For many who are caught in, recovering from or trying to avoid the next heatwave, their prayers for rain might well be answered.

And then some.

The super hot temperatures in the U.S. and Europe this summer are expected to give way to the strongest El Niño cycle in 149 years, threatening cooler and wetter weather in the southern half of the United States, perhaps in time for back-to-school.

El Niños roll in periodically and last nine to 12 months as Pacific trade winds weaken and push warm water back toward the West Coast, coaxing the jet stream lower.

TD Cowen analysts hosted Bill Kirk, chief executive officer of Weather Trends International, for a recent weather update, translating what the almanac says for retail sales.