As the Atlantic hurricane season continues, there are questions arising about whether activity is behind schedule. My answer is, “Not really,” but it depends on how you look at it. As the Atlantic basin shows signs of life in coming weeks, here’s a breakdown of what we typically expect as we enter August, and why there may be a perception of a “slow” start.
I was prompted to write these thoughts after seeing assertions that the Atlantic hurricane season is off to a slow start. One article pointed to only one storm, Chantal, making landfall in the continental U.S. and low Accumulated Cyclone Energy. ACE is a jargony term that is meaningless to most of you reading this, but it grabs the attention of many colleagues in the weather community. A NOAA website defined ACE as, “A wind energy index, defined as the sum of the squares of the estimated 6-hourly maximum sustained wind speed (knots) for all named systems while they are at least tropical storm strength.”
At this point in the season, ACE is typically near 9, according to a blog post by meteorologist Brylee Brown, but it currently sits at just over 1 thanks to short-lived Tropical Storms Andrea, Barry and Chantal. As a reference point, Brown pointed out that ACE was close to 250 in the hyperactive 2005 season that produced Hurricane Katrina almost twenty years ago and exhausted the name list.
Candidly, this discussion gets to one of my pet peeves. Sure, ACE is low and only one storm has made landfall on U.S. soil, but those storms had significant impact. The remnants of Tropical Storm Barry were in the “moisture mix” that caused catastrophic flooding in Texas Hill Country, and Tropical Storm Chantal produced dangerous flooding in parts of North Carolina, including Durham and Chapel Hill. I continue to argue that there is too much of fixation with indices and scale categories rather than impact. Yes, they are useful for some aspects of risk communication but often overlook the full scope of impacts.
From a meteorological perspective, the Atlantic basin has experienced weeks of wind shear, plumes of Saharan dust, and unfavorable temperatures in the upper part of the atmosphere. Hurricane formation is impeded by such conditions, however, there are signs that conditions will become more favorable in the coming weeks. In fact, the latest European model ensemble “teases” something to watch in the coming week. I will come back to that in a moment.
I will respectfully push back on narratives that we are “off to a slow start.” The most active part of the Atlantic season is the period spanning August to October with September representing the climatological peak. As noted, by some metrics, this may be the “slowest” start since 2009. However, here is a reality check. The third named storm of the year typically forms on August 3. This year, the third named storm, Chantal, formed in early July. The first hurricane does not typically form until August 11, according to NOAA data. The first major hurricane (category 3 or higher) does not develop, on average, until September 1.
As we approach the first week of August, things are, well, doing what we expect them to do. Activity, particularly in the main development region of the Atlantic Ocean, starts to pick up. Hurricane expert Michael Lowry wrote in his Substack blog, “One feature most models are now picking up on is a fast-moving tropical wave set to emerge over the eastern Atlantic early next week.” He also indicated that some the newer AI models like Google’s DeepMindAI and the European AI ensembles are bullish on more activity around the week of August 3. The next named storm will be “Dexter.”
The peak of Atlantic hurricane season activity has not changed. What has changed is that in recent decades we have become more conditioned to expect activity before August 1. With such perspectives, it is understandable that an early 2025 season with 3 named storms by August is considered a “slow start.” Experts are still calling for average or slightly above-average season with around 8 hurricanes. We are entering the “find out” part of the year so prepare accordingly.
