Tracking the Tropics: How accurate are hurricane season forecasts?

TAMPA, Fla. (WFLA) — The second week of the 2021 hurricane season is underway and the National Hurricane Center is already monitoring another area for possible tropical development.

The area currently being watched is in the southwestern Caribbean Sea near Central America. The NHC has dropped the chance for development down to 10% over the next five days and says “significant development of this system appears unlikely,” however, it will bring torrential flooding rains to northern Colombia, Panama, Costa Rica and Nicaragua.

Long-range forecast models that go out 10 days continue to forecast a system somewhere in the Gulf of Mexico. However, these longer-range models are much lower in accuracy, especially 10 days out, so that’s something to check back in on but not something to worry about.

The next named storm to develop will be given the name Bill. The first named storm, Ana, already formed northeast of Bermuda before the season began.

Experts are predicting another year of above-normal tropical activity, but what exactly does that mean?

Pre-Season Forecasts

Every year, both the National Oceanic and Atmospheric Administration (NOAA along with the National Hurricane Center) and Colorado State University publish a pre-hurricane season forecast that gives an idea if the season will be below normal, near normal or above normal, strictly in terms of number of named storms.

They both look at larger atmospheric circulation patterns, water temperatures, the African Monsoon and several other longer-range models that go out several months in time.

Colorado State’s forecast goes into great detail about the number of storms, the number of storm days there could be, how much energy the storms will accumulate and even the chance of landfalling systems.

CSU talks about how their forecasts can better predict the upcoming season with moderate accuracy compared to just looking at history and comparing this year to previous years.

NOAA’s forecast doesn’t give too many details besides a range of possible number of named storms, hurricanes and major hurricanes.

They both stress that these forecasts do not predict where any particular storms will develop or travel toward and that it just takes one strong storm to impact one area to make it a bad year for them.

How accurate are they?

The Tracking the Tropics team looked back at the past 11 years of data to question just how accurate these early season forecasts have been, strictly looking at the number of storms that actually developed compared to how many were predicted.

Turns out, the preseason forecasts do a relatively great job.

Taking an average of the season’s number of storms, hurricanes and major hurricanes when compared to the forecast, NOAA was off by 2.47 storms in the last 11 years, from 2010 to 2020. Colorado State was off by an average of 3.33 storms for that same period.

Even though both forecasts called for an above average season in 2020, due to the record-breaking number of storms, it did bring down each of the scores.

When omitting the year 2020 and just looking at the average number of storms each were off by from 2010 to 2019, the scores improved to 1.97 storms for NOAA and 2.9 storms for CSU.

Tracking the Tropics is back again this year to bring viewers across the country the latest updates to keep them safe and informed throughout hurricane season. We will stream every Wednesday at 2 p.m. ET with some of the nation’s top meteorologists from across the country and will have additional coverage of any named storms that develop in the Atlantic basin.

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