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NOAA: Seasonal average of tropical storms, hurricanes increased

Published: Apr. 13, 2021 at 6:12 PM EDT
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TALLAHASSEE, Fla. (WCTV) - It’s that once-a-decade event where a group of meteorologists crunch the numbers to determine what “normal” is.

With hurricanes, the new 30-year average isn’t something to celebrate. There has been an increase in tropical storms and hurricanes from the previous 30-year record NOAA announced Friday.

The average number of tropical storms per season increased from 12 with the 1981 to 2010 period to 14 during the 1991 to 2020 period. The amount of hurricanes increased from six to seven with no change in the number of major hurricanes.

This meteorologist analyzed older seasonal data to determine the 1971 to 2000 average. Seasonal numbers were pulled from annual hurricane season summaries posted on NOAA’s Atlantic Oceanographic and Meteorological Laboratory’s website. The older data, which also included subtropical systems, show that the seasonal average was 10 tropical storms and six hurricanes with two of those hurricanes classified as major. The last three seasonal “normals” indicate an upward trend in tropical cyclones in recent decades.

This is a chart showing the average annual number of (sub)tropical storms, hurricanes, and...
This is a chart showing the average annual number of (sub)tropical storms, hurricanes, and major hurricanes with each 30-year period.(Charles Roop / WCTV)

The new higher normal figures could be based on better observations in the last few decades, including satellite and hurricane hunters flying into tropical systems, NOAA said in their press release.

The government agency also cited the Atlantic remaining in a warmer multi-decadal phase since the mid 1990s known in the weather community as the Atlantic Multidecadal Oscillation. But a few researchers now believe that the AMO may not exist and the multi-decadal changes may be “an artifact of pulses of volcanic activity during the preindustrial era that project markedly onto the multidecadal (50- to 70-year) frequency band,” according to research published in a March issue of Science by Michael Mann and his coauthors (more details on Mann’s website).

As for climate change, there isn’t significant confidence on whether or not a warming planet is contributing to more tropical cyclones.

“NOAA scientists have evaluated the impacts of climate change on tropical cyclones and determined that it can influence storm intensity,” Matt Rosencrans, seasonal hurricane forecaster at NOAA’s Climate Prediction Center, said in the press release. Further research is needed to better understand and attribute the impacts of anthropogenic forcings and natural variability on tropical storm activity.”

It is likely that a warmer world will yield higher rainfall totals from tropical systems as well as higher intensities and a higher proportion of Category 4 and 5 hurricanes, according to researchers. There is also a high likelihood of sea level rise causing higher storm surge levels in the future.

While it’s not crystal clear yet why the Atlantic basin is seeing more storms, one thing is certain: More storms will be the new normal.

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