Stormy Christmas for eastern South Island

Flash flooding is possible in low-lying areas. Photo / Thinkstock

Severe thunderstorms and hail are forecast for the east of the South Island today.

MetService forecaster Paul Mallinson said strong daytime heat would combine with moisture and wind to raise a moderate risk of severe thunderstorms from northeast Otago to north Canterbury.

The storms are predicted to be very slow-moving with rainfall of 25-40mm an hour and 5-15mm of hail.

That could lead to flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips.

Driving conditions will be hazardous with surface flooding and poor visibility in heavy rain.

Heavy showers and thunderstorms are expected to ease in the late evening.