A feed of sub-tropical air is bringing rain and warmer temperatures to New Zealand for the first working week of spring, a distinctly different feel to the cold southwesterlies which dominated the last month of winter.

"A slow-moving front is bringing periods of heavy rain to Auckland and the Coromandel Peninsula," says MetService Meteorologist Jessie Owen.

"Due to the slow nature of this weather feature there is a risk it could become stationary over a particular area for some time leading to higher rainfall accumulations for localised areas. Heavy Rain Watches have been issued for these regions and people are advised to keep up to date at www.metservice.com."

On Tuesday afternoon and evening there is a risk of thunderstorms developing about western parts of Auckland and Northland.

If these thunderstorms arise they are likely to bring impactful downpours to these areas.

It is important for people to check back in with the severe weather warnings at http://bit.ly/AllWarnings as further Heavy Rain Watches may be issued to cover this period, says Jessie.

The sub-tropical air is also having an effect on temperatures this week.

Many places in the North Island as well as eastern parts of the South Island are forecast to crack 20°C, with the warmest day of the week looking to be Wednesday.

Overnight lows are also expected to be significantly warmer, with no sign of the frosts from last week.

The next weather system to affect the country is a trough from the Tasman Sea.

This will bring a period of rain to western parts of both islands on Tuesday and Wednesday, and Heavy Rain Watches have been issued for Mt Taranaki, western Tasman, and the West Coast Region.

Eastern areas will be spared from much of this rain and can expect fine and warm weather for most of the week.

Finally, to round out the week another high pressure system is forecast to bring settled weather to the country by Friday.

For a sneak peak at what else is expected this September check out the latest MetService long-range forecast at http://bit.ly/MonthlyOutlook to see when southwesterlies are expected to return this month.