Why August Marks the Beginning of What Is Typically the Busiest Part of Hurricane Season

The Atlantic hurricane season runs from June through November, but most years, the first two months of the season are typically benign. June averages only one named storm every other year, and July has averaged one named storm per year since 1950. This year has been an exception with seven tropical storms already forming by July 22.

But usually, August, September and early October are the peak months 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 three years all struck during the peak of the season.

2019: Hurricane Dorian (Aug. 24-Sept. 7)

2018: Hurricane Florence (Aug. 31-Sept. 17); Hurricane Michael (Oct. 7-11)

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 effectively 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.
• 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 when compared to June and July.

Of course, averages and climatology are no guarantee of an outcome in any individual hurricane season.

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.