It's only seven days and counting to the official start of spring.

The official meteorological start to spring is next Tuesday, September 1, and on that date reliable long range data is showing the chance of a small but sub-tropical low dropping down over northern New Zealand.

Flowers have already started to bloom ahead of the official start of spring next week. Photo: File.

The WeatherWatch website says sub-tropical lows don't automatically create severe weather, but they can rapidly deepen and bring areas of very heavy rain and localised gusts.

'With the low expected to deepen as it crosses over New Zealand on Tuesday and Wednesday next week, it's one to watch,” says a statement from the weather organisation, 'but it remains at the lower end of the risk scale.

'While borderline, if the low drops far enough south and deepens east of Hawkes Bay next Wednesday it may also bring in some rain to dry parts of North Canterbury, perhaps on Thursday.

'Although south of Christchurch may not receive a drop from this low, which indicates how borderline it is there.”

This sub-tropical low will be followed by a Tasman Sea low just a few days later next weekend.

'Neither lows look too serious,” they add, 'but the sub-tropical elements means those with concerns should be up-to-date with the latest long range maps to track where any intense pockets of weather might be.”

The two lows means spring will kick-off with mild temperatures for many areas, although by next weekend the Tasman Sea low may bring in a brief cool southerly for the South Island.