Police are urging motorists to drive to the conditions as fog blankets parts of the region each night.
Acting Senior Sergeant Nigel Hurley said people needed to be mindful of other motorists as visibility could be decreased on some roads.
The Hawke's Bay expressway has had patches smothered in fog in recent weeks, forcing drivers to decrease their speed and exercise extra caution.
Metservice meteorologist Emma Blades said fog was typical of high-pressure systems which had been providing the clear skies and cool nights.
She said it was slightly more unusual for Napier because it was close to the sea, and Hastings was more likely to experience fog because it was inland.
Mrs Blades said sheltered valleys and inland areas were more susceptible to fog.
She said this fog was known as radiation fog - "as the air cools it becomes cold enough to the point where it can't hold the moisture anymore and the water condenses".
"It's basically like being in a cloud on the ground. There's no difference between fog and clouds."
Likening foggy conditions to running a hot shower in a cool bathroom, she said the lack of wind flow in a high-pressure system stopped any mixing of air which meant fog lingered.
Yesterday the day peaked at 19C in Napier and 18C in Hastings.
Napier dipped to a low of 4C overnight while Hastings, being inland, stooped 3C cooler to a chilly 1C overnight.
Tonight in Hastings will be slightly warmer at 3C after a 18C day.
Napier residents will experience the same temperature but a warmer night, with 6C overnight.
Temperatures continue to climb to 20C in both Napier and Hastings tomorrow before a southerly cools temperatures and brings rain late afternoon.
A mild 9C is forecast for Sunday night in Napier, and Hastings will have one degree less at 8C.
Central Hawke's Bay has a similar forecast with a slightly cooler weekend at 15C both days, but a high-pressure system remains.
It is the third weekend of the month-long Hawke's Bay Winter F.A.W.C!, Food and Wine Classic with eight events jam-packed into Saturday and Sunday.
Many events take place inside, but the positive Hawke's Bay forecast helps showcase the best of the region to the number of outsiders who travel to the Bay for the event.
There were also seven events scheduled for Thursday and Friday, and next weekend 15 events will take place to round off the final weekend.