Bertha Is a Lopsided Tropical Storm. Here's Why That's Important

Tropical Storm Bertha is moving along the Gulf Coast of the United States, bringing rain, wind, and the chance of flooding. People living near the coast need to stay alert, but scientists say the storm is not likely to grow into a major hurricane. Special winds high in the sky are helping to keep Bertha from getting stronger.

If you look at satellite images of Bertha, it looks lopsided — heavier on one side than the other. That uneven shape is actually a good sign for people in hurricane-prone areas. It means the storm is being disrupted by something called wind shear, which is when winds at different heights blow in different directions and tear a storm apart.

On the afternoon of July 21, Jamie Rhome, the deputy director of the National Hurricane Center, said Bertha was probably as strong as it was going to get. The National Weather Service office in New Orleans said wind shear was expected to increase through the night and into July 22. Those stronger winds should cause Bertha to weaken and keep the heaviest rain far to the south and southwest of New Orleans.

Still, weather forecasting is never totally certain. Bertha actually picked up some stronger winds on the morning of July 21, and its path shifted slightly to the north overnight. While forecasters say chances are getting smaller, there is still a risk that Bertha could bring worse impacts if it changes course or gets stronger.

Here is what forecasters expected as of July 21. Minor to moderate coastal flooding was possible between the Mississippi-Alabama border and the mouth of the Mississippi River, with water levels rising up to 4 feet in some spots. Flash flooding could happen through July 24 along the Gulf Coast, and peak wind speeds were forecast at 45 mph near the coast on July 23.

Andy Hazelton, a scientist at the University of Miami, said the conditions around Bertha are common for July. Because the shear is coming from the north, most of the heavy rain — called the "dirty side" of the storm — is staying out over the open water. Hazelton said Bertha looks a lot like Hurricane Barry, a poorly formed storm that hit in July 2019.

Like Barry, Bertha is also forming during the beginning of an El Niño period. El Niño is a weather pattern that warms parts of the Pacific Ocean and is known for creating wind shear that stops hurricanes from forming in the Atlantic. Brian McNoldy, another hurricane scientist at the University of Miami, described Bertha as "a marginal storm in marginal conditions."

The name Bertha has been used for Atlantic storms for many decades. Most storms with that name have not been very powerful, but scientists remind us that even weak tropical storms can be deadly. Nine people died because of Tropical Storm Bertha in 1990, and two people died from rip currents caused by Hurricane Bertha in 2014. These examples show that no tropical storm should ever be taken lightly.