Perth is set to experience its hottest Christmas Day in six years with a sunny day and a top of 34 degrees Celsius expected.

If it does get to the forecast maximum, it will be the hottest Christmas since 2012, when 39.6C was recorded.

But it is the lead up to Christmas that's set to be a scorcher, with the temperature peaking on Saturday at 39C.

The Bureau of Meteorology has forecast the days on either side of Saturday to also hover in the mid-30s.

The high temperatures will be the result of a high pressure system in the Great Australian Bight and a trough down the West Coast pushing warm easterly winds over south-western parts of Western Australia.

Last Christmas was slightly cooler, with the mercury reaching 32.5C, during an unusually mild summer in Perth with not a single day over 38C recorded.

The beach will be a popular spot this Christmas. ( ABC News: Andrea Mayes )

Last summer the city also experienced its longest run of summer days below 35C in more than two decades, with the mild spell lasting 31 days.

But this summer is shaping up to be sizzler, with one day — December 14 — already topping 39C within the first two weeks of the season.

The Bureau's summer climate outlook suggested warmer than average days and nights were likely for almost all of Australia from December to February.

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Christmas around Australia

A warm and dry Christmas day is on the cards for most of Australia, with BOM's first forecast for the day showing only a slight chance of rain for the majority of the country.

A large high pressure system is likely to cover most of the continent on the big day, bringing temperatures in the high 20s and into the 30s to most capital cities.

However, northern parts of WA and the Northern Territory will experience much hotter conditions with temperatures in the mid-40's possible.

Perth Christmas weather snapshot Average maximum 32.1C — Mt Lawley site (1993 - ) Average minimum 17.0C — Mt Lawley site (1993 - ) Average sunshine hours 12.8 hrs — Airport site (1993 - ) Hottest Christmas Day max 42.0C in 1968 Lowest Christmas Day max 19.7C in 1945 Lowest Christmas Day min 10.2C in 1922 Chance of Christmas Day rain Approximately one year in nine Last time rain fell on Christmas Day 1991

Meanwhile, Tasmania is expecting mild temperatures with the chance of light rain in the west and some late drizzle in the east.

BOM said at this stage, the only significant rain on Christmas Day was likely to be through some parts of northern Queensland and the Northern Territory, where afternoon showers and storms are typical during the wet season.

Christmas Day forecast: