Latest information on North Island thunderstorms 6 December 2012

Around midday on Thursday 6 December an active trough line passed slowly through Auckland. One of these thunderstorm cells contained a tornado which touched down near Hobsonville, tragically killing three people.

This blog post has been set up to keep you informed of the latest developments in this weather system as it travels south-east from Auckland.

Auckland radar image at 12.15pm 6 Dec 2012

Auckland radar image at 12.15pm 6 Dec 2012

Situation update as at 9.30am 7 December 2012

Further squally showers and one or two thunderstorms are expected in the West from Auckland to the Kapiti Coast today. We could see gusts to 110km/hr accompanying heavy showers. There is also a potential for small hail to 10-15mm. Showers clear overnight and the weather looks mostly dry for Auckland over the weekend.

Update as at 6.00pm 6 December 2012

Severe Thunderstorm Watches and Severe Thunderstorm Warnings have been lifted. This is the last blog update for today, but keep an eye out for tomorrow’s weather as there are still Severe Weather Warnings and Watches in place for heavy rain and gales in places. The Severe Thunderstorm Outlook is still in place here: http://metservice.com/national/warnings/severe-thunderstorm-outlook

Update as at 5.00pm 6 December 2012

A report of a tornado in Ngongotaha refers to part of the same system that struck Hobsonville earlier in the day, and has been the subject of Severe Thunderstorm Warnings. This cell is now moving over Mahia and out to sea.

Update as at 4.30pm 6 December 2012

The last active thunderstorm is moving in towards Lake Waikaremoana and is expected to dissipate. The remainder of eastern Waikato and BOP are still experiencing some heavy showers and occasional thunderclap, but this is expected to clear during the evening.

Update as at 3.30pm 6 December 2012

The active line of showers and thunderstorms is expected to clear Auckland CBD by 3.30pm. Active thunderstorms are now moving into the Bay of Plenty and there are Watches and Warnings in place. The whole system is then expected to clear the North Island later this evening.

A different system is also expected to bring active showers and possible thunderstorms to Taranaki from late evening.

Severe Thunderstorm Outlook map issued at: 2:52pm Thursday 6 Dec 2012

Severe Thunderstorm Outlook map valid to Midnight Thursday 6 Dec 2012, issued at: 2:52pm Thursday 6 Dec 2012

Severe Thunderstorm Outlook map valid to Midnight Thursday 6 Dec 2012, issued at: 2:52pm Thursday 6 Dec 2012

We will update this blog again before 5pm. Further updates will then be available through Watches and Warnings, as well as on our Facebook page and on Twitter.

Where to find the latest information from MetService:

Latest Severe Thunderstorm Warnings here: http://metservice.com/national/warnings/severe-thunderstorm-warnings

Rain radar here: http://metservice.com/national/maps-rain-radar/rain-radar/all-new-zealand

Latest Severe Thunderstorm Watches here: http://metservice.com/national/warnings/severe-thunderstorm-watch

Latest Severe Thunderstorm Outlook here: http://metservice.com/national/warnings/severe-thunderstorm-outlook

Latest Severe Weather Warnings here: http://metservice.com/national/warnings/severe-weather-warnings

Latest Severe Weather Watches here: http://metservice.com/national/warnings/severe-weather-watch

Latest Severe Weather Outlook here: http://metservice.com/national/warnings/severe-weather-outlook

Check our Facebook page here: https://www.facebook.com/MetService

Follow @MetService on Twitter here: https://twitter.com/MetService

The science behind the new Auckland forecasts

We’ve added a lot more detail to the forecasts for Auckland on metservice.com.

In addition to the existing Auckland forecast on the Towns & Cities page, we’ve divided the greater Auckland region into five sub-regions – each with its own characteristic  rainfall, temperature and wind patterns:

To provide hourly predictions of air temperature, wind speed and rainfall for these sub-regions, we’re using

  • Data from our own localised-for-New-Zealand weather modelling and statistical processing systems (for more about this, see the blog on MetService’s Investment in Forecasting)
  • Observations of temperature and wind speed from representative weather stations within each of the sub-regions (see next point), which we’re blending with  the modelled data for the first few hours of the forecast.
  • The weather stations we’re using are Whangaparaoa (for North Shore), Whenuapai (for Waitakere), Auckland Airport (for Manukau), and Ardmore (for Hunua). For Auckland City we’ve created a “virtual weather station” near the Newton Interchange; this will do the job for now, but we want to replace it with a real station within Auckland City soon.

 Auckland Central forecast page screenshot

The index map at the bottom left of the map area links back to the Auckland Towns & Cities page you’re already familiar with, containing the overall Auckland urban forecast and max/min temperatures for the next 10 days.

This initiative was partly motivated by the great feedback we received about the ‘dust graphs’ of wind speed and rainfall added to the Christchurch pages in February, to alert people to the potential dust nuisance in the areas affected by liquefaction and, more recently, demolition of large buildings.

As always, we’re looking forward to hearing what you think! Tweet @MetService or drop us an email at enquiries@metservice.com

Big Day Out – A Day of Two Parts

On Friday, Mount Smart stadium in Auckland’s Onehunga becomes once again the site for the Big Day Out – a whole day devoted to music and dancing.

MetService hopes that all involved in this year’s bash have fun, and as I look at the MetService data for the day I can see that the weather is likely to come in two parts.

Part One should be sunny and dry — as seen in the rain map below taken from the MetService site here showing the scene at 10 am as proceedings start.   A cold front is expected to wander over the Auckland area overnight and you can see the remains of it over Northland.  Since the winds following the front are forecast to come in from the southeast, this is likely to be a sunny dry clearance.  So during the early afternoon full sunshine can be expected and the air temperature is likely to rise to 24C.  If you are in the full sun it will feel 6 degrees warmer than that, so just add water to keep your cool.

10am Friday 15 January 2010

Twelve hours later, by 10 pm, weather conditions will have noticeably changed, as shown in the map below.   That cold front mentioned before is expected to stall in the area east of northern New Zealand and that will allow a family of small weak low pressure centres to form on the weather map.  Winds go clockwise around lows,  so the wind direction over Auckland is likely to switch and come from the southwest late in the day. The onshore wind and falling pressure will help to make the atmosphere more unstable, and set the scene for showers to form, especially around western parts of Auckland.   Temperatures are likely to drop to around 18C and the humidity is likely to noticeably increase.  The mosh pit may become moshier.

10pm Friday 15 January 2010

These weather maps get updated often so click here for the latest.

Bob McDavitt