The Atlantic hurricane season is ahead of schedule

Atlantic hurricane season is coming ahead of schedule as oceans warm, according to a new study. Big North Atlantic storms form earlier in the year than earlier, and forecasters say that means coastal communities need to be on alert earlier, too.

Tropical storms that reach a certain magnitude are named by the World Meteorological Organization. And the first named storms to develop each year have occurred about five days earlier every decade since 1979, according to the study published today in the journal nature communication. Named storms making landfall in the US have come about two days earlier every decade since 1900.

That means communities that often find themselves in the path of these storms may need to prepare for hurricane season sooner than in the past. And officials might want to reconsider the timeframe they’ve set for the Atlantic hurricane season, which has officially started on January 1 every year since 1965.

“As a hurricane forecaster in my late 20s, I noticed that a very unusual preponderance of storms was developing before the start of hurricane season,” says Ryan Truchelut, lead author of the new study. Truchelut co-authored the paper and co-founded forecasting company WeatherTiger with his wife, physicist Erica Staehling.

The authors of the new study based their research on storm evolution on observational data from 1979 to 2020. They limited themselves to examining those four decades, because that’s how long there are satellites that help meteorologists see the evolution of more storms. They felt that including previous years may have led to a biased assessment of seasonal trends over time.

In the past, researchers have found it difficult to work with such limited data to link rising temperatures to a longer hurricane season. But the past decade has been quite remarkable for forecasters. The seventh straight year that a named storm formed before June 1 was 2021.

Higher sea surface temperatures are likely the driving force behind this unusually early tropical storm activity, Truchelut and his co-authors found. These higher temperatures are strongly linked to climate change, and hurricanes gain strength in warmer waters.

Temperatures in May are usually not warm enough to cause major hurricanes. But the public should still take precautions for earlier storms, even if they are weaker, Truchelut warns. Heavy rainfall from these storms can pose a significant threat even if the storm’s wind speeds do not exceed the required threshold (111 miles per hour) to be considered a major hurricane.

The National Weather Service (NWS) is already considering moving the first official day of the Atlantic hurricane season to May 15 instead of June 1. And while the date hasn’t officially shifted, some hurricane forecasting efforts have already shifted. Last year, the National Hurricane Center decided to start publishing Atlantic Tropical Weather Outlooks on May 15th. These are routine forecasts that typically don’t come out until June.

Also, “hurricane season doesn’t have a strict scientific definition,” says Truchelut The edge. “It’s purely a social construct.” In 1935, the US Weather Bureau, the predecessor of the NWS, designated the Atlantic Basin hurricane season as June 15 through November 15. In 1965, the dates were pushed back to June 1 through November 30 to capture 97 percent of storm activity in the region.

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