By AccuWeather senior meteorologist
Updated Jun. 16, 2021 4:49 PM PDT
AccuWeather meteorologists are predicting that the third tropical system of the 2021 Atlantic hurricane will take shape in the Gulf of Mexico this week with its eyes set for a portion of the United States. Forecasters expect the system to aim for the central Gulf Coast, where it will unleash torrential rainfall and flooding late this week into the weekend.
The chance for tropical development has steadily risen over the past week, and a system is projected to develop sometime from late Wednesday night into early Saturday over the western Gulf of Mexico. The next name on the list of tropical storms for this year in the Atlantic basin is Claudette.
"As this system slowly brews, it is forecast to take a general northward path toward the U.S. central Gulf Coast this weekend," AccuWeather Senior Meteorologist Rob Miller said.
As of Wednesday, this disturbed area remained poorly organized, but that is expected to change soon.
"Some tropical development of this disturbance is likely, even though wind shear, dry air and land interaction will be inhibiting factors," Miller said.
Strong wind shear occurs when winds rapidly change in direction or speed across an area, or at different levels of altitude, and can limit development of tropical systems or cause some tropical systems to weaken.
However, despite the environmental hurdles that the system will have to overcome in order to develop, one factor that favors formation of a tropical system remains steady. Waters over much of the Gulf of Mexico are in the 80s F, which AccuWeather forecasters say are plenty warm enough to nurture a tropical system.
"Even though a high-end tropical system, such as a hurricane, is unlikely in this case, a mere tropical depression or tropical storm can unleash a tremendous amount of rain once over land, and that remains the primary concern at this time," Miller said.
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Exactly where the system forms in the first place will determine where landfall is most likely.
"Landfall may occur anywhere from near the Texas-Louisiana border to perhaps the western part of the Florida Panhandle," Miller said. At this point, AccuWeather meteorologists have pinpointed late Friday to Saturday as the most likely time frame, and the Louisiana coastline is the most likely place for landfall.
Forecasters are urging people to not just focus on the forecast point of landfall, as impacts from tropical storms are often very spread out.
"Since southwesterly wind shear is already affecting the feature and is forecast to continue to do so through landfall, much of and perhaps all of the downpours will occur on the eastern side of the storm center and may extend across hundreds of miles," Miller said.
Given the general northward projected movement of the storm, much of Texas should be spared from the system's rainfall, even if landfall were to occur as far west as the upper Texas coast. The system would have to buck steering winds and shear to roll ashore along the southern Texas coast. This is the only scenario where heavy rain might be thrown over much of southeastern Texas.
The southwesterly winds occurring at mid- and upper levels of the atmosphere above the system will tend to push showers and thunderstorms along well ahead of the center. As a result, downpours directly associated with the system can begin as early as Friday along a portion of the central Gulf Coast.
Weather conditions are expected to deteriorate from the upper Texas coast through the Florida Panhandle Friday with the potential for tropical storm conditions for a time this weekend.
A tropical storm has maximum sustained winds of 39 to 73 mph with higher gusts.
"Even a weak to moderate tropical storm or tropical depression will cause rough and dangerous seas and surf with strong rip currents as well as rising coastal waters, overwash and minor coastal flooding along the upper Gulf Coast," AccuWeather Senior Meteorologist Paul Walker said.
Some low-lying coastal roads and shoreline communities could be inundated.
As AccuWeather meteorologists have been predicting since early June, there is the likelihood of low-lying area, street and highway flooding due to heavy rain and the risk of small stream, bayou and major river flooding due to the system's persistent downpours over a portion of the Southern states.
"The storm, regardless of strength, has the potential to deliver rainfall rates of 1-2 inches per hour over a several-hour period," Miller said.
That amount is more than enough precipitation to overwhelm storm drains and perhaps even pumping systems in New Orleans, which sits several feet below sea level.
Given the current outlook of the track of this system, the heaviest rainfall may potentially fall in southern and eastern Louisiana, southern Mississippi, southwestern Alabama and the western part of the Florida Panhandle. This zone has the highest potential to pick up 8-12 inches of rain over a 24- to 48-hour period with an AccuWeather Local StormMax™ of 20 inches in 72 hours.
However, a broad area of 2-8 inches of rain is possible from near the Texas and Louisiana border to the eastern part of the Florida Panhandle and perhaps as far to the north as the southern border of Tennessee.
Much of the area from southeastern Texas to Mississippi has measured 1-2 feet of rain since early May, which is three to four times the average rainfall for the region. To say the least, the ground remains saturated and water levels are already high.
After heavy rain fell just last week over part of the South Central states, some rivers from northeastern Texas to northern Mississippi and western Alabama experienced a surge of water that was producing minor, moderate to major flooding, according to the National Weather Service. Portions of rivers that were experiencing flooding in the South Central states as of Wednesday included the Sabine, Quachita, Big Sunflower, Big Black, Yazoo, Pearl and Tombigbee.
There are two different possibilities of how the system will behave after landfall. One possibility is that heavy rainfall may continue to expand northeastward over the Southeastern states through early next week as the system maintains some organization. By maintaining minimal strength, it would continue to pull Gulf of Mexico moisture in and cause heavy rain to expand northward and eastward across the interior South. In this case, the center of the storm might potentially reach the Carolina coast and reorganize over the Gulf Stream over the western Atlantic.
Another scenario is that the storm will weaken rapidly after moving inland. In this case, torrential rain and flooding problems may be limited to areas south of Interstate 20 in Louisiana and Mississippi with only spotty downpours farther to the north and east.
Should the system become a tropical storm, it would become the third named storm of the season in the Atlantic basin.
And even though the 2021, Atlantic hurricane season is still young, development of the third storm in this time frame would be far from a record. That earliest third named storm on record is held by Cristobal from last year. Cristobal formed on June 2, and beat the prior record-holder Tropical Storm Colin from 2016 by several days. Colin formed on June 5. Tropical Storm Cristobal made landfall along the central Gulf Coast of the U.S. after forming in the Gulf of Mexico from the remnants of eastern Pacific Tropical Storm Ana, which moved inland over Central America before crossing over.
Beyond the emerging threats in the Gulf of Mexico, AccuWeather meteorologists anticipate a very active hurricane season for 2021 with 16-20 named storms and three to five direct impacts on the U.S.
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