Today, September 10 is the statistical peak of hurricane season.
NOAA calculates the peak by looking at the number of storms per day in the last hundred years. And September 10th takes the prize with approximately 95 named storms. That’s almost one per year on this date. You would have about a 5% chance of NOT having a named storm in the Atlantic Basin on September 10th, according to this data.
And true to form, today, the Atlantic has two named storms, Lee and Margot, as I write this. However, neither is anywhere near the Caribbean or Gulf of Mexico.
NOAA hasn’t really been collecting hurricane data back 100 years. The chart above is based on 77 years of data, but “normalized” to 100 years to make the frame of reference more intuitive.
The 77-year period extends from 1944 to 2020, starting at the beginning of the aircraft reconnaissance era.
So Far This Year Vs. Average Season
Usually, by September 9, we’ve had eight named storms in the Atlantic Basin. That would be the H storm. However, this year, we’re already on the M storm. That puts us five storms ahead of the average year.
But wait! This year we also had a bonus storm in January. Only after re-analysis did the National Hurricane Center realize that it should have named the storm. But it didn’t. So, we’re really six storms ahead of the average season so far. And that’s far above the average.
The chart above is updated monthly and does not include the two named storms now in the Atlantic.
Forecast vs. Actual to Date
So, at the mid-point, how does this season compare to predictions? If the second half of the season is anything like the first, we could easily have more named storms and more major hurricanes than predicted by NOAA in its August 10 seasonal update.
Earlier this year, forecasters increased their predictions from a normal season to an above normal season. They predicted 14-21 named storms (winds of 39 mph or greater). We’ve already had 14.
Of those, NOAA said 6-11 could become hurricanes (winds of 74 mph or greater). We’ve had 4 so far (Don, Franklin, Idalia and Lee).
And of those, forecasters said 2-5 could become major hurricanes (winds of 111 mph or greater). We’ve had 3 of those so far (Franklin, Idalia and Lee). Franklin and Idalia reached Category 4 strength. Lee briefly exploded into a Cat 5.
Forecasters have linked storm intensity to sea surface temperatures. When average storms hit very warm waters, they can intensify quickly. And that is exactly what has happened this year.
Here’s a look at sea surface temperature anomalies (departure from normal) around the world.
Virtually everything between Africa and Houston is 1-3 degrees Celsius above normal (1.8 to 5.4 degrees Fahrenheit). Sea surface temperature data is current as of Sept. 9, 2023…just one day before the peak of hurricane season.
Posted by Bob Rehak on September 10, 2023 based on information from NHC.
2203 Days since Hurricane Harvey