A lengthy burst of thunder in the Wellington region early on Sunday has been linked to a stream of warm air coming across the Tasman.
MetService said a heat wave in Australia sent a stream of highly-charged warm air across the sea which released electricity when it rose over coastal mountains here, forming what meteorologists call a wave cloud.
These clouds do not usually produce thunder, and no one in MetService can remember it happening in Wellington.
Forecasters said the continuous stream of this wave cloud explains why the thunder lasted so long.
Most thunderstorms occur within cumulo nimbus clouds caused by a single updraft and do not last as long.