A chilling forecast map shows storm surge 40cm high will hammer the top east of the North Island.
The MetService map has been issued in preparation for Cyclone Gabrielle, which is just days away from its predicted impact on New Zealand.
The map shows where the sea surge will be highest - and it's bad news for areas already hit by coastal inundation.
"Here's a forecast map for storm surge early on Tuesday morning. Storm surge is the overall level the sea will rise above normal," MetService said on Twitter.
"This does NOT factor in waves, which will also be very large on top of this."
As the cyclone approaches swells will worsen with dangerous sea conditions predicted on Monday and Tuesday.
A MetService wave height map shows them building to as much as 7 metres from Sunday night onwards.
The Gisborne District Council urges anyone camping along the East Coast to pack up and leave their campsites as swells of up to six metres are predicted.
Meanwhile, Maritime NZ is strongly warning against boaties and recreational craft users being out when Cyclone Gabrielle hits.
"Our advice is simple, if this event continues how it is predicted, the water, whether inshore or offshore is no place to be," said general manager, regulatory operations Michael-Paul Abbott.
"If people are out offshore, our advice is to keep abreast of the forecast, and listen to the Coastal Radio Network Channel 16, which will provide updated MetService forecasts and warnings."
Harbourmasters issue warnings
Northland Regional Council Regional Harbourmaster Jim Lyle has warned recreational vessels to avoid going out to sea from Sunday to Wednesday.
"All vessels at anchor should seek a sheltered position and prepare for heavy winds. If possible, seek a marina berth or secure berth alongside," he said in a statement.
"Vessel owners should not leave their vessels unattended at anchor and should be prepared to run up the engines and motor against the wind if necessary to prevent dragging."
Lyle said by Saturday evening all mooring users should check their mooring headline is secure, that anti-chafe gear is in position, and the headline is not worn.
He urged people to keep a close eye on weather warnings as they came to hand over the weekend.
Auckland's Harbourmaster is also asking for mariners to take the weekend to get prepared for the arrival of Cyclone Gabrielle and check that their vessel is properly secured ahead of strong winds and potential storm surges.
And Gisborne Harbourmaster Peter Buell said all boats at anchor in the bay will be asked to leave by 10pm Monday until noon on Wednesday due to the high swells and wind.
