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Up to 2 feet of rain to deluge Gulf states as storm brews offshore

By
Alex Sosnowski, AccuWeather.com
This image from early Wednesday shows thunderstorms gathering over the northern Gulf of Mexico. Image courtesy of  NOAA
This image from early Wednesday shows thunderstorms gathering over the northern Gulf of Mexico. Image courtesy of  NOAA

July 10 (UPI) -- Residents along the Gulf Coast should begin bracing for heavy rainfall and a possible damaging storm surge as the formation of a tropical storm -- the second named system of the Atlantic hurricane season -- is increasingly looking like a certainty late this week. Tropical Storm Barry has a near 100 percent chance of forming, AccuWeather forecasters say, and, depending on the track it takes, the storm could flirt with becoming a hurricane before making landfall.

"AccuWeather meteorologists believe this system will become a tropical depression on or before Thursday and Tropical Storm Barry by Friday," according to AccuWeather Hurricane Expert Dan Kottlowski.

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"We expect the budding tropical system to drift southwestward over the northern Gulf of Mexico into Wednesday night then take a more westerly track on Thursday," Kottlowski said.

This track takes the feature far enough away from the coast to allow for significant strengthening. Wind shear is low over this portion of the Gulf of Mexico.

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"Barry could become a hurricane, depending on how long the system remains over the warm water," Kottlowski said.

Water temperatures in the northern Gulf of Mexico are in the middle to upper 80s F.

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"Right now, our greatest concern is for torrential rain that would result in life-threatening flooding," Kottlowski said.

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The system has begun to produce torrential rain in southern Louisiana. Several inches of rain have poured down on and has resulted in street flooding New Orleans during Wednesday morning.

Given the westward, slow-moving nature of the storm, a general 2 to 8 inches of rain is likely from the Florida Panhandle to the upper part of the Texas coast.

However, near and just north of where the center of the storm makes landfall, rainfall is likely to increase at an exponential rate.

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"The heaviest rain is expected to fall on parts of Louisiana, Mississippi, western Tennessee, Arkansas and northeastern Texas," Kottlowski said.

AccuWeather is forecasting up to 24 inches from this developing tropical system.

Southeastern Texas may also receive similar rainfall, but only if the storm were to move ashore along the western Gulf coast.

Enough rain may fall to produce everything from street and highway flooding to small stream, bayou and river flooding.

A track of the storm center into south-central Louisiana may bring relatively little rain to much of southeastern Texas.

However, a track into the middle part of the Texas could could produce tremendous rainfall in the Houston and Port Arthur area.



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"A second concern we have is for storm surge flooding," Kottlowski said.

Even a relatively weak, slow-moving tropical storm, on its eastern side, can pump a significant amount of water northward from the Gulf of Mexico.

Officials in New Orleans are monitoring for any potential storm surge impacts on the Mississippi River.

"The city is protected to a project height of 20 feet. There is still a great deal of uncertainty regarding potential impacts, so please continue to monitor the forecast over the next several days for the latest information," the National Weather Service in New Orleans said in a tweet.

The stronger the system becomes before landfall, the greater the risk of a significant storm surge near and north and east of the center of the storm.

People in coastal areas should be prepared to protect property from minor to moderate coastal flooding later this week and this weekend.

"Another concern is for wind associated with the storm," Kottlowski said.

How strong the feature becomes will determine the strength of the wind. However, there is potential for the system to become a hurricane should it remain offshore into Saturday.

Even in lieu of a hurricane, sometimes tropical storms that are near the coast or make landfall can unleash sudden tornadoes. Some of the tornadoes can be wrapped in rain and difficult to see until the storm is already upon a neighborhood.

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A tropical depression, tropical storm or minimal hurricane is likely to have little to no impact on operations of offshore oil and gas rigs.

A major hurricane in these areas could significantly impact production. Most offshore oil and gas rigs in the Gulf of Mexico are in the north-central and western portion of the basin.

Four of the largest oil refineries in the world, based on processing capacity, are located in Louisiana and Texas.

Even in absence of a hurricane, gusty thunderstorms and isolated tornadoes associated with a tropical depression or storm can be a threat to lives and property.

Regardless of the strength of the storm prior to landfall, rip currents, seas and surf will build throughout the Gulf of Mexico for the remainder of this week and into the weekend.

Squalls will intensify in the eastern Gulf and begin to propagate westward with the movement of the storm.

Waterspouts can be spawned in some of the squalls over the Gulf.

Development of tropical storms in near-shore waters off the U.S. coast are common early during hurricane season, in the middle of the summer.

Tropical storms can form from old cool fronts that stall over the Deep South or along the Atlantic coast.

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Another way tropical storms can form is like the situation this week.

A storm in the middle layer of the atmosphere can form or drift over the Gulf of Mexico or the Atlantic.

While this type of storm is not tropical in origin, it can slowly spin down to the surface and initiate a tropical or sub-tropical storm.

Formation of tropical storms near the United States is different than the more commonly known tropical storms that originate from the west coast of Africa from late summer to the early autumn. This part of the tropical season is known as the Cabo Verde season. The Cabo Verde islands are located just off the coast of Africa.

While hurricanes can form in near-coast areas of the United States, often the most powerful hurricanes are spawned in the Cabo Verde manner and can travel thousands of miles to the west and reach the Caribbean and North America.

Kottlowski has been warning since early April that the Gulf of Mexico, as well as areas east of Bermuda and off the southeastern coast of the United States, need to be watched closely for early season development due to water temperatures running above normal.

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While El NiƱo conditions may suppress the number of tropical storms and hurricanes in the Atlantic basin somewhat this year, all it takes is for one or two hurricanes to strike populated areas and result in great risk to lives and property.

Tropical Storm Emily from 2017 was the last time that a named tropical system made landfall in the United States during the month of July, which is typically a quieter month in the Atlantic ahead of peak hurricane season that spans from mid-August to mid-October. Emily formed in the eastern Gulf of Mexico and moved into the central Florida Peninsula on the last day of July.

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