Invest 92L Brings Rainfall for the Gulf Coast
  • A broad area of low pressure has emerged over the northeastern Gulf of Mexico.
  • This is an area where July tropical storms have formed in the past.
  • A tropical depression or tropical storm is likely to form within the next day or two.
  • Tropical storm, hurricane and storm-surge watches could be required for a portion of the northern Gulf Coast on Wednesday.
  • The future track and intensity of this potential tropical system remain a bit uncertain.
  • Heavy rain leading to flash flooding is a threat along the northern Gulf Coast, dependent on the exact track.

Low pressure in the northeastern Gulf of Mexico is increasingly likely to develop into a tropical depression or tropical storm within the next day or two and then head toward the Gulf Coast this weekend, bringing heavy rain, winds and some coastal flooding, though the exact track of the system remains uncertain.

The National Hurricane Center (NHC) has assigned a 90% chance of tropical development, possibly as soon as late Wednesday or Thursday while the system moves westward across the northern Gulf of Mexico.

This area of interest has been deemed Invest 92L by the NHC. That’s a naming convention used to identify weather systems that could potentially develop into a tropical depression or storm.

(MORE: What Is an Invest?)

Invest 92L

(The potential area of tropical development according to the latest National Hurricane Center outlook is shown by a polygon, color-coded by the chance of development over the next five days. An “X” indicates the location of a current disturbance.)

If the circulation center of this area of low pressure becomes better defined with concentrated shower and thunderstorm activity, then the NHC could deem it a tropical depression or storm by late Wednesday or Thursday.

The NHC mentioned tropical storm, hurricane and storm-surge watches could be required for a portion of the northern Gulf Coast on Wednesday.

An Air Force Reserve Unit reconnaissance aircraft is scheduled to investigate the Gulf low Wednesday afternoon if enough thunderstorms flare up around it that soon.

Recent computer model forecast guidance suggests the area of low pressure should be steered westward or west-northwestward through the northern Gulf of Mexico in the general direction of Louisiana and East Texas. That movement would be induced by the clockwise flow around a high-pressure system centered in the southern Rockies and Plains.

The system would then be drawn inland this weekend somewhere from East Texas into the lower Mississippi Valley through a gap between the aforementioned Plains high-pressure system and an extension of the Bermuda high over the Bahamas and the Florida Peninsula.

(MORE: Where July Named Storms Have Made a U.S. Landfall in the Satellite Era)

Factors steering the tropical system late this week include high pressure aloft centered over the southern Rockies and the Bermuda high. The system should eventually track inland through the gap between the pair of upper-level highs.

The intensity of the system remains uncertain, ranging from either a tropical depression to a tropical storm, which would be named “Barry.” There are a few model solutions which suggest it could even reach low-end hurricane status before landfall this weekend, but that seems to be a small chance at this time.

For now, residents along the Gulf Coast from East Texas to the western Florida Panhandle should simply monitor the forecast, knowing that conditions could change. It’s also a good time to make sure your preparedness kit is ready to go for the rest of hurricane season.

Potential Impacts

Regardless of whether a tropical depression or storm forms, a threat of heavy rain and flash flooding is in play late this week into this weekend somewhere near and inland from the Gulf Coast.

Typically, these types of tropical depressions or storms produce their heaviest rain along and to the east of their tracks. This suggests heavy rain is possible from the upper Texas coast to southern Louisiana, southern Mississippi, southern Alabama and parts of the Florida Panhandle.

How much rain falls depends on how fast the system moves, rather than the intensity of the tropical system itself.

For now, this system does not appear to be the type of stalling tropical cyclone to the magnitude of either Florence in 2018 or Harvey in 2017 that produced prolific rainfall.

However, areas of heavy rain are likely to persist over parts of the Deep South well after the center moves ashore and may persist into early next week.

Rainfall Potential Through Sunday Night

(This should be interpreted as a broad outlook of where the heaviest rain may fall and could shift based on the forecast path of the tropical cyclone. Higher amounts may occur where bands of rain stall over a period of a few hours.)

Onshore winds should eventually lead to dangerous rip currents along parts of the northern and eastern Gulf Coast.

It’s too early to determine the location and magnitude of any impacts from strong winds or storm surge along a portion of the Gulf Coast, as that depends on the exact path and intensity of the tropical system.

(MORE: Where July Named Storms Have Made a U.S. Landfall in the Modern Satellite Era)

What’s Causing This Potential Tropical Development?

Computer forecast models over the past several days have shown that an upper-level disturbance meteorologists call a mesoscale convective vortex (MCV) will move from the Deep South into the northeastern Gulf of Mexico.

These swirling areas a few thousand feet above the ground are produced by thunderstorm clusters. Because they already have spin, moisture and energy, they can occasionally become tropical systems once over water.

If the upper-level system can maintain itself over the northern Gulf of Mexico, it could start the process of developing a tropical depression over Gulf waters that are already warmer than average for early July, with sea-surface temperatures from 84 to 88 degrees.

According to an analysis from the Cooperative Institute for Meteorological Satellite Studies at the University of Wisconsin-Madison, there is no appreciable wind shear over the Gulf of Mexico that could prevent a tropical depression or storm from forming.

(MORE: There’s More Than One Way a Tropical Storm Can Form)

We’ll continue to monitor this forecast in the days ahead, but for now, let’s take a look back at what has happened in July.

Tropics in July

July has accounted for only 8% of the Atlantic hurricane season’s named storms since 1851, according to NOAA’s Hurricane Research Division.

From 1950 to 2018, 67 named storms formed in July, averaging about one named storm in July each year.

(MORE: Typical Tropics in July)

Most tropical depression and tropical storm formation occurs in the Gulf of Mexico and the far western Atlantic over the warm Gulf Stream, particularly in early July.

Development then becomes more common throughout the rest of the Atlantic Basin as July progresses. By late July, development occurs more frequently due to the warmth of ocean temperatures and disturbances, like tropical waves and thunderstorm complexes, instead of old frontal boundaries.

Storm origins in July in the Atlantic Basin.

In the last 15 years, there have been several notable July storms.

July 2018 was unusual since both Beryl and Chris formed into hurricanes during the month. That marked the first time since 2008 that the Atlantic had a pair of July hurricanes.

Over the July Fourth 2014 holiday, Hurricane Arthur raked eastern North Carolina and the Outer Banks with storm-surge flooding and strong winds.

The strongest recent storm to make landfall in the United States in July was Hurricane Dennis, which made landfall in the western Florida Panhandle on July 10, 2005, as a Category 3 hurricane.

Most systems in July stay out to sea, but as you can see above, a few storms, and even hurricanes, can come ashore.

It is best to be prepared every hurricane season before tropical storms and hurricanes develop if you live anywhere near the coast.

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