The Met Office said the warm air brought a risk of lightning, hail, storms and flash flooding later on Tuesday and into Wednesday morning.
A Yellow "be aware" warning is in place from 17:00 until 18:00 on Wednesday.
The extent of the thunderstorms is uncertain, but some places could see over 30mm of rain in an hour.
Prestwick in Ayrshire had the day's highest recorded temperature at 29C, followed by nearby Auchnicruvie at 28C.
Shetland was one of the only places in Scotland not to enjoy the sunshine - with the weather largely cloudy with patchy rain and drizzle.
Aberdeen - which was sitting at around 19C at lunchtime - was hotter than Nairobi, Kenya.
Heavy, thundery showers are forecast for Tuesday night.
The adverse weather could cause disruption on Wednesday morning. Frequent lightning is expected to continue along with high temperatures of 22 or 23C in the afternoon.
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The star, whose hits include Orinoco Flow and Book of Days, famously creates complex vocal arrangements, in which her voice is layered hundreds of times.
She told the BBC that, when she first became famous in 1988, replicating those songs on stage "wouldn't really have been possible."
"But now it is very, very possible. You see wonderful concerts.
"There are orchestras there, choirs there, so it's a different time."
But, the star added: "I don't know if that's something I would do."
Enya is one of the most-successful folk singers of all time, selling more than 75 million records worldwide. Yet she has never played a solo concert, and tends to disappear for years between albums.
She said the decision not to tour with her music had initially arisen out of necessity.
"We actually had in my [record] contract that we would have two to three years between each album, " she said, explaining that the painstaking construction of her songs required several years of work.
"So that's why I ended up not touring. The success of [my debut album] Watermark caught them by surprise, as it did me. They were worried that if I went on tour and then had three years to work on the next album, it would be too much of a gap."
Enya admitted that, had she become famous in this decade, "the focus would have been to tour".
"A lot of artists now are touring because sales are not what they were in 1988."
And she will perform some of the material from her latest record, Dark Sky Island, on US television later this year, "because they insist".
The album is her first in seven years, and is preceded by a single - Echoes In Rain - which has been described as a companion piece to her breakthrough hit, Orinoco Flow.
A full interview with Enya will be published in coming weeks.
Temperatures topped 29C on Scotland's hottest day of the year so far - sparking a warning of overnight downpours and thunderstorms.
[NEXT_CONCEPT]
Irish folk singer Enya says it would be "very possible" to perform her songs on tour for the first time.