As hurricane season ramps up, meteorologists begin to look off the coast of Africa for tropical development.

Called tropical waves, these disorganized clumps of storms can develop into some of the strongest storms of the season that can impact the Caribbean and the Eastern U.S.

The importance of tropical waves

Often called African easterly waves, tropical waves are the building blocks for much of the tropical storm and hurricane activity in the Atlantic Basin. They can even contribute to activity in the Pacific as well.

In fact, most hurricanes eventually develop from these disorganized lines of showers that cross the Atlantic, starting back by eastern Africa.

Tropical waves are a reason why the bulk of named storm formation in August, the reds and purples on the map below, are located where they are. They have miles of warm oceans to traverse, plenty of time to get organized and potentially get a name from the National Hurricane Center.

A disclaimer: These are not waves in the ocean in the sense that wash up on the shore and destroy your sand castle. These tropical waves exist from near the surface to about 10,000 feet above the ocean, drawing their strength from the warm waters of the ocean.

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According to the National Hurricane Center, 60 tropical waves track across the Atlantic Ocean each year. An impressive 85% of major hurricanes (Category 3 or higher) start as a tropical wave from Africa.

Roughly one in five of these tropical waves becomes an Atlantic Basin tropical cyclone, and a few of these waves travel into the eastern Pacific before reaching a tropical storm or a hurricane.

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How they are made

Tropical waves begin as energy and rotation in the atmosphere that form over northern Africa. This area is perfect for the formation of these waves because you have clashes in temperature along a boundary of cool, humid air over forested areas of the Gulf of Guinea and central Africa and hot air over the Saharan Desert, which the graphic below shows.

This process is similar to when cold fronts gain energy from the clashing cold Canadian air and the warm, moist air from the Gulf in the U.S.

The clash in these air masses really becomes drastic in the summer, when the Saharan Desert really heats up. Then a westward-moving ribbon of air in the upper atmosphere, called a jet stream, ramps up and steers the waves off the coast of Africa into the Atlantic.

The number of these waves actually peaks in July when the temperature contrast is highest in Africa. There are about 10 waves per month. But we see more successful outings of these waves crossing the Atlantic in August because the environmental conditions improve.

The trek commences

After winds steer these waves into the Atlantic, yet another force acts on them. This you may have heard of: the Bermuda-Azores High.

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These waves often move east to west along the clockwise rotation of the high, being moved into the central Atlantic. It usually takes one to two weeks for waves to successfully cross the Atlantic, but unfavorable conditions can snuff out many of these waves before they ever develop.

Early-season waves actually don't contain much, if any, thunderstorms because the Saharan Desert's dry air mixes in.

But July through September, we start to see thunderstorms associated with these waves, which means we see a greater chance of development.

Tropical waves are tracked on satellite imagery through Africa and across the Atlantic using specialized "Hovmöller Diagrams" (seen above) that make it easy to follow them from east to west.

The structure of these waves

Tropical waves with active thunderstorms often look like an inverted or upside-down "V," especially as they develop further. A small rain band may exist on the western side of a tropical wave, with a much stronger and broader band on the eastern side.

Tropical waves are watched by the National Hurricane Center (NHC) and can be investigated using specialized tropical models and satellite imagery. Development probability and the chance of tropical cyclone formation are diagnosed by the NHC every six hours during hurricane season.

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Without a satellite loop, you may not know a tropical wave is approaching. Ahead of a mature tropical wave approaching the Caribbean islands, for instance, the weather is generally fine; falling surface barometric pressure would be your only clue, as air generally sinks ahead of a tropical wave.

Once the wave axis passes – in other words, surface pressure bottoms out – winds shift out of the southeast and showers and thundershowers pick up.

In the early stages of a tropical wave over the eastern Atlantic, some clouds and showers can overlap over the wave axis. Generally speaking, however, the rain is on the eastern side of the tropical wave.

Tropical waves can bring flooding rains and gusty winds to the Caribbean islands and Central America. Tropical waves often move at 10 to 20 mph, but can move faster.

These waves need to survive dry air, fast upper-level winds and the elevated terrain of the Caribbean islands before they can impact the United States. Only tropical waves in near-ideal conditions can become hurricanes.