Thunderstorms could be bring hail to southern parts of the country, while there is a risk they could also hit parts of the North Island, including the Bay of Plenty.
Any thunderstorms are expected to produce localised heavy rain of 10 to 20 millimetres per hour and hail of 10 to 20mm diameter, MetService says, warning people to keep an eye on rivers and streams in affected areas.
Meanwhile a ridge of high pressure is forecast over much of the country during the next few days, and that will bring largely settled weather for most.
"However, there will be showers building over inland areas as the heat of the sun drives convection in the afternoon and evenings,” says the MetService.
“While the surface pressure charts for midnight tonight and midnight Monday look very similar, upper atmosphere conditions tomorrow will be significantly more favourable for any showers to build into potential thunderstorms.”
Looking ahead to the rest of the week, MetService said settled conditions are expected over much of the country during Tuesday and Wednesday, although a few areas may see a shower or two.
A broad ridge of high pressure follows a front over the South Island later in the week. The front is expected to reach the lower South Island late on Thursday, which moves slowly northeast on Friday. It's expected to bring a period of rain to much of the South Island, with heavier falls expected about Fiordland and southern Westland. There is a low risk that will reach warning amounts about Fiordland and southern Westland from late Thursday to Friday.
In Auckland, morning drizzle is forecast to turn into showers during the day. MetService forecast a high of 21 degrees Celsius.
It's mostly cloudy in Hamilton with the possibility of a shower; a high of 20C is expected.
A mostly cloudy day in Tauranga and the chance of an afternoon or evening shower, with a high of 19C.
It should remain fine and sunny all day in Wellington with light winds, and a high of 18C.
In Christchurch, low cloud or morning fog is expected to lift revealing a fine day and a high of 21C.
A few showers develop over Dunedin in the morning which could turn heavy and bring thunder and hail by the afternoon, but conditions are expected to clear by the evening. A high of 17C.