The Making of a Hurricane Over the Atlantic

The Making of a Hurricane Over the Atlantic

By The Hurricane Watch Group

July 18, 2022 4:26 P.M

hurricane dorian
Hurricane Dorian in 2019
Roseau, Dominica (TDN)

Although we can’t see it, there are gases everywhere in the Earth’s atmosphere.  In other words what we refer to as ‘air’ really comprises of gas molecules. These gas molecules are weighted. In fact scientists have calculated that these gases has a combined weight of 5.5 quadrillion tons. The gas molecules closest to the earth are compressed by the weight of the air above them (thanks to gravity).

These gases weighed down by gravity exerts ‘pressure’. It’s estimated that about 14.7 pounds of air press on every inch of our body. It is important to note that the air closest to us (earth) is always much warmer compared to air higher in the atmosphere. That’s because the atmosphere is mostly heated by the land and the sea, and not by the sun.

This air, however, is not evenly distributed across the Earth’s surface. Some areas have more pressure than their surroundings, and some areas have less. Those areas with more pressure are referred to as high pressure systems and those with less as low-pressure systems.

In high-pressure systems, because there is more air than their surroundings, they will constantly push air in an outward direction. These systems are generally associated with clear blue skies.

A key feature of low pressure systems is that they draw (suck) air into them as nature attempts to equalize the air pressure. The air then rises in the atmosphere and the water vapor within it condenses, forms clouds and very often precipitation. Low pressure systems therefore, generally creates bad weather. Hurricanes for example are always associated with low pressure systems.  

For hurricanes to form however, they require warm, tropical regions where the water is at least 27 degrees Celsius or 80 degrees Fahrenheit.  Hurricanes also requires a lot of moisture and converging equatorial winds. This moisture is readily obtained from the rising warm air from the ocean’s surface.

During the Atlantic hurricane season, which runs from 1 June to 30 November each year (when the water is at its warmest), low pressure systems that usually creates thunderstorms over West Africa will drift westward over the warm, tropical Atlantic ocean waters.

The converging equatorial winds will produce the general westward direction away from the coast of Africa and towards the islands in the Lesser Antilles. At the same time the rising water vapor from the sea will provide the energy to  feed the growing storm.  

The first stage of development is usually as a tropical disturbance, which then becomes a depression, then a storm (winds of at least 39 mph), and eventually a hurricane (winds of at least 74 mph). 

While the strength of a hurricane is usually determined by the amount of energy it is able to absorb, its direction very often depends on the positioning of a high pressure system viz-a-viz the hurricane.The Winds within a high pressure system swirls away from the low pressure system, which serves to steer it in a given direction.

Finally, the  measure of air pressure within a storm (also known as barometric pressure) is a good indicator of whether the storm will worsen. Normal pressure at sea level is 1013.3 millibars (Mbs) or 29.92 inches of mercury. As the pressure drops the storm generally increases in intensity.

Within hurricane Maria, a category five hurricane, which devastated Dominica in 2017, the atmospheric pressure dropped to 908 millibars.

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