The Atlantic hurricane season is entering one of its most important periods, and meteorologists are already watching the skies off the coast of West Africa.
The U.S. National Hurricane Center is currently monitoring two separate areas of disturbed weather in the tropical Atlantic.
Neither is a tropical storm or hurricane yet, and there is no immediate indication that either system poses a threat to the United States.
But both are developing in a part of the Atlantic that meteorologists watch particularly closely at this time of year.
One disturbance is already several hundred miles west-southwest of the Cabo Verde Islands, while another tropical wave is expected to move off the west coast of Africa early this week.
The first has a 20% chance of developing into a tropical cyclone during the next seven days, while the second has a 50% chance of formation over the same period, according to the latest NHC outlook. For now, there is no reason for people in the Caribbean or the United States to panic.
The significance of these systems is that they are appearing in one of the world’s most important hurricane-producing regions – and August is when the Atlantic begins to become much more active.
This Is Where Hurricanes Can Be Born
The waters around West Africa may seem a long way from Florida, the Caribbean and the U.S. East Coast. Meteorologically, however, they are closely connected.
Many Atlantic hurricanes begin as tropical waves – elongated areas of low pressure associated with thunderstorms that move westward across Africa and then emerge over the tropical Atlantic.
Some of these waves dissipate within days. Others encounter a combination of warm ocean water, moisture and favourable atmospheric winds that allows thunderstorms to become increasingly organised.
If the circulation becomes sufficiently organised and sustained, a tropical depression can form. It can then strengthen into a tropical storm and, eventually, a hurricane.
The systems that develop close to the Cabo Verde Islands are known as Cape Verde-type disturbances or hurricanes, and they are particularly important because they can have a very long stretch of warm ocean over which to intensify.
NOAA notes that the Cape Verde season generally begins in August and that these storms can become among the longest-lived and most intense systems of the Atlantic season.
Why Meteorologists Are Watching These Two Systems
The word “disturbance” can sound alarming, but it does not mean that a hurricane is forming. At this stage, forecasters are looking for several ingredients to come together.
The first is warm water. Tropical cyclones draw much of their energy from warm ocean surfaces. The deeper the warm layer extends, the more energy can potentially be available to a developing system.
The second is moisture. A tropical cyclone needs large amounts of moist air and thunderstorms around its centre.
The third is perhaps one of the most important: wind shear. Strong winds blowing in different directions or at different speeds at different altitudes can tear a developing storm apart before it has a chance to organise.
Forecasters therefore watch satellite images, atmospheric measurements and computer models to determine whether the environment around each disturbance is becoming more or less favourable.
The First Disturbance Has Already Crossed Into the Atlantic
The first system is a broad area of showers and thunderstorms associated with a tropical wave located several hundred miles west-southwest of Cabo Verde.
The NHC says some gradual development is possible during the early to middle part of the week as the system moves westward across the central tropical Atlantic.
However, upper-level winds are expected to become less favourable later in the week as the system approaches the Lesser Antilles. That is why the current seven-day probability remains relatively low at 20%.
In other words, meteorologists see something worth watching – but not yet something that resembles a hurricane.
The Second Wave May Be More Interesting
The second system is still closer to Africa. The NHC expects another tropical wave to move off the west coast of Africa early this week.
Unlike the first disturbance, the atmospheric conditions farther east are currently expected to be favourable enough for gradual development later in the week.
The NHC currently gives this system a 50% chance of becoming a tropical depression or stronger tropical cyclone within seven days.
That probability can change quickly. Tropical systems are notoriously difficult to forecast before they develop a well-defined circulation, and a 50% formation probability should not be interpreted as a 50% chance of a hurricane hitting a particular location.
It simply describes the likelihood that the system itself will develop into a tropical cyclone.
Why August Matters
The timing is important. The official Atlantic hurricane season runs from June 1 through November 30, but activity is far from evenly distributed across those six months.
The Atlantic typically becomes much more active in August, with the seasonal peak arriving around September.
