Apr 4, 2024 - Energy & Environment

Forecasters: "Extremely active" Atlantic hurricane season ahead

Average sea surface temperatures for North Atlantic Ocean Basin
Data: NOAA OIST v2.1 via Climate Reanalyzer, University of Maine; Note: Mean refers to 1982-2011; Chart: Simran Parwani/Axios

The Atlantic hurricane season is likely to be "extremely active," with 23 named storms, 11 hurricanes and 5 major hurricanes, a prominent forecast group said Thursday.

Why it matters: This is the highest number of hurricanes that a team of meteorologists from Colorado State University have issued in the 41 years they have produced such outlooks during April.

  • The previous highest hurricane forecast in an April outlook was for nine hurricanes, first made in 1995.

Driving the news: The outlook warns that a combination of record warm sea surface temperatures across the North Atlantic Ocean Basin, combined with a rapidly developing La Niña event in the tropical Pacific Ocean, may supercharge the season.

  • The CSU team is forecasting that out of the 23 named storms, 5 will become major hurricanes of Category 3 intensity or greater.
  • This compares to the 1991-2020 average of 14.4 named storms, 7.2 hurricanes and 3.2 major hurricanes.

Between the lines: La Niña events tend to reduce wind shear, occuring when winds blow in different directions and/or speeds with height, across the tropical Atlantic.

  • It can disrupt tropical storms and hurricanes, so its reduction would potentially give rise to increasingly intense storms.
  • The waters of the tropical Atlantic are record warm and have been at record levels for months.
  • Not only that, but unusually warm waters extends to deeper depths, making for record high ocean heat content that are more typical for June than early April.
  • This means that stronger trade winds, which could potentially cool Atlantic waters, would have less of an effect since they would simply draw more warm water to the surface.
hurricanes and sea temps
Atlantic sea surface temperatures in the "Main Development Region" since 1981. Credit: NOAA, Michael Lowry

Zoom in: To produce its outlook, the CSU team used a combination of a statistical model and simulations from medium-range computer model projections.

  • When it comes to ocean temperatures, meteorologists are especially interested in the temperatures of a particular rectangular region just west of Africa to east of the Lesser Antilles, where many Atlantic storms tend to develop.
  • According to Michael Lowry, hurricane specialist and storm surge expert at WPLG Local 10 in Miami, the average temperature in this area topped 79°F this week. That is "a threshold we wouldn't typically cross until July based on the current 1991-2020 climate period," he tells Axios.
  • Lowry is independent from the CSU group.
  • According to Lowry, this is "scary warmth" when combined with the developing La Niña. "It's a hard signal to ignore."

Threat level: Scientists don't have observations for an Atlantic hurricane season with the setup that the current one has, cautions meteorologist Brian McNoldy of the University of Miami (who also is independent of the CSU team).

  • In other words, we're in uncharted territory.
  • "An extremely aggressive seasonal forecast will come as no surprise given the anticipated conditions this summer," McNoldy told Axios in an email, citing the ocean temperatures and quickening shift from a strong El Niño to La Niña.
  • "We don't have a historic analog of a La Niña with Atlantic ocean temperatures this warm," he said.
  • According to the CSU group, there are greater than average odds of hurricane and major hurricane landfalls along the U.S. coastlines during the 2024 season.

Context: The reasons for the ultra-warm waters in the North Atlantic are not fully understood, though human-caused climate change is likely playing a significant role, scientists say.

Yes, but: All it takes is one significant storm to cause major damage, and forecasters have little skill in predicting areas most at risk so far in advance.

What's next: The CSU team will issue forecast updates on June 11, July 9 and Aug. 6.

  • Still to come later this month and during May are separate seasonal outlooks from the University of Pennsylvania, The Weather Channel and the official source, which is the NOAA.
  • Hurricane season officially starts on June 1, though there has been a recent trend toward named storms forming during May.
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