Classification of New Zealand Synoptic Weather Types and Relation to the Southern Oscillation Index

Obliquely rotated T-mode principal component analysis has been applied to the NCEP/NCAR geopotential height reanalysis data for winter months from 1958 to 1996 over the New Zealand region. A new set of ten representative weather types were identified, with two being the most dominant. The temporal characteristics of the ten synoptic weather types were anlayzed in relation to different phases of the Southern Oscillation Index (SOI). While weather type-local meteorology relationships were consistent over time, the frequency of some weather types changed significantly with the SOI phases. In general, and relative to “normal” conditions, the frequency changes in El Niño years tended to be more significant than in La Niña episodes.