It’s no secret that the 2018 hurricane season hasn’t been all that active thus far. With 3 named storms, one of which was sub-tropical, no impact on the United States coastline, and nothing but dying tropical storm Debby in the northern Atlantic, one has to wonder what the rest of the hurricane season will bring. Hopefully we can provide some answers for you.
The average peak of hurricane season is exactly a month from this week (typically the middle of September is when we see the most activity), so there’s certainly time for things to pickup. However, for the time being we aren’t seeing very strong signs of an increase in activity. That being said, as we look ahead in time towards the longer range, we do believe that we’ll begin to see an uptick across at least part of the Atlantic Basin. Let’s take a look at the basics.
Tropical activity accelerates when three main things are in place: warm surface ocean temperatures, low wind shear, and convection. Taking a look at the Atlantic Basin, it’s clear that overall temperatures are fairly below-average, with the only exceptions being the Caribbean Basin and the northern Atlantic. The key areas for development this time of year, however, typically reside across the southern Atlantic Basin off the coast of Africa, where temperatures are generally either average or slightly above-average. That’s where our other factors come into play.
The next thing we like to investigate with hurricane development is wind shear and inhibitors such as the Saharan Dust layer off the coast of Africa. The area where we typically see strong development this type of year across the southern Basin has above-average wind shear, but nothing extreme. Storms should still be able to form. The real issue is the intense SAL (Saharan Air Layer) coming off of Africa.
Atlantic Basin Wind Shear:
Notice in the image above from the ECMWF displaying Deep Layer Wind Shear, the most consistent and strongest wind shear residing over the Caribbean basin. There are more breaks in the wind shear action further to the east.
The above image was captured during the end of July from the GOES-16, and clearly shows the massive amount of Saharan Dust as seen from space. This is a death sentence for all tropical activity trying to form underneath. So while ocean temperatures remain average to slightly above-average and there are breaks in the deep layer wind shear, nothing is forming with that level of SAL.
This SAL is actually so extensive that it has even inhibited development further to the west, closer to the United States. This is quite unusual. We can probably attribute it to the lack of rainfall and extreme heat across much of the African continent. We may even see this increase in the coming years as overall global temperatures continue to rise.
Now switching gears, let’s take a peek at what the rest of the season holds and whether we’ll see an increase in tropical activity.
The SAL is most likely here to stay, ocean temperatures are unlikely to waver very much, and shear will be quite volatile. Warmer temperatures closer to the US coastline with increasingly favorable conditions is really the only hotspot to watch. We often refer to systems that grow out of this environment as “homegrown tropical storm systems.”
Towards the end of this month and especially in September and early October, these are the areas we will be watching most closely for development. The biggest issue we’ll have to keep an eye on is if/when we do get some development, do we end up seeing rapid intensification under very warm waters prior to coastal impact?
You can already see that the Tropical Cyclone Heat Potential is displaying something fairly similar to the areas we’re watching during the second half of the season for development. What you’re seeing in the Caribbean basin is the potential for more rapid, explosive development, so once shear relaxes in that area, it could become a hot spot.
While the National Hurricane Center (NHC) has lowered original estimates on the season, they’re still in line with the thinking that several more hurricanes and perhaps a major hurricane or two is within the cards for the rest of the season. For that to happen, this is the region where it’s most likely to take place. We’ll be keeping a close eye on this over the next several weeks and months.