Weather Brief 17 July: Spring-Like Temperatures and Settled Weather for the Rest of the Work Week

With an area of high pressure north of Aotearoa we are in for a few days of mostly settled and dry weather. Thanks to westerlies and northwesterlies, some spring-like temperatures are also on its way to big parts of the country.

Wednesday: Westerlies will bring pockets of scattered showers to the upper North Island throughout the day. Drier conditions for the lower North Island, but a few afternoon showers can’t be ruled out for the Wellington region.

Canterbury is the place to be on Wednesday with wall-to-wall sunshine expected! More clouds and showers along the lower west coast, while the upper South Island should stay mostly dry.

Temperatures across the country:

Auckland L:8°C, H:15°C

Wellington L:8°C, H:12°C

Christchurch L:3°C, H:12°C

Hamilton L:6°C, H:13°C

Tauranga L:8°C, H:15°C

Dunedin L:9°C, H:14°C

Wednesday Outlook


Westerlies will continue to bring showers along the west coast of the South Island, while the east coast should stay dry. The lower North Island is in for a dry day as well, while the north will be dealing with some showers. Winds should stay relatively light across the country and temperatures will warm to above average for this time of year.

Thursday Outlook


Another day of mostly dry conditions in the east, but a moist onshore flow can bring showers to the west coast of both island. Temperatures will continue to stay well above average, especially along the east coast of the South Island where it will feel more like spring than winter! An area of low pressure will track towards the west coast of the South Island and can bring some heavy rain with it just in time for the weekend.

Two Day Rainfall Map

This map shows the extent and intensity of rain that’s expected to affect New Zealand during the next two days.

Click the map to view the animated forecast.


NIWAWeather keys

The colour gradient you see behind your town or city forecast depicts the amount of cloud cover expected during daylight hours - ranging from clear blue to dark grey (overcast). If rain or snow is expected, raindrop or snowflake symbols will also appear in the background. The further down the screen the symbols appear, the heavier we expect the rain or snow to be. Read more...

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NIWA is the National Institute of Water and Atmospheric Research. We’re New Zealand’s leading supplier of atmospheric, freshwater, environmental and marine science services.

We collect, store and manage data on New Zealand’s weather, climate, marine and freshwater resources and other important environmental parameters. We deliver that data via a range of tools and services that help Kiwis manage their interactions with the environment and its resources more productively and sustainably.


Meet FitzRoy

He’s the 18-tonne brain behind NIWAWeather’s forecasts. His real name is IBM p575 POWER6, but he prefers FitzRoy – or just ‘supercomputer’ if he’s in one of his moods.

He’s a fussy individual. He occupies a specially constructed, climate-controlled (appropriately!) room at NIWA’s site in Wellington. But we don’t mind, because he works tirelessly, 24/7, with the computational effort of about 7000 laptops. And his outputs are vitally important to all New Zealanders.


Weather Q&A

What causes heavy rain, versus light rain?

The amount of water vapour present in a cloud, and the strength of the rising air ('updraft') in that cloud, determines the intensity of rain it can produce. The depth, or thickness, of cloud determines how much water is available.

The heaviest rain is usually associated with very deep clouds such as thunderstorm cells, which may extend from about one kilometre above the Earth’s surface to over 10 kilometres high. These clouds also contain very strong updrafts, which means large drops of rain can be held up in the cloud until they grow so big that the rising air can no longer support them.

Prolonged heavy rain can also fall from very thick, slow-moving stratiform clouds known as nimbostratus.

In New Zealand, the heaviest rain usually falls on the western side of the mountain ranges, where moisture-laden winds are forced upwards by the mountains, creating very deep clouds.

How does rain come out of clouds?

For rain to fall, the water vapour that makes up clouds needs to combine and grow into droplets heavy enough to counteract rising air (‘updrafts’) in the cloud. But the process relies on more than water alone. Tiny specks of dust and other microscopic substances, known as ‘condensation nuclei’ are required. Condensation nuclei are everywhere in the atmosphere. Water vapour wraps itself around them, which begins the process of raindrop growth. As the drop gets bigger, it collides with more and more droplets and growth accelerates until the drop is heavy enough to fall.

How is rain measured?

Forecasters use a plastic or metal open-topped cylinder called a rain gauge to capture rain. Rain gauges have standard dimensions so that measurements can be compared from place to place. The amount of rain collected is measured over a certain timeframe – usually hourly or accumulated over 24 hours. Measurements can be made manually or electronically. In New Zealand we measure rain in millimetres. Ten millimetres of rain in Wellington means that if all the rain that fell within the city was spread out over hard flat ground (so it couldn’t drain away), it would form a puddle 10 millimetres deep.

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