‘Homegrown' tropical storm could take shape along US Gulf coast
A tropical disturbance that is forecast to emerge in the northern Gulf of Mexico in the coming days has the potential to become the next named storm in the Atlantic basin and exacerbate ongoing flooding concerns in the Southeast, AccuWeather meteorologists say.
The formation of a homegrown tropical system from the northern Gulf of Mexico to waters along the southern Atlantic coast has been a concern for AccuWeather's long-range team of meteorologists over the past few weeks as fronts have stalled nearby, while moisture has surged into the Southeast, AccuWeather Meteorologist Brandon Buckingham said.
"This threat has risen as a result of a constant barrage of storms that have marched through the Plains and Ohio Valley, allowing cold fronts to drift unusually far south for this time of year and stall in the Southeast states," Buckingham explained.
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A homegrown tropical system is one that develops near the coast of the United States and is often the product of an area of low pressure that was previously over land. This setup does not happen every year, but it can be a potential starting point for tropical systems during the early part of the hurricane season.
The pattern helped to give birth to Tropical Storm Colin at the start of July along the South Carolina coast and has the potential to spin up the next tropical depression or storm of the year. The next named storm in the Atlantic will be called Danielle.
Prior to any official designation as a tropical depression or storm from the National Hurricane Center, AccuWeather is designating the system as a tropical rainstorm due to the potential for life-threatening and damaging flooding that could evolve this week.
The potential system's proximity to land may be a deterrent for development and is likely to prevent rapid intensification should a depression or storm take shape along the upper Gulf Coast. However, meteorologists say water temperatures are above average for this point in the season and are generally near 90 degrees Fahrenheit and well above the minimum threshold of 78 for tropical development.
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Wind shear is likely to remain rather low over the northern Gulf of Mexico as opposed to the waters along the southern Atlantic coast. Wind shear is associated with stiff breezes that blow from the same direction of change over different layers of the atmosphere. When wind shear is strong, it can limit or prevent tropical activity in most situations. Wind shear is forecast to remain high over much of the rest of the Atlantic basin for the remainder of the week.
A tropical depression or storm would not be able to churn seas to the point of being a major threat to petroleum operations in the Gulf. However, even a tropical storm can generate dangerous rough surf, beach erosion and gusty winds for coastal interests. Downpours and the threat of lightning strikes can also disrupt daily activities.
The tropical system could form anywhere from the Louisiana coast to the northern Florida Gulf coast and waters just offshore later this week.
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Thunderstorms associated with a stalled front will continue to drench the Southeast states this week, according to AccuWeather Meteorologist Mary Gilbert. "The heaviest of these downpours will begin to hone in on a more confined portion of the Gulf Coast as the potential tropical concern arises," Gilbert said.
Rainfall will ramp up as the circulation from the budding tropical system begins to pump more moisture northward from the Gulf of Mexico. A general 4-8 inches of rain will fall along the central Gulf Coast region, from southeast Louisiana to the Florida Panhandle, even if the tropical system fails to form due to its slow-moving nature. An AccuWeather Local StormMax™ of 15 inches could fall if a tropical storm were to develop.
Cities such as Biloxi, Mississippi; Mobile, Alabama; and Pensacola, Florida; should be prepared for downpours capable of causing flash flooding. New Orleans, which sits several feet below sea level, is especially prone to flooding during prolonged heavy rain situations where stormwater pumping operations can be overwhelmed.
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"In August 2016, an unnamed tropical system unloaded a tremendous amount of rain and triggered life-threatening flooding on roughly the same area of concern as this week," AccuWeather Hurricane Expert Dan Kottlowski said. The slow-moving system unloaded up to 31 inches of rain in southern Louisiana over a seven to 10-day period and was associated with dozens of fatalities and damage of $10-15 billion.
AccuWeather meteorologists say travel along a portion of Interstate 10 could be adversely affected at times due to the persistent rainfall and downpours produced during the pattern which could far exceed the amount of rain needed to alleviate current drought problems.
"The threat of flash flooding from persistent thunderstorm activity is likely to rise from the Florida Panhandle to southern Louisiana this week," Buckingham said. Downpours from a tropical system will be in addition to the showers and thunderstorms produced by the stalled front and moisture in the region.
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Farther west, a slight flow from the north may limit or prevent most downpours from expanding across Texas. If the tropical system were to form and wander farther to the west or remain weak and sprawled out, then more moisture could be pumped into the Lone Star State. Sporadic downpours in Texas are most likely along the upper coast.
Forecasters say that it's possible for a tropical depression or storm to form right on the coast or even over land in this current setup.
Tropical storm formation over land is rare, but the land along part of the upper Gulf Coast is swampy and strewn with bayous and large estuaries that can occasionally support this occurrence. In 2021, It was believed that Tropical Storm Claudette formed over land in southern Louisiana. Later analysis by the National Hurricane Center determined that the storm formed just prior to moving over land.
In 2016, Julia strengthened from a tropical depression to a tropical storm after moving over land in northeastern Florida.
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