The swampy heat wave pummeling the New York City area is slowing everybody down — and high-speed traders are no exception.

High humidity is impeding radio transmissions Tuesday among three New Jersey data centers where U.S. stocks trade, according to a note Nasdaq Inc. sent customers. It’s taking about 8 microseconds longer to send information from Nasdaq’s facility in Carteret to the New York Stock Exchange data center in Mahwah, and an extra 2 microseconds to send data to Cboe Global Markets Inc.’s exchange in Secaucus.

Northern New Jersey is under an excessive heat warning Tuesday, with temperatures in Carteret exceeding 90 degrees Fahrenheit (32 degrees Celsius) and humidity around 60 percent.

A microsecond — or one-millionth of a second — means nothing to humans, but for computer-driven trading firms it’s practically an eternity in an era when transactions are often measured in billionths of a second. The good news for high-speed traders: U.S. markets shut three hours — 10.8 billion microseconds — early today before tomorrow’s July 4 holiday.

Read more about the latest gambit by the fastest traders to speed up