Here’s what is making the weather headlines this weekend.

INSTABILITY BEGINS

Today holds the potential for downpours and thunderstorms in both Islands, but storms in the North and South Islands occur for different reasons.

Any thunderstorms that occur for the North Island are the result of converging winds at the surface (pre frontal trough) and high surface moisture + heat, this overcomes any warm upper air and makes the atmosphere unstable. Upper level wind shear also helps much like wind going across the top of a chimney creates a good draw on a fireplace.

Storms for the South Island especially about Southland and Otago this afternoon occur due to converging winds at the surface but also a main factor will be cold upper air moving over. Around 5000m up in the atmosphere the temperature will be -22 degrees versus the storms for the North Island where at the same level it will only be about -14 degrees. There is a chance thunderstorms may sneak up into South Canterbury also.

Another round of thunderstorms will occur on Sunday.

Information on storms today and tomorrow can be found from Metservice here.

PLEASANT FOR CANTERBURY

Canterbury would seem to have the best weather around the country today if light winds, warm temperatures and some sun are in mind. Temperatures in the low to mid twenties are likely. The only hiccup could be a few showers moving into South Canterbury later this afternoon or evening.

While other regions around the country get warm temperatures also they may not be as dry all day long or see as much sun. Still, good weather can be had at various times for different places, Southland and Otago may be off to a cracker start but then heavy showers develop this afternoon for example.

WEATHER ON SUNDAY

A front lies over the North Island meanwhile the South Island has low pressure and a series of troughs.

North Island

Showers, becoming heavy in the afternoon with thunderstorms possible then easing in the evening. The east coast is a bit cloudy with showers or some rain developing in the afternoon spreading from the west, clearing at night. Taranaki, Wellington and Wairarapa stay dry for much of the day though with morning cloud breaking to some sun. Winds are mostly light coming in from the northwest, southwesterlies for western Waikato up through to western Northland.

South Island

Showers for the West Coast, an isolated heavy fall or two is possible, Fiordland and perhaps South Westland brighten up in the afternoon. A mix of sun and cloud elsewhere, isolated showers develop in the afternoon for most other regions with a chance one or two may become heavy with thunderstorms, the greater risk for any storms is about inland hills and ranges of the lower South Island with a lesser risk elsewhere. Nelson and more so Marlborough may stay dry all day long. Winds coming in from the north or northeast, perhaps a little more east to southeast for Southland and Otago.

• 

•