Sydney will likely come close to notching its hottest day this late in the summer for 12 years - and there won't be much early relief.

May and autumn will come close to being a record warm ones for Sydney, the state and the rest of Australia as the giant El Nino added a hot overlay to temperatures that are rising in the background here and in most parts of the world.

Enjoy the sunshine at the start of this week, as the the grey clouds and rain that have become all-too-familiar visitors in recent times are due to roll in again come Wednesday.

Sydney may be scorching right now, but be warned - the worst is yet to come.

Coogee Beach looked like a construction site - or a popular holiday destination for heavy machinery - as 12 large earth movers, two vacuum trucks and a crew of 35 worked to restore the beach to its pre-storm glory.

A high-pressure system "as big as Australia" could bring Sydney's warmest patch of weather since April, while most of the country will go for a week with little rain.

Unprecedented rain in Japan unleashed heavy floods that tore houses from their foundations, uprooted trees and forced thousands from their homes.

They said it would never fill. Now it has spilled.

A powerful cold front is set to bring 'dangerous' conditions to large parts of south-eastern Australia in coming days and send temperatures plummeting in Sydney.

Sydney's late-summer spell of unusual warmth shows little sign of making way for autumn with another week of mild to hot weather ahead.

Sydney awoke to a frigid Saturday morning, with temperatures dipping to a brisk 7.3 degrees in the CBD at 7:15am.

Electricity demand surged to its highest in Sydney and the rest of the state for the summer as a burst of inland heat sent the mercury into the low 40s in the city's west.

Melbourne could be hit with floods this week as recent rainfall puts pressure on catchments at capacity.

Sydney sweated through its hottest December night in 15 years overnight, but a cool change - and a good drenching - is on its way.

Three days of heavy rain in mid-April were enough to make it Sydney's wettest autumn in 12 years but conditions have largely dried up since.