An area of low pressure is travelling from the southwest and moving up the country, which brings with it wet weather.
A heavy rain warning was in place for Fiordland from 1pm today until 1pm tomorrow and areas including Dunedin, Nelson and the Kapiti Coast could expect showers.
Wellington City might scrape by without rain, Adams said.
"On the whole, the rest of the country will be dry. There's just the odd chance of the shower through the central plateau."
Maximum temperatures on Sunday and Monday
Gisborne: Sunny; 24 and 25 degrees on Sunday and Monday
Whangarei: Fine with rain; 26
Wellington: Cloud, rain, and sun; 20 and 22
Hamilton: Sun and rain; 25
Tauranga: Mostly sunny, with cloud; 26 and 24
Auckland: Sun, rain; 24 and 25