Heavy fog clears into a beautiful warm day for Sydney thanks to northwesterly winds

The city awoke under a shroud of thick smoke, causing traffic chaos from the CBD to the west.

All ferries were cancelled, and the airport experienced cancellations and disruptions to dozens of flights.

Those disruptions caused knock-on effects to Brisbane and other airports across the country.

A cruise ship, stuck due to poor visibility, spent the morning honking to alert other boats on the harbour, waking up disgruntled Sydneysiders in the process.

"Who needs an alarm when you have an incessant ship", wrote one Twitter user.

"That cruise ship doesn't sound too happy #earlyalarmclock", said another.  

But as the sun rose, the fog started to disappear, leaving in its wake a beautiful sunny, unseasonably warm, day.

Weatherzone says the next two days in Sydney will see the city climb within two degrees of the city’s July maximum temperature record. It’s headed for a top of 24 today and 23 tomorrow.

26.5 degrees was recorded in 2017, which is the highest its been in 159 years.

The average for this time of year is 16.

A stream of northwesterly winds ahead of an approaching front will carry warm air from central Australia across NSW for the next 48 hours.

Cooler air will arrive and bring Sydney back from its summer holiday on Friday, pegging maximum temperatures back in the teens for the weekend.