Hurricanes are considered one of our planet’s most amazing meteorological phenomena. Strong winds, great sized clouds and intense storms come together advancing through the ocean and reaching dry land, destroying everything in its path.
Felled trees, building damage, changes in the natural landscape and, in the worst cases, fatalities, are only some of the consequences they can cause, which are mostly unpredictable.
Many times, due to the great intensity they reach, with winds that surpass 300 kilometers per hour, they are catalogued as real natural disasters. There have been hurricanes recorded that caused devastation similar to an earthquake or atomic bomb in little time. Estimates even say that the energy released during the occurrence of this phenomenon is so great that it could be compared to the energy released by ten bombs like the one dropped n Hiroshima.
Entire towns disappeared under the strength of the impetuous winds, which can be monitored by the technology created by human beings.
To this day, no device can counter its strength; Man has become a mere spectator of what takes place each time a hurricane develops.
Origin of a hurricane
Hurricanes are high intensity winds formed in the ocean mainly due to the difference in pressure between two masses of air.
They occur at low latitudes, especially in tropical areas, where the necessary conditions for their surge and growth are present. They rarely surpass the heights of some forms of relief (like plateaus or mountains) and they quickly lose energy as they go through the continent.
In order to understand how this extraordinary phenomenon is generated we must consider the necessary presence of four elements:
– Temperature of the ocean: the water in the ocean must reach a temperature of over 27ºC, which makes it easier for the humid air to heat up, expand and begin to ascend. The increase in temperature then eases the evaporation of water and its later condensation, to such a degree that huge storm clouds are formed.
– Environmental humidity: it must also be abundant to grant the forming hurricane energy. This contributes in explaining why hurricanes lose strength when they reach dry land, as the humidity they feed of in the ocean decreases.
– Winds: the ease evaporation and cause negative pressure that drags the air towards the center and top of the hurricane, sucking in more hot air and energy from the surface of the ocean.
– The Earth’s rotation: although it affects all our planet’s phenomena, in the case of the hurricane it grants it the ability to spin and move from the oceans to firm land, like a real top. In addition, depending on the hemisphere, the direction the winds take is also an influential factor (in the northern hemisphere they go counter clockwise, while in the southern hemisphere they go the opposite way).
It is possible to distinguish four stages during the formation of a hurricane, which are told apart by the intensity of the winds. They are:
– Tropical disturbance: a hurricane is born from this phenomenon, which basically consists of the formation of a low pressure center. Light winds are generated over the surface of the oceans. The formation of a few clouds begins.
– Tropical depression: winds reach speeds of nearly 60 km/h and begin to spin in a circular pattern.
– Tropical storm: it corresponds to the development of the phenomenon, because the winds continue to increase in speed steadily (between 60 and 100 km/h). It is possible to detect an incipient eye of the hurricane, with its characteristic circular shape.
When the cyclone reached this intensity, it is given a pre-established by the World Meteorological Organization .
– Hurricane: when the storm intensifies, we can now speak of the presence of a hurricane. The maximum winds can surpass 119 km/h and the clouds cover an extension that goes from 500 to 900 kilometers in diameter, causing intense rain.
The eye of the hurricane normally reaches a diameter that varies between 24 and 40 kilometers; however, it can reach 100 kilometers. At this stage, it is also possible to classify it in one of the categories of the Saffir-Simpson scale (see further ahead).
When the hurricane reaches dry land, it loses its energy until it dissipates.
The eye of the hurricane
Thanks to the photos taken from planes and ever more advanced shots delivered by meteorological satellites, it is possible to differentiate some zones present in all hurricanes.
The most well-known of them is the center, commonly dubbed the eye of the hurricane. It is a very quiet circular area, with no clouds, scarce or no rain and winds that do not surpass 30km/h.
When it passes over a spot, it grants a limited calm to the hurricane winds; its duration is no longer than an hour, depending on its extension.
The eye of the hurricane measures approximately between 25 and 35 kilometers and serves as a real rotation axle for the winds. The lowest pressure is recorded at ground level, and at the top part of the hurricane, the temperature is warmer. Regarding this last point, it has been demonstrated that said temperature can be up to 10ºC higher than the surrounding environment.
At the outer limit of the eye there is a zone of vertical clouds (cumulonimbus) that are heavily loaded with water, which stretches from 150 meters to 15 kilometers high. It is known as the walleye and is characterized for having the strongest winds and most intense rain.
Next, always towards the outside of the hurricane, is a great extension of cloudy formations where the strong rain zones move like a spiral towards the center, without going through the wall.
For many years, the name of hurricanes in the Atlantic zone depended on the saint that was celebrated on the same day it had been formed or observed for the first time. Later, Australian Clement Wragge named them according to a very arbitrary list of female names, as they only included the names of people he disliked.
During the Second World War, an alphabetic code was used that eased the transmission of this information between troops (with names like Alpha, Beta, Charlie, etc.). Based on this order, in 1953, the United States Meteorological Service once again granted hurricanes female names; however, in 1978 a feminist organization filed a complaint, petitioning the inclusion of male names as well.
It is so how from that day on, the World Meteorological Organization put together six lists with male and female names, from the letter A to the letter W, which are common in Spanish, English, and French. These lists are cross-referenced each year, which explains why, in 2007 for example, the same list is used as in 2001.
There is only one rule for the withdrawal of some names. If the hurricane caused great economic and social impact for the country or countries it passed through (causing extreme damages and a great amount of deaths), it is eliminated from the lists. This happened with Andrew, Katrina, David and Hugo.
In 1969, the United Nations petitioned the evaluation of damages caused by the passing of hurricanes through a specific type of housing. From this, American engineer Herber Saffir and the then director of the National Hurricane Center of the United States Robert Simpson developed a measuring scale to classify the potential damage a hurricane can cause, considering minimum pressure, winds and the tide after its wake.
It is made up of five categories:
– Category 1: the damage caused by these hurricanes is minimal. Winds only reach speeds that go from 119 to 153 kilometers per hour, while the ocean swells do not go over 1.5 meters. Among the most visible disorders are the felling of some branches belonging to small trees, as well as the collapse of some structures that were not reinforced well.
– Category 2: it causes moderate damage, as winds can go from 154 to 177 kilometers per hour and ocean swells can easily reach up to 2.4 meters. It knocks down some trees, damages signs and advertisement and partially destroys roofs, doors and windows. It is also possible for highways, roads and constructions near the coast to flood due to the rising of the waters.
– Category 3: winds between 178 and 209 kilometers per hour and swells of over 3.5 meters cause extensive damage. Trees that are several meters tall and with firm roots fly are lifted through the air, while mobile homes are easily removed from their habitual places. In addition, the great constructions of the coastal strip suffer serious deterioration due to the increase in water level and the amount of debris that crashes into them dragged by said waters. If a hurricane of these characteristics is detected, it is probable that there will be an evacuation of the people that live in the areas nearest to the sea, moving them to more inland sectors.
– Category 4: extreme damages. The winds go from 210 to 250 kilometers per hour, and the swells surpass five meters in their advance towards dry land. The total collapse of roofs is produced; some walls cave in and the low lands are flooded. The water from the coast easily advances some ten kilometers inland, which causes the urgent evacuation of the population.
– Category 5: hurricanes of this rank are considered devastating. Winds reach speeds of over 250 kilometers per hour and swells surpass the 5.4 meters of the previous category. An almost complete collapse of the constructions, vegetation and even evacuation routes is produced in areas hit by hurricanes that belong to this category.