He said the important thing about this heavy rain watch is the combined risk of thunderstorms, especially this afternoon and early evening.
"Because of the possible presence of those thunderstorms there could be localised downpours if the thunderstorm forms over an area and hangs around for a little while. So that's the particularly risky part of this watch.
"There's a risk of localised flooding if we do get those localised downpours."
Bakker said at this stage they had just issued a watch, rather than a warning for the affected areas.
"There's a possibility that rainfall amounts may approach warning criteria in some areas. For the lower North Island there's a possibility of 50 to 70 millimetres in nine hours or so. That is very dependent on there being thunderstorms though.
"If we do expect it to get worse we will issue warnings, but at this stage we're not expecting it to get to those warning criteria."
Further north, the East Cape could also experience downpours this afternoon and evening thanks to a trough of low pressure.
The heaviest rain is expected in Bay of Plenty east of Opotiki, and Gisborne north of Tolaga Bay. A heavy rain watch has also been issued for these areas, however they're not expecting thunderstorms, which lowers the risk.
Bakker said the best thing people can do is stay up to date with the latest forecasts.
"Because this is a watch rather than a warning it means that people should be prepared, but it's not the higher level of risks associated with orange warnings for example."
In the South Island, rain in Westland and Buller has eased, and the heavy rain warning and watch issued for these areas has now been lifted.
