Where Do U.S. Hurricanes Typically Form this Time of Year?

Monitoring a disturbance moving toward the islands of the eastern Caribbean this week

As we look across the wide expanse of the Atlantic during what is normally the most active part of the hurricane season, it’s helpful to know where to train our gaze for development, especially those areas historically prone to breeding U.S.-bound hurricanes.

Of the hurricanes that have struck the U.S. (both mainland U.S. and island territories) in the modern record (since 1950) from mid to late September, about 85 percent have formed in the traditional Main Development Region or MDR (the tropical Atlantic and Caribbean Sea between 9.5°N and 21.5°N) and over 60 percent in the MDR east of the Caribbean through the deep tropical Atlantic. Of the few that have formed outside the MDR and hit the U.S. as hurricanes, they’ve typically originated closer to Florida and the Bahamas in the lower reaches of the Sargasso Sea.

This isn’t, of course, to say every storm that forms in these locations is headed to the U.S. as a hurricane. To the contrary, only a select few that form (around one in five) eventually impact the U.S. as hurricanes. Understanding the climatology of U.S. hurricane formations, however, gives us a good starting place when the disturbances start bunching up this time of year.

Today, we’re following two disturbances squarely in the Atlantic’s Main Development Region. Neither disturbance – stormy ripples in the wind field moving through the deep tropics – pose any immediate concern for us, but we’ll want to monitor the westernmost disturbance this week as it charges westward toward the eastern Caribbean islands this week. It’ll face the usual cocktail of shear and dry air ahead, but since it’s not turning out immediately and will be approaching the islands by the end of the workweek, it’s worth an occasional check-in.

In the meantime, we’ll continue to enjoy a surprisingly underwhelming hurricane season so far in the Atlantic.