The same weather system which brought flooding to parts of southeast Australia last week is drifting towards New Zealand.
The system will bring with it heat and humidity, which could trigger thunderstorms and torrential downpours across northern and western regions of the North Island later today, WeatherWatch said.
The downpourscould be heavy enough to cause localised surface flooding.
But while some communities could be hit by rainfall heavy enough to flood, a kilometre away it might only be drizzling, and another kilometre away it might be sunny.
"This is the nature of this fairly weak low that is moving in - the cloud mass surrounding it is very much alive, shrinking and growing all the time - and it's this constant change that makes it tricky to time things and to be more specific," WeatherWatch said.
On Tuesday and Wednesday there could still be heavy downpours for some areas - particularly inland - and the North Island would receive the bulk of the rain, while southern and eastern areas of the country should be the driest.
But despite the rain it would feel hotter than it was, WeatherWatch said.
Highs would be in the low to mid 20s this week, but it would feel like in the late 20s and low 30s at times.
"So far this summer we've had some very humid days, but without the heat many people haven't really been aware of it."
