On the back of a month of record high temperatures across WA, parts of Perth are sweltering in 40 degree heat this afternoon.

The mercury at Pearce ticked over 40.5 degrees Celsius about noon, while Perth temperatures peaked at a scorching 38.5C.

But, if you’re not a fan of the searing heat there’s relief in sight.

Temperatures across Perth have already started to drop as the Fremantle Doctor sets in for the afternoon and coastal areas are expected to see temperatures cool off for the rest of the day.

Tomorrow, the Bureau of Meteorology has forecast it to be 10C cooler in the city, while the clear blue skies will be tarnished by some cloud coverage.

Today’s scorcher follows a January of record heat for the State, with temperatures 2.3C hotter than usual.

Marble Bar residents struggled in 49.1C temperatures on January 13, while at the other end of the State, Red Rock Point also recorded a 49.1C day on January 23.

But, in what is testament to the extreme heat in northern and inland areas of WA, Perth has had a cooler than average start to the year.

While it reached 42.1C on January 20, the average temperature for the month was 30.5C - the coolest average temperature for January since 2007.

For Australia as a whole, January has been the hottest month on record.

The average temperature last month, averaged across the country, exceeded 30C for the first time ever for any month.

BOM senior climatologist Andrew Watkins said January's heat was unprecedented.

"We saw heatwave conditions affect large parts of the country through most of the month, with records broken for both duration and also individual daily extremes," Dr Watkins said in a statement on Thursday.

A high pressure in the Tasman Sea that blocked cold fronts and cooler air from reaching the country's south, and a delayed monsoon in the north, contributed to the heatwave.

"The warming trend which has seen Australian temperatures increase by more than 1 degree in the last 100 years also contributed to the unusually warm conditions," Dr Watkins said.

For NSW, ACT, Victoria and NT, it was the warmest January on record, while for the other states it was one of their warmest Januaries.

With AAP