Tropical Update: Monitoring Five Areas Across The Atlantic For Development

What you need to know:
– No immediate tropical threats face the Lesser Antilles and Trinidad and Tobago over the next 5 days.
Interests in the Leeward Islands should pay close attention over the next week to a tropical wave that is yet to move off the African coast.
– Those residing in eastern Mexico, the Texas Gulf Coast, and Louisiana should monitor the progress of Invest 94L closely as heavy rainfall is likely through the next several days, regardless of development.
– Those residing in the Cabo Verde Islands should monitor the progress of Invest 93L as heavy rainfall will impact the region through Sunday.

Invest 94L

Tropical Weather Outlook as of 8:00 PM Saturday 11th September 2021

We’ve been monitoring a strong tropical wave, and an upper-level trough interacts across Central America, now moving into the Gulf of Mexico.

Invest 94L is expected to move offshore into the Bay of Campeche later this weekend, then move slowly northward across the western Gulf of Mexico toward Texas early next week. Wind shear will remain a strong 15-25 knots throughout the period. The European and GFS model ensembles strongly suggested that the shear and 94L’s proximity to land will likely hinder any dramatic tropical development. However, some modest strengthening 94L can be expected; given the very moist atmosphere around 94L (mid-level relative humidity around 80%) and the hot sea surface temperatures, it will traverse (around 29°C).

Scattered showers and thunderstorms associated with Invest 94L across the Yucatán Peninsula, entering the Bay of Campeche. (Weathernerds)
Scattered showers and thunderstorms associated with Invest 94L across the Yucatán Peninsula, entering the Bay of Campeche. (Weathernerds)

Currently, Invest 94L is experiencing moderate to strong wind shear from the southwest, taking its large cloud canopy across the Gulf of Mexico.

In their 8:00 PM AST Tropical Weather Outlook, the National Hurricane Center continues to give Invest 94L high chances for tropical cyclone development.

From the National Hurricane Center’s Tropical Update, “A tropical wave and an upper-level trough continue to produce a large area of disorganized showers and thunderstorms over portions of southeastern Mexico and the southern and central Gulf of Mexico. Upper-level winds are gradually becoming more conducive for development, and a tropical depression is likely to form on Sunday or Monday while the disturbance moves northwestward and then northward near the coast of northeastern Mexico. Additional development will be possible through the middle of next week if the system remains over water, and interests along the western and northwestern Gulf coast should monitor the progress of this system. An Air Force Hurricane Hunter aircraft is scheduled to investigate the system tomorrow, if necessary.”

The NHC also adds, “Regardless of development, this disturbance will continue to produce heavy rain across portions of southern Mexico, including the western Yucatan Peninsula, through tonight, which may lead to flash flooding and mudslides. By late Sunday, heavy rain is expected to reach portions of the Texas and Louisiana coasts with a heavy rain threat, then continuing across those coasts through the middle of next week. Localized significant rainfall amounts are possible, potentially resulting in areas of flash, urban, and isolated river flooding.”

7-day rainfall forecast from 8 a.m. Saturday, September 11, 2021, to Saturday, September 18. Specifics of timing and location will vary depending on the track of 94L. (NOAA/NWS Weather Prediction Center).
Specifics of timing and location will vary depending on the track of 94L—7-day rainfall forecast from 8 AM Saturday, September 11th, 2021, to Saturday, September 18th. (NOAA/NWS Weather Prediction Center).

Of the five areas being monitored across the Atlantic, this system has the highest chances of development. According to the NHC, Invest 94L has a high chance, 90%, of tropical cyclone formation over the next 48 hours and a high chance, 90%, of tropical cyclone formation over the next five days. The next name on the list of names for the 2021 Atlantic Hurricane Season is Nicholas.

Invest 93L

Tropical Weather Outlook as of 8:00 PM Saturday 11th September 2021

Tropical Wave 46 in the far eastern Atlantic Ocean is being monitored for tropical cyclone development, presently southeast of the Cabo Verde Islands.

Invest 93L/Tropical Wave 46 is located in an area with somewhat favorable low-level convergence, marginally favorable upper-level conditions, and light to moderate wind shear. However, strong to very strong wind shear exists just north of the low-pressure area with the greatest spin.

Wind shear will be light to moderate (5-10 knots) through Sunday, and sea surface temperatures of around 27°C will support gradual development.

As it heads mainly northwestward close to latitude 16°N, 93L will encounter intensifying wind shear, especially by midweek, and it will not reach dramatically warmer water over this period. Even if it does develop, the most likely outcome is that 93L will weaken later next week, as suggested by most European and GFS ensemble model members.

Tropical Wave 46/Invest 93L moving across the Cabo Verde Islands, producing a cluster of showers and thunderstorms. (Weathernerds)

In their 8:00 PM AST Tropical Weather Outlook, the National Hurricane Center now gives Invest 93L medium chances for tropical cyclone development over the next five days.

