After the hottest summer on record, where will September rank in the history books?
Let's see what the prediction markets, sponsored by Kalshi, are saying about where September will rank among the hottest months on record.
FILE VIDEO: Potomac River sets record temperature during blistering heat wave, contributing to large fish kill
The East Coast's Fourth of July heat wave drove the Potomac River north of Little Falls, Maryland, to a record temperature, contributing to a large fish kill, officials said. The Maryland Department of the Environment said one of its biologists recorded a water temperature of 94 degrees on July 4, while data from the USGS shows water temperatures peaking at 98.4 degrees.
The U.S. experienced its hottest summer on record in 2026. Now, as September enters its final act, where will the month rank in the history books?
September has cooled slightly, but it's towing a close line towards being the hottest on record around the world.
People cool off at fountains in Madrid Rio district in the Spanish capital during a heat wave, on September 6, 2026. (Oscar DEL POZO / AFP via Getty Images / Getty Images)
Global temperatures remain on pace to make September one of the warmest ever measured, despite tracking about 0.2 degrees Fahrenheit below the record set in September 2023, according to the Copernicus Climate Change Service.
The five hottest Septembers on record were 2023 at 61.5°F, 2024 at 61.1°F, 2025 at 61.0°F, 2020 at roughly 60.7°F and 2019 at roughly 60.6°F, according to Copernicus’ ERA5 dataset.
If September 2026 finishes near its current projection of about 61.3°F, it would rank as the second-hottest September on record, behind 2023.
Beachgoers watch the sunset at La Jolla's Windansea Beach on September 4, 2026 in San Diego, CA. (Kevin Carter/Getty Images / Getty Images)
The summer of 2026 tied 2024 as the hottest summer ever recorded globally, according to the Copernicus Climate Change Service, but the U.S. experienced its hottest summer on record.
Let’s examine how prediction markets are assessing whether summer 2026 was the hottest on record globally.
If current projections hold, September 2026 would rank as the second-hottest September on record, behind 2023, according to a live Copernicus ERA5-based temperature tracker.
The final outcome will be determined by NOAA’s National Centers for Environmental Information, or NCEI, after September ends and the agency releases its monthly global temperature analysis.