An unstable northwest flow will cover northern and central New Zealand during the second half of Saturday, with bands of rain, heavy showers and possible thunderstorms affecting many areas. There is a moderate risk of thunderstorms affecting northern and western parts of the North Island from Northland to Horowhenua, including western Bay of Plenty, during the afternoon and evening, and about eastern Bay of Plenty and northern Gisborne/Tairawhiti from late afternoon into the night. A low risk covers many other parts of the North Island, and also Marlborough, Tasman/Nelson, inland North Canterbury and Westland. The low risk continues about northern and western parts of the North Island at night. These thunderstorms will bring localised heavy rain of 10-25mm/h, and small hail. There is also a low risk of one or two thunderstorms late afternoon and evening about about inland parts of central and south Canterbury, eastern Central Otago, far western Dunedin, inland parts of Clutha and Southland, and southern Fiordland. Also, although not depicted on the chart, there is a low risk of a few thunderstorms at the Chatham Islands on Saturday evening. No other thunderstorms or significant convection expected over New Zealand during this period.