The severest weather was expected east of Edgecumbe and down through Gisborne.
The MetService was expecting even bigger swells. Leigh Matheson, MetService metrologist, said south-easterly winds would strengthen in the Western Bay overnight and continue through this morning - gusting up to 100km/h.
Mrs Matheson estimated between 20mm and 30mm of rain would fall between tomorrow and Tuesday. It was expected to ease to showers in the afternoon when wind gusts would increase to 110km/h before easing.
However, massive swells of up to 7m were set to batter the coastline before easing to 3m this evening, she said.
Ships tied up at the Port of Tauranga had extra lines attached to handle the big seas, with ships crews and tug boat crews on standby overnight.
Jeff Maunder, the Fire Service's assistant commander for the Bay's coast, said they expected the impact of Cyclone Pam to be felt just after midnight.
"By the morning we should be well involved with aunty Pam."
He said it was a serious cyclone that had the potential to cause road slips and impact on other infrastructure. It meant that the Fire Service had deployed extra resources to Thames, the Coromandel and Whakatane to reinforce existing services.
"It is about which bits are going to get isolated," he said. Tauranga was well looked after and had enough staff.
Meanwhile, four Tauranga supermarkets have reported a busy weekend from customers stocking up on emergency essentials such as bottled water, candles and batteries.
Mount Maunganui New World duty manager James Lawson said they were a lot busier than normal yesterday. The influx was from people preparing for Cyclone Pam.
Brookfield New World duty manager Hayden Weidenbohm said they had particularly noticed customers stocking up on water.
A spokeswoman for Countdown Bethlehem said the last three days had been busy with people stocking up on emergency provisions including food. Bayfair Countdown said they had been really busy, with one staff member reporting a big demand for boxes of candles.
Tauranga Coastguard operations manager Simon Barker advised boat owners to make sure their vessels were well tied up and to keep an eye on the weather.
Be prepared for Cyclone Pam today
* Free sand bags are now available and can be picked up from the Phoenix car park in Mount Maunganui and at Downer Depo on Taurikura Drive in Tauriko.
* Sand bags in Tauriko are pre-filled but people are advised to bring a shovel if collecting sand bags from the Mount.
* Secure or move indoors any large heavy objects outside that could blow around in high winds, such as outdoor furniture and rubbish bins.
* Turn trampolines upside down. Lift valuable household items and chemicals as high above the floor as possible.
* Farmers should ensure equipment is stored safely and animals are in a safe place or moved to higher ground if necessary, away from power lines and potential landslides.
* Close windows, external and internal doors. Pull curtains and drapes over unprotected glass areas. Keep materials at hand for repairing windows, such as tarpaulins, boards and duct tape.
* Don't walk around outside.
* Power cuts are possible in severe weather. Unplug small appliances that may be affected by electrical power surges. If power is lost, unplug major appliances to reduce the power surge and possible damage when power is restored.
* Bring pets inside.
* The NZ Transport Agency advises motorists to avoid any non-essential travel during severe weather.
