A cold southwesterly airflow that is spreading northwards over New Zealand today will lead to colder than average tempeartures overnight. A few coastal spots may be near normal. Overnight lows in the map below are represented by numerical figures for a few various centres around New Zealand. The colour shaded areas are the departure from normal figures.
This second map here below shows Saturday’s highs and departure from normal figures. So for example the inner South Island is going to be in the region of 4 to 8 degrees above normal for the time of year tomorrow while eastern coastal areas Canterbury northwards are going to be 4 to 8 degrees below normal in spots. More then likely the actual departure from normal figures will be at the lesser end of those ranges, so 4 to 5 degrees above normal and 4 to 5 degrees below normal.
This warming in the inner South Island is due to a hint of northwest airflow starting to make it’s presense felt while the cool eastern temperatures are due to today’s cold southwest airflow still clinging on but it will slowly depart making for a warmer Sunday.