Auckland would see some showers today, particularly in the west, with rain developing tonight.
Tomorrow the front would bring showers from Northland to Taranaki, with better weather for Kapiti and Manawatu, Mr Law said.
WeatherWatch said a fairly dry morning in the North Island today would turn to rain or showers this afternoon in Taranaki and the lower North Island, with cloud thickening in northern and western areas.
A southerly change in Wellington would also bring cooler temperatures, dropping the high to just 12C on tomorrow.
Main centres Tuesday:
Auckland: Chance of a few showers, mostly in the west, cloudy afternoon, rain developing tonight. High 19C.
Wellington: Cloud increasing and spots of rain, southerly bringing more showers this evening. High 16C
Christchurch: Showers and rain, cloud thickening during the day, rain spreading north. High 13C.
Dunedin: Cloudy start, showers clearing, improving through the afternoon. High 12C.
Source: MetService