Perth warned of staggering heat on Christmas Day as temperature expected to reach 35 degrees in city

A cool change is coming to Perth, but festive revellers have been warned about a muggy Christmas Day, with a huge variation in temperature across the city.

While the mercury will hit 36 degrees on Christmas Eve, the Bureau of Meteorology expects conditions for Christmas Day to reach 35 degrees in the city.

But while a trough will bring cool changes to coastal areas in the mid-morning, the Bureau advised those further east to brace for Christmas Day in the high 30s, with an extreme fire danger in the Perth Hills.

A sharp increase in humidity is also expected to leave Perth with a sticky Christmas, before a cool change comes through on Boxing Day, with temperatures dropping to a maximum of just 25 degrees before a slow increase over the week to 31 again on Saturday.

The forecast comes as families prepare to indulge over the festive break, with crayfish being sold off the back of boats at Hillarys Boat Harbour on Saturday.