Relationships between New Zealand rainfall and south-west Pacific pressure patterns

The relationships between New Zealand regional rainfall and south-west Pacific pressure patterns are investigated. Principal components of monthly sea-level pressure are computed from 14 Australasian climate stations and interpreted as physical features of the circulation near New Zealand. Monthly rainfall data at eight New Zealand locations are regressed against these components revealing significant relationships, although the percentage of explanation seldom exceeds 50%. At almost all New Zealand locations the dominant pressure-rainfall relationship is that with the first principal component. The physical interpretation of this component varies slightly from month to month, however, in general it represents the strength of prevailing westerlies or south-westerlies over New Zealand, as described by the location and intensity of regions of high pressure. Other principal components relate to the direction of airflow over New Zealand, to which rainfall at some stations is very sensitive. The relationships described in this paper further advance the understanding of the large-scale processes that contribute to the weather and climate of New Zealand. (C) 1998 Royal Meteorological Society.