x
Breaking News
More () »

Atlantic hurricane season forecast to be below average, here's why

If you haven't heard much about hurricanes or tropical storms in the Atlantic, it's not you. It's the weather.
Credit: maxuser

If you haven't heard much about hurricanes or tropical storms in the Atlantic, it's not you, it's the weather. That really isn't out of the ordinary, however, as the busiest period for tropical cyclones to develop is usually between August and late October.

Credit: maxuser

But even the busiest part of the Atlantic hurricane season may not be as busy as usual.

The National Hurricane Center updated their 2018 Atlantic hurricane forecast Thursday calling for below average tropical cyclone (hurricanes, tropical storms, depressions) activity. This is an update from their previous forecast in which the NHC called for average to above average tropical cyclone activity.

Credit: maxuser

It's not just the NHC, though. Another trusted forecast group, Colorado State University, also updated their forecast recently, calling for below average activity.

Credit: maxuser

So why? Why do forecasters believe this hurricane season won't be as busy as usual? Here are a few of the reasons.

1. Sea surface temperatures are cooler than average

The entire reason hurricanes - and storms in general - develop is to get rid of extra heat. A hurricane is like an engine whose job is to take that extra heat from the oceans and convert it into energy. That energy is manifested as a storm.

But look at the region outlined in red, labeled the Main Development Region (MDR).

Credit: maxuser

Those colors show the difference between average or normal temperatures and the current ocean temperatures. Blue indicates below average temperatures while yellow is above average. There is a lot of blue in the MDR, so there really isn't a lot of extra heat for storms to get rid of or even develop over.

2. Strong winds where storms develop

Living in the south where severe thunderstorms and tornadoes are part of the annual weather cycle, you may have heard the term "shear". Shear is a change in wind speed and direction with height. When it comes to severe storms in the warm seasons, shear helps storms live longer and makes them more dangerous.

But those storms and hurricanes have a different structure.

Credit: maxuser

Generally, shear is bad for hurricane development and sustainability. Hurricanes are most efficient when they are vertically stacked from top to bottom through the atmosphere. The shear inhibits the storm from being stacked and displaces the top of the storm from the bottom. When this happens, the rising motion of taking heat from the ocean and converting it into energy is hindered.

Shear will even destroy an already developed strong hurricane

3. Dry air from the Saharan Desert

Dry, dusty air from the Saharan Desert in Africa has made it all the way over the Atlantic Ocean to the United States this year, which isn't unusual but it gives you an idea of how far this dust can travel.

(Video: Ryan Maue, weathermodels.com, data from CopernicusEU)

Back to hurricanes. Caution, we are about to get even more science-y but you can understand it. Let's think of clouds as a liquid. Yes, clouds are made from evaporated water, which is a gas, but when that evaporated air is high in the sky it is condensed and considered a liquid.

The majority of energy in a hurricane comes from "latent heat release," similar to cloud formation. As the water changes state or phase from a gas (the muggy air we feel) to a liquid (clouds in the sky), the environment around the state change warms.

Credit: maxuser

When you introduce dry, Saharan air into the mix, that liquid (cloud) is then evaporated back to a gas which actually cools the surrounding environment. Hurricanes don't like cool air; they prefer it warm.

The dry air works as a double whammy with the shear to inject dry air into a moist environment not allowing storms to develop.

Overall, this is good news that the hurricane season in the Atlantic may be slower than usual. But, that low forecast doesn't mean a hurricane won't impact the U.S. mainland between now and Nov. 30 when hurricane season ends.

Before You Leave, Check This Out