According to NOAA’s hurricane climatology, about 96% of major Atlantic hurricane days occur during August through October, with the overall peak of activity around early to mid-September.
That means forecasters are now entering the part of the year when disturbances emerging from Africa deserve particular attention.
The Sahara Plays a Role Too
There is another unusual feature of this region that scientists watch closely: the Saharan Air Layer.
Huge quantities of hot, dry and dusty air periodically move westward from the Sahara over the tropical Atlantic.
This dry air can suppress thunderstorms and introduce strong atmospheric stability into an environment where tropical cyclones are trying to develop.
African dust therefore acts as one of several natural obstacles that can prevent tropical waves from becoming storms.
But when a tropical wave moves into a region with less dry air, sufficient moisture and favourable wind conditions, its prospects can change.
This is one reason the same disturbance can appear relatively harmless on one day and considerably more interesting to forecasters several days later.
Not Every Tropical Wave Becomes a Hurricane
This is perhaps the most important point. Africa produces numerous tropical waves every year. Only a fraction become tropical depressions. An even smaller number become tropical storms, and fewer still develop into hurricanes.
The Atlantic atmosphere is a constant competition between processes that help storms grow and processes that tear them apart.
A disturbance needs to maintain a coherent circulation while producing enough persistent thunderstorms to lower pressure and strengthen its winds.
That is why meteorologists do not simply look at whether a cloud mass appears large or impressive on satellite imagery. They are looking for structure.
From Africa to the Caribbean
A tropical wave that successfully develops near West Africa can travel thousands of kilometres across the Atlantic.
The prevailing trade winds generally carry these systems westward or west-northwestward.
Some eventually approach the Lesser Antilles and Caribbean. Others turn north before reaching land.
Some weaken completely over the ocean. And some can continue toward the Bahamas, the U.S. East Coast or the Gulf of Mexico.
The exact path depends on the atmospheric steering currents surrounding the storm.
That means the appearance of a disturbance near Africa does not mean that the United States is about to be hit. In fact, at this stage, the eventual track of either system is highly uncertain.
What Scientists Are Looking For Now
For forecasters, the next several days are about watching whether the ingredients begin to align. They will be looking for:
– A stronger, more organised circulation.
– Persistent thunderstorms near the centre of the disturbance.
– Falling atmospheric pressure.
– Favourable wind shear.
– Warm ocean temperatures.
– A track that allows the system to remain over open water.
Satellites are particularly important because much of the eastern tropical Atlantic is far from land-based weather stations.
Modern satellite observations allow forecasters to estimate cloud structure, atmospheric moisture, ocean temperatures and other characteristics in near real time.
NOAA says satellite observations are essential for monitoring tropical cyclones and the environmental conditions that influence their formation, movement and intensity.
The Quiet Before the Peak
For now, the Atlantic remains relatively quiet compared with what it can become later in the season. There are no active tropical cyclones in the Atlantic basin at the moment.
But the appearance of two disturbances near the African coast is a reminder that the season is entering a more important phase. One system may weaken. The other may never develop beyond a tropical wave.
Or the atmosphere could eventually provide one of them with exactly what it needs to become a named storm. That is why meteorologists are watching.
Not because a hurricane is already coming – but because some of the Atlantic’s most consequential hurricanes begin looking almost exactly like this: a cluster of thunderstorms emerging from the African coast, crossing warm tropical waters, and gradually discovering whether the atmosphere will allow them to grow.
Sources:
- National Hurricane Center (NHC) – current Atlantic Tropical Weather Outlook, including the two disturbances and their seven-day formation probabilities.
- NOAA / National Hurricane Center – hurricane climatology, seasonality and the Cape Verde region’s importance in August.
- NOAA NESDIS – explanation of how satellites are used to monitor tropical cyclone formation and development.
- NOAA Climate Prediction Center — extended tropical cyclone outlooks and monitoring of African easterly-wave activity.
