The NSW Rural Fire Service has declared a total fire ban for the Greater Sydney Region on Tuesday, September 19, as strong winds add an extra element of danger to the ongoing record-breaking September hot spell.

It’s not known whether this is the earliest Sydney total fire ban that has ever been enforced, however it's safe to say it's extremely unusual for this time of year.

• Sydney is forecast to reach 34°C on both Tuesday and Wednesday
• In data dating back to 1859, the city has only reached 34°C in September on three occasions (once each in 2000, 1980 and 1965)
• This would be its first pair of 34°C days on record for September

As of 9am, there are 61 fires burning around the state, with 13 not yet contained. Over 500 personnel are working to contain these fires. There is a TOBAN for the Greater Sydney Region and Far South Coast. More info on Hazards Near Me and #RFS website: https://t.co/SwFG8PzKTA pic.twitter.com/HOohQ1LLMQ

— NSW RFS (@NSWRFS) September 18, 2023

But temperature is just part of the equation...

It’s not just the remarkable early spring heat that has caused today’s fire ban in Sydney, even though Sydney has recorded top temps well above 30°C for at least three days now in virtually all suburbs, except a few coastal spots cooled by the sea breeze.

Wind and rainfall deficiency are also factors at play here.

Northwesterly winds will become gusty on both Tuesday afternoon and Wednesday. These are the scorching dry winds that typically fan east coast fires in summer.

You can see the big engines driving this system on the chart above. Hot air from the interior of Australia is being funnelled towards the NSW coast as it circulates around that large high pressure system centred in the Tasman Sea.

Meanwhile the low pressure system lurking well south of the Great Australian Bight in the Southern Ocean is playing a part too, strengthening winds in southern Australia as the cooler air moves east.

That's the wind side of things. As for rain, you can see on the graph below that Sydney has had a fraction of its average rainfall in four of the last five months.

There's a lot of bushland both in and around Sydney, and it is already very dry with smaller creeks reduced to a trickle.

We should mention that the Sydney ban is one of two total fire bans in NSW this Tuesday, with the second being the Far South Coast region.

Many more NSW regions are likely to see total fire bans on Wednesday as winds continue to strengthen ahead of a much-needed cool change in southern parts of the state.

Meanwhile the fire danger rating is now catastrophic on the NSW Far South Coast, while the Monaro Alpine Region has a high fire danger this Tuesday, even as Perisher remains open for skiing and snowboarding with several lifts running.

Weatherzone is trying to confirm whether there has ever been a high fire danger during the ski season before, or a rating so high for the South Coast in September, and we'll update this story if and when we know more.

TOTAL FIRE BANS: WHAT ARE THE RULES?

You can read more here at the NSW Rural Fire Service, including whether you can operate a gas BBQ outside and so on. But the key points are:

• A total fire ban means no fires out in the open. A total fire ban helps limit the potential of fires developing.
• During a total fire ban you cannot light, maintain or use a fire in the open, or to carry out any activity in the open that causes, or is likely to cause, a fire.
• General purpose hot works (such as welding, grinding or gas cutting or any activity that produces a spark or flame) are not to be done in the open.