Perth is expecting a maximum in the vicinity of 32°C this Friday, a mark it has reached only once previously so late in autumn, in records going back to 1876.

While it's not unprecedented for Perth to sweat through 30-degree days in May, days of 30°C or higher become very rare after the first week of the month, while days of 32°C or higher (in any May week) are equally unusual.

Prior to this Friday:

• Perth has reached 30°C or higher in May a total of 28 times.
• Perth has reached 30°C or higher in May just five times after the first week, with the most recent occurrence being yesterday (May 8, 2025, maximum 31.1°C).
• Perth has reached 32°C or higher in May just five times.
• Perth has reached 32°C or higher in May just once after the first week. That happened on May 12, 2018, when the maximum was 32.7°C.
• Perth’s hottest May temperature on record was May 1, 2002, when the mercury hit 34.3°C.
• Perth’s average May maximum is 22.4°C at the current site (records since 1993), so today’s top temperature should exceed that by around 9 to 10 degrees.

UPDATE at 2pm, AWST: Perth reached 33.8°C at 1:15pm, making today its second-warmest May day on record, and the warmest May day recorded beyond the first week of the month.

Why the late season heat?

If (or more likley when) the mercury reaches 30°C in Perth this Friday, it will be just the second time that there have been three days of 30°C or higher in May. Why now?

There are times when a basic synoptic chart is still the best weather explainer. As you can see on today’s chart, Australia's weather is being dominated by the large high pressure system centred near Adelaide.

Image: Synoptic chart for the Australian region for Friday, May 9, 2025.

Air is circulating anti-clockwise around the high, directing warm, dry air from the interior of the continent towards the west coast.

By Saturday, an influx of slightly cooler air from the south will moderate temperatures in Perth, bringing maximums back to the mid-20s.

But any significant moisture or polar air will stay well south of southwest WA, with Perth maximums again reaching the high 20s next week as the next high pressure system ushers in a new blanket of warm, dry air from the interior.

Image: Maximum temperatures for Western Australia on May 9, 2025, according to the ECMWF model.

Meanwhile Perth parks and gardens await the first soaking rains of autumn, as the city faces the prospect of its seventh consecutive month of below-average rainfall. 

To date this year, Perth has received just 41.4mm of rain. Its long-term average from January 1 to the end of May is 171.2mm.