Thousands of Britons braved rainy weather and grey skies over London to witness the coronation pomp and pageantry.
The Met Office said many southern parts of the UK are likely to be cloudy with some outbreaks of rain throughout Saturday afternoon.
This has raised fears a planned military flypast of more than 60 aircraft over Buckingham Palace at 2.30pm on Saturday could be called off.
On Saturday afternoon the Royal Air Force tweeted: “For the #Coronation of Their Majesties The King and Queen, the UK Armed Forces will conduct a flypast over Buckingham Palace, subject to weather, serviceability, & operational commitments.”
But the Met Office said temperatures could “could get to 22C in the South East” on Sunday.
This would be the highest temperature recorded in the UK in 2023 so far, exceeding the 21.2C in Kinlochewe, Scotland, on April 17.
On Saturday, Met Office meteorologist Marco Petagna told the PA news agency it is “definitely wet weather gear” weather, adding “It’s not going to be very nice this afternoon.
“A lot of standing water around, puddles. Things could be a lot better, to be honest, not looking nice at all.”
He said Saturday’s conditions were “certainly good for reservoirs” but “not particularly good if you are doing events out and about as many people are”.
Mr Petagna added: “For the South East it’s not looking great to be honest from now onwards through the day we are going to see cloudy skies, outbreaks of rain.
“So across the South East, some of the rain could be on the heavy side turning a bit more showery into the afternoon.”
He said temperatures in the capital could peak at 16C or 17C on Saturday afternoon, with 17C expected in Belfast and 15C in Glasgow.
Mr Petagna stressed that it was not his place to decide whether the conditions were appropriate for the military flypast.
But he added: “There’s going to be low cloud around so it’s not going to be the of best conditions. Certainly not good conditions for flying.”
Aircraft from the Royal Navy, British Army and Royal Air Force are set to take part in the display.
Elsewhere on Saturday, he said north-east England and eastern parts of Scotland could see some low cloud, with some brighter spells developing in places such as Northern Ireland and western Scotland.
He added: “Some brighter skies also a scatter of heavy showers and one or two of the showers could be thundery, so, essentially, cloudy and wet across central and south-east England.
“Elsewhere brighter later with some showers.”
On Sunday, he said, Britons can expect “a bit more of an east/west split” of weather conditions.
He added: “In the east tomorrow we will see further heavy showers, particularly across eastern England whereas out towards the west it’s drier and brighter and a bit warmer tomorrow as well, temperatures tomorrow could get to 22C in the South East.
“That would make it the warmest day of the year so far.”
He said these highs could be enjoyed in “the London area”.
He added: “Wet and fairly windy weather moving across from the west, sweeping eastwards across all areas Sunday night into Monday.
“Followed by sunshine and showers in the west late on Monday.
“It’s going to vary day to day.
“This (Saturday) afternoon the showers could be particularly heavy across the west of Northern Ireland, southern Scotland and later parts of the Midlands as well could see some quite heavy showers.
“Whereas tomorrow, it’s more east and south-east England and then on Monday the rain coming in will be heaviest on hills in the west and north west.”
He said areas in south-east England and potentially in Northern Ireland could get highs of 18C or 19C on Monday.