Source: NZ MetService  Link below.

Valid to: Midnight Tuesday 15 May 2012
Issued at: 8:43am Tuesday 15 May 2012

An unstable westerly flow covers northern and central New Zealand today,bringing further heavy squally showers to western areas, including Buller and northwest Nelson, accompanied by small hail. There is a low to moderate risk of isolated thunderstorms for these areas, including Bay of Plenty, as indicated on the chart. Any thunderstorms that eventuate here are likely to produce localised heavy rain up to 15mm per hour, hail around 10mm in diameter, and also strong wind gusts of 90 to 110 km/h from Taranaki northwards.

Meanwhile a colder south to southwest flow spreads over southern New Zealand today, with lowering snow levels. Some heavy showers and small hail are possible about coastal Fiordland, Southland and Clutha today and for coastal Canterbury, the Kaikoura Coast and coastal Wairarapa from afternoon, with a generally low risk of isolated thunderstorms for these areas.

No thunderstorms or significant convection expected elsewhere.




http://www.metservice.com/national/warnings/severe-thunderstorm-outlook