It’s one of the hottest days at the Australian Open in decades, with temperatures expected to reach mid-40 degrees Celsius on Tuesday, and the tournament’s official heat stress scale has reached 5 – its highest level, which results in ‘suspension of play’. This means all matches on outdoor courts must be halted, while play has been paused on the arena courts, including Rod Laver Arena, to close the roof.

The extreme heat has caused little disruption as organisers planned ahead with the schedule, placing very few matches on the outer courts. They each had one to two matches starting from 9am local time, which had already finished, and nothing else scheduled again until 6.30pm.

It means that no matches have been suspended entirely – but all practice on outer courts has been stopped. Over on Rod Laver Arena, organisers decided to close the roof after Aryna Sabalenka beat Iva Jovic, and before Alexander Zverev and Learner Tien took to the court, when the heat stress scale was still sitting at 4.7. The scale reached 5 just a few minutes later.

A doubles match on Margaret Court Arena, which saw Hailey Baptiste and Peyton Stearns face No. 4 seeds Elise Mertens and Zhang Shuai, was briefly halted after the first set so the roof could be closed at the same time, allowing the players to continue in air conditioning.

According to News.com.au, the Bureau of Meteorology’s forecast of 45 degrees Celsius makes this the hottest day in Melbourne since 2009. Temperatures will peak at roughly 5pm local time, but will still be in the 40s when the night session begins at 7pm.

The main showcourts are expected to be covered for the rest of the day, even heading into the night session, which features Elina Svitolina vs Coco Gauff, and Carlos Alcaraz vs Alex de Minaur. “Looking at the temperatures, I’m strongly believing that the roof will stay closed,” retired star Andrea Petkovic told viewers.

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The Australian Open has its own Extreme Heat Protocol, which takes air temperature, radiant heat, humidity, and wind speed into account. It also considers “the extent to which a person can control the rise in their body temperature and the physiological cost of doing so”.

These measures are expressed as the heat stress scale (HSS), something Tennis Australia implemented in 2019. The scale ranges from one to five, and cooling measures, breaks, and a full suspension in play can come into effect depending on the number on the scale. Heat stress scale readings are continually made throughout every day of the tournament.

The referee will continue to monitor the heat stress scale during any suspension of play to decide when it can resume. Players are then given at least 30 minutes’ notice of resumption of play.

Matches on outer courts were suspended for almost five hours on Saturday, when temperatures peaked at around 38 degrees Celsius. The final matches on the smaller courts are scheduled not before 6.30pm local time, but these could be pushed back if the scale remains at 5. The Australian Open also postponed the start of the wheelchair tournament to Wednesday in anticipation of the extreme temperatures.