On the polar sides of the oceanic anticyclones lie zones where the wind direction becomes predominantly W’ly.  Unlike the Trades, these winds known as The Westerlies are far from permanent. 

The continual passage of depressions from W to E across these zones causes the wind to vary greatly in both direction and strength.  Gales are frequent, especially in w inter.  The weather changes rapidly and fine weather is seldom prolonged.  Gales are so frequent in the S hemisphere that the zone, S of 40°S, has been named the Roaring Forties.

In the N hemisphere fog is common in the W parts of the oceans in this zone in summer.