Happy Monday and welcome to another edition of Beyond The Forecast!
Hurricane season is officially here, and it did not take long at all for us to have our first Tropical Disturbance in the Gulf of Mexico. Justin McKee recently wrote about how the season looks busier than an average year. Some of the key ingredients to a hurricane are low wind shear and high water temperatures; let’s look at how those factors influence how a hurricane forms.
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Atlantic hurricanes that affect the United States and the Caribbean start on the other side of the ocean off the coast of Africa. Initially, a few storms pop up without much organization. These storms start as individuals, but if there is a low-pressure center at the surface when the storms form, they can begin to rotate.
This rotation is on a broad scale, but it helps to combine the storms into a large, circular cloud pattern. The low pressure moves toward warmer water and allows it to rise. That rising, moist air eventually gets to a point where it cools and turns into even more clouds.
This consistent addition of moisture helps storms grow in both size and strength. That’s why the warm waters this year will help hurricane formation; there is more energy for a system to work with, which turns into higher wind speeds and more storm surge as the storm arrives onshore.
As a tropical cyclone moves over water, air at the surface is pulled into the center of the storm and forced to rise as it reaches that center.
The intensity of the rotating air at the center of the cyclone prevents clouds from forming, causing the clear “eye” of the storm.
Once the air reaches the top of the cyclone, it spreads out and turns into clouds farther away from the eye. These winds are necessary for hurricanes to form. Hurricanes form most easily when there is not much other wind to compete with.
If there are strong winds driven by other parts of the atmosphere, it can be hard for the hurricane to bring air in and gain energy. Low wind speeds this season will allow cyclones to develop without much interference.
A tropical system becomes a tropical storm when wind speeds top 39 mph and a hurricane when it passes the 74 mph threshold. The hurricane category system, the Saffir-Simpson Scale, is based on wind speed, but the storm surge of a hurricane is also very important.
The high winds drive water onshore and can cause even more damage depending on the particular hurricane.
Storm surge is largely a coastal issue, but high rainfall rates driven by a hurricane can cause localized flooding for more inland locations.
This week, there will be off-and-on storms with seasonable temperatures. Be sure to download our weather app for information on storms as they develop, and get Meteorologist Chris Michaels’ latest updates online.
You can always get specific forecast details for your zone, whether it’s the Roanoke Valley, Lynchburg area, the New River Valley or elsewhere around Southwest and Central Virginia, anytime at WSLS.com/weather. Know your zone!
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-- Marshall Downing