Tropical or Subtropical Development Likely in Gulf of Mexico Early This Week; Heavy Rain and Flood Threat Expected Along Gulf Coast

June 19,2017
The Gulf of Mexico is being monitored closely for the potential development of a tropical or subtropical depression or storm early this week. A threat of heavy rain and flooding is likely to develop along parts of the U.S. Gulf Coast this week regardless of the intensity and track of this system.
Current satellite imagery shows vigorous shower and thunderstorm activity in the northwestern Caribbean and the eastern Gulf of Mexico in association with a broad area of low pressure in the southern Gulf of Mexico.
(MORE: Hurricane Central)

Gulf of Mexico and Caribbean Infrared Satellite

The National Hurricane Center (NHC) has dubbed this system Invest 93L and says it has a high chance of developing into a tropical or subtropical depression or storm. A Hurricane Hunter investigative flight into Invest 93L has been tentatively scheduled for Monday.
(MORE: What Is An Invest?)
A well-defined low-pressure system is needed for a tropical/subtropical depression or storm to organize, and that hasn't happened yet. Impacts will likely be the same for the Gulf Coast even if it remains a broad low-pressure system.
In the near term, heavy rainfall from Invest 93L will affect portions of Central America, the Yucatan Peninsula, Jamaica, the Cayman Islands and western Cuba.

U.S. Threat: Heavy Rain, Flooding Along Gulf Coast

Most of the forecast guidance suggests the area of low pressure will track in a north or northwest direction through the Gulf of Mexico early this week. As this occurs, parts of the U.S. Gulf Coast and Florida will see abundant moisture from southerly winds on the eastern flank of the low, which will fuel heavy rainfall.
Another ingredient in this soaking setup is a stalling frontal boundary in the South that will also provide a focus for locally heavy rain.

Abundant moisture will fuel heavy rain along the Gulf Coast on the northern and eastern side of where the low tracks.

Florida is the first area to experience this influx of moisture, resulting in heavy downpours into Monday. Parts of the northern Gulf Coast will see heavy rain Tuesday through Thursday.
This heavy rain could eventually lead to flash flooding and river flooding in some areas.
It should be noted that the majority of the rain will be on the northern and eastern side of the low-pressure system and could affect areas well away from its center. Also, the impacts from this system will occur even if it never becomes a tropical or subtropical depression or storm.
What To Know

• The heaviest rain amounts are likely to be on the northern Gulf Coast, including parts of Louisiana, southern Mississippi, southern Alabama and the western Florida Panhandle.
• This swath could see 5 inches or more of total rainfall. Locally extreme rain amounts of 10-16 inches could occur depending on how the weather pattern evolves this week, according to the National Weather Service in New Orleans.
• Flash flooding and river flooding are both possible threats.
• Other parts of the South, including the Florida Peninsula, will also see locally heavy rain at times this week due to the abundant moisture and stalling front. Heavy rain could occur as far west as southeast Texas later this week.
• Timing begins as early as Tuesday and continues through Thursday, possibly lingering into Friday.
• A high risk of rip currents is likely along parts of the Gulf Coast. High surf and some coastal flooding are also expected.
• Gusty winds are likely near parts of the northern Gulf Coast this week, particularly north and east of where the low tracks.
• If this system does develop into a tropical depression or storm, it is not expected to rapidly intensify and is unlikely to reach hurricane strength.

Rainfall Potential Through Thursday

Again, there is still uncertainty with regards to where the low will track in the Gulf. The track of the low will dictate exactly where the heaviest rain will occur in addition to coastal flooding and rip current risks.
(MORE: Florida's Drought Has Been Reduced by 60 Percent in Just Two Weeks)
This system may also be subtropical in nature, meaning it would have characteristics of a tropical and non-tropical low. Either way, the majority of the impacts will be the same.

June's Typical Formation Areas

The western Caribbean and Gulf of Mexico are two of the areas we typically look for the development of tropical storms in June.

This map shows the typical formation areas and tracks for named storms in June.

Any storms that do form typically track north or northeastward, which brings the Gulf Coast and the Southeast coast in play for potential impacts.
On average, there's one named storm in June in the Atlantic, Caribbean or Gulf of Mexico every one to two years.
Last June was an outlier, when Bonnie, Colin and Danielle all spun through the Atlantic Basin as tropical storms.
(MORE: What to Expect During June)
MORE: Atlantic Basin Retired Hurricanes and Tropical Storms

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