US Gulf Coast put on alert for potential tropical storm to form late week

By Kristina Pydynowski, AccuWeather senior meteorologist

After more than a month of inactivity in the tropical Atlantic basin, development is likely in the northern Gulf of Mexico with potential impacts to residents and visitors later this week and this weekend.

A non-tropical system tracking through and triggering showers and thunderstorms across the South early this week will eventually end up over the warm waters of the Gulf of Mexico around midweek.

"The storm will then sit over the Gulf of Mexico for a few days and may eventually become partially or fully tropical in nature during the time period from late this week into next weekend," according to AccuWeather Senior Meteorologist Adam Douty.

Dry air, dust and strong wind shear has prevented tropical development across the Atlantic basin since Subtropical Storm Andrea briefly roamed the waters of the west-central Atlantic in late May.

However, more conducive conditions exist over the eastern Gulf of Mexico.

With strong wind shear absent, warmer-than-normal waters of the eastern Gulf of Mexico can allow an organized tropical or subtropical system to take shape.

The next tropical storm in the Atlantic basin would be called Barry.

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A subtropical storm has both tropical and non-tropical characteristics, but can have must as much impact in terms of heavy rain, rough seas and strong winds.

"One of the keys to whether a depression or storm will form is how close the system tracks to the coast," Douty added. "The longer the system remains over water, the stronger it may become," he said. "However, it may stay non-tropical if it stays near land."

Development of the feature will be slow initially. However, once it catches, and if the feature remains offshore, it could gain strength at a fast pace.

"Since there is a chance for the feature to move over open water, it is premature to say that the only threat will be from torrential rain," according to AccuWeather Senior Meteorologist Alex Sosnowski.

The latest trends in steering winds suggest more of drift toward the central and western Gulf of Mexico this weekend.

"There are a number of petroleum rigs and refineries along the central and western Gulf coast, and there may be considerable risk if this storm ramps up, develops to its full potential and travels in that direction," Sosnowski said.

Seas would turn dangerously rough for boaters and swimmers as the storm strengthens.

Regardless of development, the system may lead to multiple days of showers and thunderstorms that can spoil vacation and outdoor plans across the Southeast this week.

Flood dangers can arise in areas that get hit repeatedly by downpours or where a more concentrated band of heavy rain unfolds.

"As we have seen in the past couple of decades in the Deep South, sometimes these tropical features stall and produce torrential rainfall once they make landfall," according to AccuWeather Hurricane Expert Dan Kottlowski.

"Allison did that in 2001 and Harvey did that in 2017," Kottlowski said.

While Harvey was once a major hurricane, Allison peaked as a tropical storm. So a powerful hurricane is not necessary for tremendous rainfall and flooding.

A broad area of moisture alone will cause downpours and localized flooding over parts of the Southeast, including the Florida Peninsula this week even in absence of any tropical depression or storm.

"Residents from western Florida to eastern Louisiana should especially remain alert for an increase in downpours and a heightened risk for flooding later this week and into the start of the weekend," Douty said.

The downpours would spread spread westward, depending on the storm's eventual development and track.

After the system leaves the Gulf of Mexico, its eventual track will determine whether heavy rain aims for the interior South or the threat continues in the Deep South.

With weak steering winds now and into next week, any feature that wanders onshore may not be in a hurry to leave or move well inland.

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 U.S. need to be watched closely for early season development due to water temperatures running above normal.

AccuWeather’s 2019 predictions have not changed since the initial forecast was released on April 3.

Forecasters continue to call for 12 to 14 tropical cyclones this season. Of those, five to seven are predicted to become hurricanes and two to four are predicted to become major hurricanes.

While El Niño conditions may suppress the numbers 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.

This year, AccuWeather will implement its RealImpact™ Scale for Hurricanes to assist with public safety and understanding, as well as risk of damage should a tropical threat arise.

"If the scale was retroactively used, Tropical Storm Allison would have a RealImpact of 4 and Harvey would have a RealImpact of 5, based primarily on flooding rainfall," Kottlowski said.

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. 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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