The plot below shows the forecast wave heights and directions for the next week.
The forecasts come from the NOAA global wave forecasting model Multi WaveWatch3 (MWW3) for a node at 173° E 43.5° S which is in Pegasus Bay,
21 km E of Waimairi Beach and 17.5 kn NE off the entrance to Lyttelton Harbour, as shown here.
Of particular interest are waves from the directions
between ENE and ESE (67.5 and 112.5°N)
because these waves generate IG waves at Sumner Head,
as presented here.