It’s been since flash-in-the-pan Colin on July 2nd that a tropical cyclone has formed anywhere in the Atlantic.
Since Colin – which unraveled only 24 hours after it formed over the Carolinas – nearly two weeks have passed, and even would-be storms, like the northern Gulf disturbance that moved inland yesterday, haven’t mustered up anything more than a low odds of development.
With tropical development not expected through the weekend, you might start to wonder how usual it is to go this long without an Atlantic storm in the middle of summer.
As it turns out, it’s more typical than not.
In the modern record, the formation of tropical depressions, storms or hurricanes in July are spaced out on average about every two weeks.
The same holds for June.
By August, as hurricane season ramps up, the conga line of storms increases, with storms forming on average every 10 days, and by September, tropical cyclone formations occur every five days or so on average.
So a two or three week lull in September, unlike in July, would be more unusual.
It’s certainly happened – 23 days elapsed between Josephine and Kyle in September 2008 and 21 days between Hortense and Isidore in 1996 – but by September, the Atlantic is usually hitting its seasonal stride.
Hurricanes are a lot like bananas – they tend to come in bunches.
Whether it’s here in the Atlantic or over in the Pacific, formations often clump together. To use a more cliché euphemism, when it rains in the tropics, it pours.
The biggest factor regulating these fits and starts is an oversized configuration of winds high up in the atmosphere known as the Madden-Julian Oscillation or MJO, which straddles the equator and moves eastward across the globe about every month or two.
The MJO is like an big tropical see-saw, with its rising side favoring storminess and tropical activity, and its sinking side reducing storminess and tropical activity.
Not surprisingly, the Atlantic has been feeling the influence of the less conducive sinking branch of the MJO in recent weeks.
While isolated tropical systems can form when the MJO is in a less conducive state, especially outside of the deep tropics, things tend to look like they have this week, with only wispy cloud cover and anemic storminess.
The less active pattern should hold on for much of July across the Atlantic, so expect the welcome lull to lead us into August.
The eastern Pacific, on the other hand, is having no trouble cranking out storms.
The Pacific typically flips on its switch in July versus the Atlantic which comes in late August and September, so the activity is right on cue.
Darby, which became the strongest hurricane so far in 2022, continues to defy forecasters, briefly re-strengthening yesterday over open Pacific waters despite forecasts to the contrary.
Another storm is expected to form by this weekend in the eastern Pacific, but like Darby, poses no threat to land.