More than 1000 lightning strikes across the Bay of Plenty region have been recorded since midnight.
Metservice weather forecaster Hordur Thordarson said the good news was the lightning should clear to make way for a high of 21 degrees today.
"There have been a lot of electrical storms out at sea in the Bay of Plenty," Thordarson said.
"Because of our current weather situation we have a lot of cold air up high but the sea is still warm from the summer.
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"Warm air is light and rises up which cause it to become unstable and that's what triggers these thunderstorms."
Yesterday Metservice meteorologist Amy Rossiter said reports of red and orange flashes could be attributed to the way the lightning was reacting to clouds or things in the atmosphere.
Last night police urged motorists to take extra care in lower Bay of Plenty areas on the route between Turangi and Tokoroa and the route from Taupō to Rotorua.
"The roads are extremely slippery following heavy hail in the area.
A MetService severe weather watch was in place for eastern parts of the North Island overnight on Sunday and during the day on Monday with heavy rain expected.
"A complex and slow-moving trough of low pressure affects the North Island until Monday night, bringing rain or showers to many places, with some heavy falls about eastern districts."