The thunder came on a day when Hawke's Bay was forecast to have among the highest temperatures in the country.
Just before 2.50pm, Hastings had the highest temperature among cities and towns at 28.8C, having a short while earlier peaked at 29.2C, according to the website of national weather agency MetService.
But heavy rain was reported just a few kilometres to the southwest in the vicinity of Roy's Hill and dark clouds were looming from the south.
A forecast for the region updated at 1.40pm said while conditions were expected to be mainly fine, it was also expected there would be "a few showers, mainly about the ranges and south of Hastings, some heavy", with possible "thunderstorms and downpours", and with northwesterlies.
MetService meteorologist Dan Corrigan told Hawke's Bay Today there had been "a fair bit of thunderstorm activity" in Central Hawke's Bay and there were "a couple of cells" just west of Napier and Hastings.
Weather in the coastal areas of Napier had gone from a near cloudless sky to some rain within about 10 minutes.
There could be some brief periods of heavy rain in some areas, Corrigan said. He expected a slight drop in temperatures as cloud passed over, but the forecast highs of over 30C could still be reached.