Undoubtedly, in the last 10 years or so, there has been an increase in hurricane headlines. Part of this is because of our own unconscious bias. The US went for about a decade without a landfalling hurricane, which is pretty much absurd, and now that the rate of American landfall is ticking up, it feels like it is happening all the time.

And of course, with alarm bells ringing on the increasing heat in the ocean, we are acutely aware that the hurricane season is longer than it ever used to be. Sure, there are more large hurricanes making landfall in the US recently, and the season has become longer over the last couple of decades, but this doesn’t fully translate the issue.

As I said, we had a long lull after Katrina, where the US was spared, so an uptick in landfalling storms was always going to seem worse than it had been in recent memory, even if it is more a correction to what is a normal landfall rate. I think the misperception, however, is that we are having a bunch of strong storms regularly arriving on US Shores, when that is not really the case.

One thing is true about tropical storms is that they are being infused with more moisture, and as a result are bringing more rain. Every storm you see now has a greater tendency to produce flash flooding. This is partly being seen in Debby, where parts of the Carolinas and Georgia have been inundated. Debby wasn’t a particularly strong storm, but she was sure a soaker.

This is where the longer season comes into play a bit. As we know, the transition seasons of spring and fall tend to have the most dramatic weather over the continental United States. The jet dives south and brings active cold and warm fronts that make life a bit more interesting for everyone. Historically, the hurricane season is most active in September, just when things get more interesting with subtropical weather, and these cold fronts usher remnant hurricanes off into the north Atlantic.

In August, the dog days of summer, there are no big jet troughs or cold fronts, and storms are left to dawdle. Debby has been such a danger because she’s not been forced offshore. Harvey was an August storm, and he had the same issue 7 years ago. Dawdling. Storms are carrying more moisture, and early season storms especially are less likely to be kept moving, and flash flooding is on the rise with tropical storms. Expect this trend to continue for the long term.