Last year, they were already on the letter I (nine storms) by August. This year, we’re only on F (six storms). Is there a specific atmospherical reason for this, or is it just a strange coincidence?
Edit – I’m mostly talking about the US and that area, but if you’ve noticed the same thing in your geographical area, feel free to share.
In: 176
Geologist here so I may be able to provide some insight (caveat: I only took meteorology in undergrad and have not applied it in my career).
Simplifying it because ELI5:
For tropical storms to form you need a combination of three things. Warm ocean water temperatures, more uniform wind speeds in the air aloft, and air moisture content.
So let’s look at what’s happened so far this year:
As I understand, ocean water temperatures have been above 80F, which is the minimum temperature needed. So, we can rule that out.
Wind shear has been higher this year than usual, which has been detrimental to cyclone formation.
Dry air from the Sahara has been funneled over the Atlantic Ocean due to prevailing weather conditions in the area.
All these factors have resulted in a weaker than usual season.
That being said, weather patterns are changing. The warm water conditions will continue, and weather forecasts have been calling for weaker trade winds. There is also the arrival of the west African monsoon season. All these factors may result in a fairly active hurricane season – remember, the hurricane season goes to November.
Edit to add: I assumed OP was referring to the Atlantic hurricane season. As I understand, the Pacific hurricane season has been fairly average so far.
Edit continued: to clarify, *hurricanes* are used as a terminology in the Atlantic and northeastern Pacific oceans. *Typhoons* are used to refer to the same storm in the northwestern Pacific and *cyclones* are used as a term in the southern Pacific and Indian oceans.
We don’t know
It was expected to be an above average year because of La Nina in the Pacific bringing warmer weather that feeds the storms
La Nina has stuck around as expected but we’re quite a bit below average for storms with the total energy being about half of average and the count being 5 vs 8 storms when we hit peak on 9/10 before Fiona, I don’t have numbers on how the energy has changed with her in the mix
There has been strong upper level winds in the tropics which hurts storm formation but its a significant drop off from prior years.
This is another case of climate being more predictable than weather. Our forecasting has gotten way better over the last few decades but sometimes a new variable comes into play that just didn’t matter in prior years so this year will likely result in better models for the future
Because the instability from climate change doesn’t only result in an increase of weather events, like it did last year and the year before, it causes a wider variation in the number of weather events. This can lead to fewer than normal storms as well as greater than normal storms. There isn’t any specific reason (or rather, there are any number of specific explanations) for “why” there is either an increase or a drop; weather is chaotic and not easily predictable. But both more and fewer than normal numbers of storms becomes more likely because of anthropogenic global warming.
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