Flooding downpours from Gulf tropical rainstorm expanding inland

As a tropical rainstorm swings from the Gulf to the lower Mississippi Valley through the end of this week, tremendous downpours can trigger flash flooding in urban areas as well as quick rises on some bayous and rivers.

A tropical rainstorm has run out of time to strengthen into a depression, but downpours from the slow-moving storm will unleash torrential downpours that can lead to dangerous and disruptive flooding, AccuWeather meteorologists warn.

The focus of the storm's heaviest rainfall will extend across a large part of Louisiana, including some major cities along Interstate 10 from Lafayette to Baton Rouge, Lake Charles and New Orleans.

Early Thursday morning, the poorly defined center was just east of New Orleans, with most of the thunderstorms over the Gulf or right along the coast of Louisiana and Mississippi.

However, an eruption of drenching thunderstorms is foreseen over the South Central states from Louisiana to portions of Mississippi and far northeast Texas as the storm moves inland and moisture is flung onshore from the Gulf. Because of this, Gulfport, Mississippi, Mobile, Alabama, and Pensacola, Florida, may experience episodes of flooding downpours.

Even a poorly organized tropical rainstorm can still produce localized torrential downpours that can lead to incidents of dangerous flash flooding.

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Weighing the "what ifs" and what is most likely, the AccuWeather RealImpact™ Scale for Hurricanes is a one, due to the potential for travel disruptions, loss of revenue and the risks to lives and property in the United States associated with heavy rainfall and flooding.

Weak steering breezes will guide the rainstorm westward over southern Louisiana on Thursday. At that point, steering breezes may drop off, which could allow the rainstorm to stall and continue downpours over the same area.

The downpours will expand to near the Texas border and northward to the Arkansas border into the end of the week.

A sizable zone where 4-8 inches of rain is forecast to fall extends across much of the southern half of Louisiana and part of southern Mississippi. Within this zone, pockets where 8-12 inches of rain can fall are anticipated with an AccuWeather Local StormMax™ rainfall of 16 inches.

Rainfall rates of 1-3 inches per hour can occur during the storm, which is enough to challenge the storm drainage capabilities in some of the metro areas in southern Louisiana, including New Orleans. New Orleans sits below sea level and relies on powerful pumps to keep streets and neighborhoods free of standing water.

Some flooding in low-lying areas is anticipated along with flash flooding in urban locations over portions of Louisiana, southwestern Mississippi and areas in Texas near the Louisiana border.

From Friday to the weekend, drenching downpours are likely to expand over the lower and middle portions of the Mississippi Valley with pockets of flash flooding.

Because of the minimal gain in strength anticipated by the tropical rainstorm, strong wind gusts will generally be limited to thunderstorm activity near the Interstate 10 corridor.

"It is possible that a couple of tornadoes and waterspouts develop near the central Gulf coast as the storm moves inland on Thursday," DaSilva said.

AccuWeather meteorologists are watching the nearby waters of the United States for tropical development later this month.

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