August Marks Start Of Hurricane Season's Annual Peak

The basin has gone quiet since Tropical Storm Colin dissipated near the coast of North Carolina on July 3. This recent downturn in activity is not unusual and is similar to last year, when no tropical storms roamed the Atlantic for more than a month between early July and early August.

Hurricane season runs from June through November, but most years, the first two months of the season are typically the calmest. June averages only one named storm every other year, and July has averaged one named storm per year since 1950.

August, September and early October are the peak times when it comes to the most tropical storms and hurricanes. You can see this depicted in the ramp-up of the white and red lines in the graph below.

It's also when some of the most powerful and destructive hurricanes occur. These hurricanes in the past five years all struck the U.S. during the peak of the season:

2021: Ida (Louisiana); Nicholas (Texas)

2020: Isaias (North Carolina); Laura (Louisiana); Sally (Florida/Alabama border); Delta (Louisiana)

2019: Dorian (North Carolina)

2017: Harvey (Texas); Irma (Florida); Maria (Puerto Rico); Nate (Louisiana, Mississippi)

Several factors contribute to the seasonal ramp-up that begins in August:

• African easterly waves are most developed, often serving as a seed for tropical storms and hurricanes to form.
• Saharan air layers – surges of dry air into the central and eastern Atlantic Basin that normally squelch tropical development in those areas – tend to give way by August as the parade of African easterly waves gradually add moisture. This opens up more favorable real estate for tropical cyclone development.
• Wind shear – the change in wind speed and/or direction with height, which can rip apart a tropical cyclone wannabe – tends to be low.
• Sea-surface temperatures rise toward a peak in early fall, providing more potential energy for a tropical cyclone.
• Instability – the atmosphere's ability to generate convection (thunderstorms) to help initiate tropical cyclones – also rises toward an early fall peak.

All of those factors make for a larger area in the Atlantic where tropical storms and hurricanes can develop, compared to June and July.

Of course, averages and climatology provide no guaranteed outcome in any individual hurricane season. The 2020 season was a great example, as U.S. hurricane landfalls spanned from as early as late July (Hanna) to as late as the end of October (Zeta).

However, if you have plans for, say, a Caribbean cruise, and you're concerned about hurricane season, the long-term data would suggest a lower chance of a hurricane interrupting your vacation in June or July, compared to August or September.

Then again, you might be able to nab a great discount on Caribbean travel in August or September. But make sure to buy travel insurance, just in case.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.