The major influences on the climate of the West Coast.
The West Coast has a noticeably milder climate than the east coast regions, with fewer extremes of climate. Greymouth's sunshine hours of 1980, and Hokitika's of 1964 are ahead of Auckland's 1825.
By national and international standards the region receives a generous and reliable rainfall. Near the Main Divide this exceeds 8000 mm annually - declining to a more manageable 2000 mm at the coast. At high altitudes there are snowfalls all year round. In the region’s southern parts this contributes to glaciers that reach to within a few hundred metres above sea level.
However, away from these areas, the climate is generally mild and near the coast sunshine hours are similar to those experienced on the east coast.
Surface winds do not reflect the prevailing westerly flow at higher altitudes. More sheltered locations provide a variety of different microclimates, with warm moist north-westerlies common.
Weather systems crossing the region produce marked changes in wind direction and air mass characteristics. The approach of fronts produces a warm moist airflow of tropical origin. The passage of a front is usually followed by a cold dry airflow of polar origin. In both cases the air travels considerable distances over the open sea, the nearest land mass being over 1600 km distant. As a consequence, the air quality is generally high.
A low pressure area to the east of the South Island may promote an easterly airflow over the region. On these occasions, particularly in winter, strong easterly winds may descend down major river valleys. In more sheltered inland locations, cold air may be trapped in valleys forming temperature inversions.
Winters are often sun-filled, with few frosty mornings, even in south-westland, while springtime is traditionally wetter. Northern areas such as Karamea border on sub-tropical.