A heavy rain ban was slowly moving over the Western Bay of Plenty on Monday and was expected to stick around during the week.
There was also a moderate thunderstorm risk for Tauranga and the Bay of Plenty, Clark said.
"That means there could be rainfall of 10mm-25mm an hour," she said. "There is also a risk of localised downpours which means 25mm-40mm could fall in some areas."
Clark said heavy downpours could cause flooding and rivers and streams to overflow.
The heavy rain was expected to ease today but downpours were expected to linger in the Western Bay of Plenty as the rain ban moved westward.
"It is looking to be worse for the Western Bay of Plenty than Eastern Bay of Plenty," she said.
The forecast for Friday was mainly sunny with light winds. Saturday and Sunday were expected to be cloudy with light winds and showers, Clark said.
Tauranga Airport manager Ray Dumble said the first three flights scheduled to depart from Tauranga to Auckland, Wellington, and Christchurch were cancelled yesterday due to the weather.