From the National Hurricane Center’s Tropical Update, “Showers and thunderstorms remain poorly organized in association with a tropical wave located near the Cabo Verde Islands. Environmental conditions are currently conducive for development, and a tropical depression could still form this weekend or early next week while the system moves westward over the far eastern Atlantic. By the middle of next week, stronger upper-level winds and marginally warm ocean temperatures are expected to limit additional development. Regardless of development, this disturbance is likely to bring gusty winds and locally heavy rain across the Cabo Verde Islands tonight.”

Of the 4 areas being monitored across the Atlantic, this system has the second-highest chances of development. According to the NHC, Invest 93L has a medium chance, 50%, of tropical cyclone formation over the next 48 hours and a medium chance, 50%, of tropical cyclone formation over the next 5 days. The next name, after Nicholas, on the list of names for the 2021 Atlantic Hurricane Season is Odette.

Three More Tropical Threats Elsewhere

A non-tropical area of low-pressure producing scattered showers and thunderstorms. (Weathernerds)
A non-tropical area of low-pressure producing scattered showers and thunderstorms. (Weathernerds)

A third disturbance is also being monitored in the northeastern Atlantic. According to the NHC, “A non-tropical area of low pressure is located over the far northeastern Atlantic several hundred miles northeast of the Azores. This system is forecast to move south-southeastward towards warmer waters, which could allow the low to gradually acquire some tropical or subtropical characteristics by the middle of next week.” This disturbance has a low chance, 10%, of tropical cyclone formation over the next 48 hours and a low chance, 20%, of tropical cyclone formation over the next 5 days.

Tropical Wave 46 (Invest 93L) over the Cabo Verde Islands along 23W, while Tropical Wave 47 along 8W is forecast to emerge in the Atlantic, with medium chances of development over the next 5 days. (Weathernerds)
Tropical Wave 46 (Invest 93L) over the Cabo Verde Islands along 23W, while Tropical Wave 47 along 8W is forecast to emerge in the Atlantic, with medium chances of development over the next 5 days. (Weathernerds)

Another system to watch is already evident as a strong tropical wave over Africa. This wave is likely to emerge into the eastern Atlantic tropics early next week at a lower latitude than 93L, which will give it a better chance of long-term strengthening.

According to the NHC, “Another tropical wave is expected to move off the west coast of Africa in a few days. Gradual development of this system is possible thereafter, and a tropical depression could form by the middle of next week while it moves westward across the eastern tropical Atlantic Ocean.”

This fourth disturbance is has a low chance, near 0%, of tropical cyclone formation over the next 48 hours and a medium chance, 40%, of tropical cyclone formation over the next 5 days, between Tuesday and Friday.

For the Lesser Antilles, this is the system longer-range models indicate could near the Leeward Islands by next weekend, possibly recurving into the Atlantic Ocean. Given this between the 7-10 day time frame, there is significant uncertainty on this system’s eventual track and intensity.

Tropical Weather Outlook as of 8:00 PM Saturday 11th September 2021

Near the southeastern Bahamas, a fifth disturbance may take shape next week. If so, it will most likely be heading toward the U.S. East Coast. Multiple long-range runs of the GFS model have shown a developing system reaching the mid-Atlantic toward the end of next week, although the European model has been less emphatic.

According to the NHC in the 8:00 PM Tropical Update, “An area of low pressure is expected to form near the southeastern Bahamas in a few days resulting from moisture by a tropical wave interacting with an upper-level trough. Gradual development of this system is possible thereafter as it moves northwestward across the western Atlantic.” This fourth disturbance is has a low chance, near 0%, of tropical cyclone formation over the next 48 hours and a low chance, 30%, of tropical cyclone formation over the next 5 days, between Tuesday and Friday.”

But this model shows…

Individual model runs are just one possible outcome from a myriad of outcomes. Weather does not always follow what is modeled, and even what may be forecast. Beware of individual model runs being posted on social media.

Always check the National Hurricane Center for the latest information for tropical cyclones and your local meteorological offices for country-specific advisories.

What should I do?

Don’t panic. There are no immediate or direct tropical storm threats heading to T&T and the Lesser Antilles, so feel free to ignore the “storm coming” chain messages that pass through WhatsApp every hurricane season.

If you are a risk-averse person, now is a good time to check your inclement weather, flood, or hurricane season plan, ensuring your preparedness supplies are not expired, stocked, and in a safe location.

The Office of Disaster Preparedness and Management has compiled a comprehensive guide for preparing for the Wet and Hurricane Season.

Tropical Cyclone Climatology

2021 has already produced 13 tropical storms in the Atlantic Basin, with the next system being named Nicholas for the 2021 Atlantic Hurricane Season. For this time of year, most systems form in the Caribbean, the Gulf of Mexico, and off of the Eastern United States.

As we head through the second half of August, we monitor tropical waves east of the Lesser Antilles.

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