One of the ‘hottest summers on record’ with ‘freakishly’ high temperatures to drive triple-peak pollen explosion

“Long-term warming of the planet over the past several decades is also a contributor.”

Todd Crawford, vice president of meteorology at Atmospheric G2, added: “We expect the most anomalous summer heat to extend from the southern Rockies to the Great Lakes and Northeast.

“The idea that August will be the warmest of the three summer months, relative to normal, matches the climate model output and analogues as well, adding some confidence to the idea of a back-loaded summer.”

La Nina is the ‘kettle’ which is just about to hit the boil to turn the heat up on spring and summer, according to Jim Dale of British Weather Services.

Mr Dale, a US weather correspondent, said: “La Nina has got to rev-up properly before we see the effect it will have on the summer.

“It is the kettle which is just starting to get boiling, and if it does, a warm spring could be on the cards.

“What is very much more likely, given the overall pattern of warmer summers, is that we could be looking at heatwave conditions in the United States at times through the coming months.”