(WFXR) – Summer weather means spending time outside, having fun, and being active.
It’s also the time of year that coastal interests need to pay close attention to developing tropical systems.
One key element that’s needed to develop a tropical system is spin. At the start of the season — in June and July — we mostly look close to home for the development of a tropical system. In the later summer months, we look more out to sea such as the west coast of Africa for systems to emerge into the Atlantic.
One main component we look into is some organized convection to come off the coast of Africa. Depending on the organization of that system, it can develop into a tropical depression — which is a semi-organized area of low pressure with a closed circulation that has winds less than 38 mph.
As it develops, the next phase of the system’s organization is a tropical storm — which is a stronger system than a tropical depression and has winds between 39-73 mph. At this point, the National Hurricane Center (NHC) in Florida will then give the system a name.
As it moves over the Atlantic, the system can strengthen even further and officially develop into a hurricane. Hurricanes are classified into a category system. A low-end hurricane is considered a Category 1 with winds between 74-95 mph. These storms can start to churn up the waves as becomes more organized.
If the system further strengthens it can develop into a Category 2 hurricane with winds between 96-110 mph. These storms can bring significant coastal flooding.
Next up is a Category 3 hurricane with maximum winds between 111-129 mph. When storms reach this level of strength, they are deemed a “major hurricane.” This is the same strength that Hurricane Katrina was when it made landfall near the mouth of the Mississippi River back in 2005.
Hurricanes can still grow in intensity. If a system has winds of between 130-156 mph it is labeled a Category 4. These systems can bring widespread catastrophic damage, especially right along the coastline and inland we’re talking major impacts from flooding, wind, and tornadoes.
Finally, at top strength, is a Category 5 hurricane. These storms have maximum winds of at least 157 mph, and while very rare, we have seen an influx of tropical systems get to this magnitude in recent years. magnitude.
While only four hurricanes have ever made landfall at this strength there have been other Category 5 systems.
Most recently, Lorenzo and Dorian back in 2019; Maria back in 2017 (which devastated Puerto Rico); and Irma also in 2017. While Irma did make landfall in the Gulf of Mexico, its strength had downgraded and it wasn’t at Category 5 strength.
There are a lot of factors that need to be in place before these systems can develop.
One of them is a lack of wind shear which is the changing of wind speed and direction with height. Weak tropical systems that interact with wind shear can be significantly affected, especially if that shear is strong.
Below is an image describing how wind shear interferes with the tropical system’s development. As strong upper level winds interact with a weak tropical system, it can make it lopsided.
Looking at the system from the top, as upper level winds come in, it can make the system less circular which can throw the system’s equilibrium off and forces it to weaken, and potentially it will dissipate.
However, with a stronger system, the shear can have similar impacts but be less severe to the system’s organization.
The shear can still tilt the system inhibiting development, but since the storm is stronger it takes more effort for the system to rapidly weaken. In a stronger storm, such as a hurricane coming in contact with upper level wind shear, the weakening process is generally slower and takes longer to significantly weaken it.
Another key element that we watch for is ocean temperatures. In the sample map below, we’ve placed a wide range of temperatures showing where strengthening of a tropical system is more likely.
Typically, systems need ocean water of 80 degrees or greater in order to strengthen, which is why areas in the Gulf of Mexico and the Caribbean are prime locations for development.
Systems can still strengthen with ocean temperatures into the upper 70s, but other conditions need to be in place, such as no vertical wind shear. Once sea surface temperatures get below the mid-70s, there isn’t enough energy for tropical systems to draw from unlike in the warmer temperatures which can enhance the development.
It could be a very busy season in the Atlantic basin. So be aware of what’s out there in the open waters and, of course, be sure to watch the WFXR Pinpoint Weather Team all hurricane season long for the latest updates on the tropics.