A broad area of low pressure is forecast to bring heavy rain and flooding along the Texas coast over the next 48 hours, with the potential for the system to build and move inland, the National Hurricane Center (NHC) has said.
The system is currently located just off the Texas coast and is producing showers over the adjacent waters of the Gulf of Mexico.
While the chance of a cyclone forming in the short to midterm remains low, residents are being warned to expect heavy rains and flash flooding over the coming days.
"A broad area of low pressure just offshore of the upper Texas coast continues to produce some disorganized shower activity near the coast and over the adjacent waters of the northwestern Gulf of Mexico," the NHC said in a Tropical Weather Outlook on Monday.
"This system is expected to meander near the coast for the next couple of days, and some slow development is possible if it remains offshore," it said. "By Tuesday, the system is forecast to move inland, and further development is not expected.
"Regardless, heavy rains could cause some flash flooding across portions of the Texas coast during the next couple of days."
While the likelihood of a cyclone developing remains low—the NHC says the chance is just 10 percent over the next seven days—people in affected portions of coastal Louisiana and upper Texas are being told to expect flash flooding.
According to the National Weather Service (NWS), flash floods usually occur within three to six hours of heavy rainfall.
Several factors affect the likelihood of flash flooding, including the intensity and location of rainfall, the land use and topography of an area, vegetation types and growth density, soil type, and soil water content.
Areas with particularly dry soils or those that have been previously scorched by wildfires—known as burn scars—allow for run off that can contribute to such flooding events.
Urban areas are also vulnerable to flash flooding.
"Rainfall (from the same storm) over an urban area will cause flooding faster and more-severe than in the suburbs or countryside," the NWS said. "The impervious surfaces in the urban areas do not allow water to infiltrate the ground, and the water runs off to the low spots very quickly."
Meanwhile, the NHC is keeping a close eye on two other systems brewing in the Atlantic, both of which have a 40 percent chance of developing into a cyclone over the next week.
The first, currently located over the Lesser Antilles and Caribbean Sea, "is expected to move westward and cross the eastern Caribbean Sea through Tuesday with little development," the NHC said.
However, "environmental conditions are forecast to become more conducive for development while the system moves across the central and western Caribbean Sea during the middle and latter parts of the week, and a tropical depression could form during that time."
The second system is located further east along the coast of Africa and is producing a large area of showers and thunderstorms.
"A tropical depression could form in a few days while the disturbance moves slowly west-northwestward or northwestward over the eastern tropical Atlantic Ocean," the NHC said.
A tropical cyclone originates as a tropical depression, marked by groups of thunderstorms surrounding a low-pressure center but lacking the organized structure of more powerful systems.
When wind speeds exceed 39 mph, the system is classified as a tropical storm. If winds intensify to 74 mph, it becomes either a hurricane or, in the Northwest Pacific, a typhoon.
For these cloud clusters to develop into a tropical cyclone, specific conditions must be met: warm, moist air from tropical oceans with sea surface temperatures of at least 27 degrees Celsius; converging surface winds that lift air to create storm clouds; low wind shear, which allows the storm clouds to rise vertically; and sufficient distance from the equator to provide the necessary rotational spin.
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