NZ Weather Forum

Heavy Rain Warning - Orange
Impact: Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.

Area: Northland
Period: 21hrs from noon Sun, 20 Mar - 9am Mon, 21 Mar
Forecast: Expect 100 to 140 mm of rain to accumulate, mainly in the north and east, though some localised areas may see larger accumulations. Peak rates of 15 to 25mm/h, but localised areas of torrential rain of 25 to 50mm/h are likely in thunderstorms.

Area: Auckland including Great Barrier Island
Period: 16hrs from 10pm Sun, 20 Mar - 2pm Mon, 21 Mar
Forecast: Expect 80 to 110 mm of rain to accumulate, especially north of the Harbour Bridge, though some localised areas may see larger accumulations. Peak rates of 15 to 25mm/h, but localised areas of torrential rain of 25 to 50mm/h are likely in thunderstorms.

Area: Coromandel Peninsula
Period: 12hrs from 6am - 6pm Mon, 21 Mar
Forecast: Expect 80 to 120 mm of rain to accumulate. Peak rates of 15 to 25 mm/h but 25 to 40 mm/h in the north, especially in thunderstorms.

Area: Bay of Plenty west of Opotiki
Period: 13hrs from 11am Mon, 21 Mar - midnight Mon, 21 Mar
Forecast: Expect 80 to 110 mm of rain to accumulate. Peak rates of 15 to 30 mm/h, especially in thunderstorms. Another period of heavy rain is likely on Tuesday and an associated Watch or Warning will be issued closer to the time.

The frontal system continues moving south over the upper North Island overnight Sunday and Monday morning.

There is an associated moderate risk of thunderstorms for Northland overnight Sunday and into early Monday morning, and for Auckland and the Coromandel Peninsula overnight Sunday and during Monday morning. These thunderstorms are expected to bring heavy rain with intensities of 15 to 25 mm/h, and strong winds gusting 80 to 110 km/h. Additionally some of these thunderstorms could become SEVERE, producing localised downpours of 25 to 40 mm/h, as well as localised torrential rain with intensities greater than 40 mm/h. There is also a risk of a localised tornado occurring.

Downpours and torrential rain can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips. Driving conditions could be hazardous with surface flooding and poor visibility in heavy rain. While possible tornadoes may cause some structural damage, including damage to trees and power lines, and make driving hazardous. If any tornadoes occur, they will only affect very localised areas.

A lower risk of thunderstorms extends to the western Bay of Plenty, Waikato and Taranaki,

No thunderstorms or significant convection expected in other areas of New Zealand during this period.

Metservice wrote:Area: Rodney, Gulf, Kaipara, Auckland City, Waitakere, Franklin, Albany

Forecast: At 08:30 am, MetService weather radar detected a line of severe thunderstorms lying from HEN AND CHICKEN ISLANDS to WARKWORTH to PIHA.

This line of severe thunderstorms is moving towards the eastsoutheast, and is expected to lie from HEN AND CHICKEN ISLANDS to AUCKLAND at 09:00 am and from MOKOHINAU ISLANDS to OUTER HAURAKI GULF to MANUKAU at 09:30 am.

These thunderstorms are expected to be accompanied by torrential rain.

Torrential rain can cause surface and/or flash flooding about streams, gullies and urban areas, and make driving conditions extremely hazardous.

A Severe Thunderstorm Watch remains in force for AUCKLAND, GREAT BARRIER ISLAND, COROMANDEL PENINSULA and WAIKATO.

The National Emergency Management Agency advises that as storms approach you should:
- Take shelter, preferably indoors away from windows;
- Avoid sheltering under trees, if outside;
- Get back to land, if outdoors on the water;
- Move cars under cover or away from trees;
- Secure any loose objects around your property;
- Check that drains and gutters are clear;
- Be ready to slow down or stop, if driving.
During and after the storm, you should also:
- Beware of fallen trees and power lines;
- Avoid streams and drains as you may be swept away in flash flooding.

Issued: 8:34am Mon, 21 Mar
Next update: 9:30am Mon, 21 Mar

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