METSERVICE:

This watch affects people in the following weather forecast districts:
Northland, Auckland, Great Barrier Island, Coromandel Peninsula, Waikato, Bay Of Plenty,

A very unstable airmass lies over the upper North Island. The latest band of heavy showers and squally thunderstorms is expected to move onto Northland later this evening, move through the Auckland area about 4am and continue southeastward passing over the Coromandel Peninsula around 7am to lie over western Bay of Plenty by noon Saturday.

Some of the thunderstorms within this band may be SEVERE, are most likely to occur about northeastern coasts, but may extend right down into the Auckland City area as the band passes. These SEVERE thunderstorms have the potential to produce brief heavy rain, hail of 15-20+mm in diameter, squally wind gusts to 120+km/hr, and there is a risk of a damaging tornado, particularly between the eastern Northland Coast and northern Coromandel Peninsula.

These squally winds and possible small tornadoes may cause some structural damage, including damage to trees and power lines, and make driving hazardous. If any tornados occur, they will only affect very localised areas.

See below for the latest MAPS…

Should severe weather approach, or if you feel threatened, take shelter immediately.

Issued by: Paul Mallinson

Chart BELOW amended for introduction of risk of severe thunderstorms.

The next band of heavy showers and thunderstorms will move onto the west of the North Island this evening and cross the upper North Island overnight and Saturday morning.

There is a moderate risk of one or two thunderstorms becoming severe over northern Northland later this evening. These may produce brief heavy rain, hail of 10-15mm possible damaging wind gusts of 110+km/hr and a possible small tornado about the northeast coast. Then over the rest of Northland and northern Auckland and extending down into north Taranaki, there is a moderate risk of thunderstorms developing by the end of the period giving localised brief heavy rain, small hail, wind gusts to 90km/hr, and possible small tornados.

There is now a moderate risk of thunderstorms in northwest Marlborough for a few more hours this evening.

A low risk of thunderstorms extends across into Bay of Plenty and Taupo, and down into north Westland, as indicated on the chart.

No thunderstorms or significant convection expected elsewhere.