Ships have returned to Napier Port after swells lead to a four-day, unprecedented halt on vessels coming in to dock.

General manager of container operations Warren Young said large swells which hit the East Coast on Wednesday had dropped enough to start operations again.

"Swells are on the way down, so we are now operating under normal marine parameters which means we were able to bring two log vessels in.

"As always, we'll assess each subsequent move on conditions and vessel size."

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The closure did not affect landside operations.

Heavy fog on Saturday morning also caused disruptions for those flying in and out of Hawke's Bay Airport.

An Air New Zealand spokesperson said several flights were cancelled due to the weather.

MetService Metrologist Tom Adams said the fog was caused by a mass of warm air sitting over the region, which cools overnight.

"If there is no wind what happens is the ground cools down faster than the air above it.

"As the ground cools down faster than the air above it, it cools the bit of air which is directly above the ground faster than higher up."

Heavy swells which hit Hawke's Bay last week. Photo / Paul Taylor
Heavy swells which hit Hawke's Bay last week. Photo / Paul Taylor

This creates a layer of cold air near the surface, and the water in the air condenses, forming water droplets, causing fog.

Adams said wind clears the fog more quickly, as it mixes the cold, surface air with the warmer air above it dispersing it.

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"If you don't have the wind then you have to wait for the sun to basically warm that colder air up.

"If it's been a really cold night, then that layer of cold air near the surface will be thicker, and it will take the sun longer to burn through it."

Going forward, Adams said there may be a few more foggy mornings, but with the wind expected to pick up mid-week, they are likely to clear.

"Winds are gradually picking up.

"You're staying in the same humid air mass really until we get through to Wednesday night.

"In terms of winds, winds do pick up Tuesday night."

He said Monday would likely be fine, with cloud thickening on Tuesday with possible showers.

"The rain develops on Wednesday and it turns southerly and colder on Thursday."

By 11am it was still a struggle to see the ocean from the Ātea a Rangi Celestial Compass. Photo / Ian Cooper
By 11am it was still a struggle to see the ocean from the Ātea a Rangi Celestial Compass. Photo / Ian Cooper

"After that we are in a southwesterly flow, so actually things should improve on Friday for Hawke's Bay."

He said, while it was still quite far out, they are expecting to see an improving trend going into next weekend.

Temperatures are expected to be above average for this time of year, at least for the start of the week.

Monday will see a high of 15C, dropping to 5C overnight.

It is expected to reach 17C on Tuesday, dropping to 4C.

From Wednesday the temperatures will start to drop, reaching 14C with an overnight low of 2C, and Thursday will be 13C.