"People need to take appropriate precautions," he said, noting that the current UV readings for Napier were at level 8 which is tagged as "dangerous".
A slow-moving high pressure system smothering much of the country is set to hang around for some time.
The sunshine and heat is forecast to continue through to next Monday when the temperature is expected to nudge a withering 34C.
It will hit 30C on Wednesday and Thursday, then start edging up to 33C on Friday, then "drop" to 30C on Mission concert day, then up to 33C on Sunday.
Hawke's Bay District Health Board public health medicine specialist Rachel Eyre said at outdoor concerts, in hot weather, it is even more important than ever to drink plenty of water and avoid or limit alcohol to prevent dehydration.
"Both the heat and alcohol are dehydrating, and the combination of both in this extremely hot weather can be dangerous. If you are drinking alcohol, remember the one-for-one message: for every glass of alcohol, drink a glass of water," Eyre said.
"Stay in the shade if you can - although that can be hard at outdoor concerts. Wear a hat, use sunscreen regularly, and keep an eye on your friends to make sure they are not becoming dehydrated."
So what does the presently computer generated long-range forecast hold for Elton's opening concert on Waitangi Day?
"At this stage it's not showing too many signals — it looks pretty settled," James said.
So, for Buble's day out it will be hot, and his performance will also generate plenty of heat, for as sales and ticket demands have shown the Canadian/Italian singer and songwriter is far from being an opening act for what is set to follow in the form of Elton John on February 6 and 15.
Buble is a genuine star, and a big-selling one in this neck of the world woods with more than 350,000 album sales.
He has rolled out three number 1 albums and seven top five albums and his Mission concert, which will be his only New Zealand outing, arrives while his latest album has again touched the Kiwi hearts — it has been declared gold.
On the global front he has sold more than 600 million albums and has picked up four Grammy Awards.
The 44-year-old, who last played in New Zealand seven years ago, is promising to make the "Evening with Michael Buble" a memorable one, and if recent reviews are anything to go by there is no doubt that will be the case.
The Guardian UK gave him five stars, while the Dallas Observer remarked "his lustrous lyrical baritone, as affable and magnetic as his punchy, droll personality, was in fine form throughout".
He is bringing quite a show — the 36-piece orchestra which will arrive with him underlines that.
And he has promised a "great show" — a "killer show" for his great hillside audience at a venue he has clearly heard about.
"The fabulous Mission Estate Winery" was how he put it.
The announcement of his concert was something of a stunner, as it came in the wake of Elton John being announced as the February 6 concert star.
That as then extended to a second Elton outing set for February 15 as ticket sales went ballistic...and both concerts are 25,000 ticket sell-outs.
As was the Phil Collins concert in February last year.
Any doubts about the Mission's ability to draw great artists and great crowds has been well and truly put to bed.
And one major ingredient for Saturday's concert, which went missing last year with Collins, is, as noted earlier, the weather.
There were slips and slides and several resulting injuries, at the Collins concert as showers swept across the Bay during the day, and into the evening to the bemusement of Collins who told the crowd he thought he'd left the rain back in England.
But rain is nowhere in the picture and it will not be too surprising if Buble requests more than just an occasional glass of chilled water as the heat descends.
On the request front, Elton John had initially asked that no photos be taken of his audiences but has since put that aside, while several other Mission performers, including Rod Stewart, had asked that media get their close stage shots done and dusted within the first three numbers.
Unlike when the Hollies played at Black Barn three years ago, and asked that no dancing be allowed until after the interval, when they played the Mission back in 2001 there were no such instructions.
Which may have been wise as the opening act Lulu stole the show.
Apart from Julio Iglesias (given what he delivered) nothing has hindered dancing on the hillside.
There had been suggestions Iglesias had at one stage said to one of his band "this crowd is boring" as the audience rustled and fidgeted during his low-key set.
There had been similar rusting and fidgeting at times during Cliff Richard's concert in 2003 with shouts of "play one of your songs" emerging as he rolled out covers of other songs — the performance had the tag the "Wanted Tour" — songs he would have wanted to have sung.
An old tradition of earlier Mission concerts had been to produce a specially labelled wine for the event, which in 2007 did not impress Eric Clapton at all as he was a recovering alcoholic on a strong sobriety road when he spotted the special red "Eric Clapton" wine.
They were removed from sale, and the show went on, although many agreed his performance came across slightly flat.
And while most acts put on 90-minute and sometimes more appearances the legendary Ray Charles chose to play a one-hour set back in 1994 and call it quits.
It took the crowd a while to realise that Charles, who did spark, had left the stage and that was that.
Mr Buble will be out there, in the summer warmth, for way much longer than that on Saturday.