The answer emerges from global phenomena. Radiation from the sun falls unequally on our tilted, spinning planet, hitting with most impact at the Equator. There, the hot air rises into the atmosphere and power tropical cyclones through evaporation and the Coriolis effect, the spin created by the Earth’s curvature.

Tropical cyclones in the Atlantic — hurricanes — are most likely to occur after surface temperatures peak and large amounts of moisture are already in the atmosphere. That season lasts from June to November, with the most perilous period from mid-August to mid-October.

Tropical cyclones in the northwestern Pacific — typhoons — can form year-round because of warmer waters, but they most commonly occur from May to October.

And global warming has increased the amount of energy absorbed by oceans, which scientists believe has resulted in stronger storms.

That’s it for this briefing. And sorry, another correction. Tuesday’s Back Story misspelled the surname of Alan Siegel, the brand consultant who devised the N.B.A.’s logo. — Alisha

Thank you

To Mark Josephson and Eleanor Stanford for the break from the news. Will Dudding, an assistant in the Standards Department, wrote today’s Back Story. You can reach the team at briefing@nytimes.com.

P.S.

• We’re listening to “The Daily.” Our latest episode is about the collapse of talks between the U.S. and the Taliban.

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• On Thursday, our columnist Andrew Ross Sorkin will interview the president of Microsoft, Brad Smith, and the U.S. Treasury secretary, Steven Mnuchin, in Washington D.C. The interviews will be livestreamed on DealBook’s Twitter page.