Yesterday was another steamer with 87 per cent relative humidity recorded at Cessnock.

Night-time offered no relief for the weather-weary, with readings in the 90s between midnight and 8.30am yesterday in Newcastle and Lake Macquarie.

The build-up has been coming for weeks with highs of up to 98 per cent recorded in the Lower Hunter for the first nine days of February.

In January, relative humidity peaked at 100 per cent in Nelson Bay.

Bureau of Meteorology Williamtown observer Alison Skinn said yesterday showers and thunderstorms were contributing to the humidity.

Cyclone Olga and a high pressure in the Tasman Sea were also having an effect.

"The southern Tasman Sea is directing easterly on-shore winds onto the coast," Miss Skinn said. "All that hot, moist air is coming off the ocean.

"The high humidity is going to affect people's thermal comfort. Certainly when you perspire, and all that cooling doesn't work so well when it's humid outside."

The warm and damp conditions are expected to persist.