Hurricane or Typhoon or Tropical Cyclone are different names of similar weather phenomena. Hurricane is region specific term used for severe tropical storm with high speed wind occurring in North Atlantic Ocean including the Gulf of Mexico and the Caribbean Sea; the Northeast Pacific Ocean and the South Pacific Ocean. Hurricanes generally have minimum rotating speed of more than 74 miles per hour. Hurricanes season in the Atlantic, Gulf of Mexico, Caribbean and Central Pacific Basin is usually between 1st of June to 30th November. The hurricane season in the Eastern Pacific Basin is usually from 15th May to 30th November. This terrifying blast of the nature causes great calamities.
Similarities with Tropical Cyclones
Tropical cyclones or Typhoons are other name used for similar tropical storm such as hurricanes, the only difference is their locations. Severe storms in the northwest side of the Pacific Ocean are called typhoons and the term Tropical cyclone is applied for severe storms with strong wind and rain characterized by low pressure centers over warm water of the South West Indian Ocean. Low pressure center, strong winds and spiral band of thunderstorms are common characters of tropical cyclones and hurricanes. The force of hurricane or tropical cyclones decreases when they hit land as a hurricane or tropical cyclone is fueled by warm ocean water, but still causes disaster when enters land with heavy rain and stormy wind before storm dies out completely.
Origin of the term Hurricane
The origin of the term Hurricane has influence of mythology. It is believed that the term Hurricane is derived from the term "Hurican," which is the Carib Indian’s God of Evil. Even the term Hurican is further derived from Hurakan, the Mayan creator of God, believed to have created dry land from chaotic water and then destroyed men of wood with heavy storm and flood.
Physical Structure of a Hurricane
A hurricane has three main parts an eye which is the center of the storm, an eye wall and the spiral rain bands in the outer region. A mature hurricane has winds blowing in roughly circular shape. The eye of a mature hurricane is usually 20 to 30 miles wide, with calmer air and light or no rain. The surface wind of a storm blows inward towards the center. The wind speed increases at the eye wall, which surrounds the eye. The eye wall is characterized by strong rainfall and storm. The spiral rain band, the third important part of the hurricane are long band of clouds spiraling inbound to the eye wall. The rain bands are also capable of producing heavy rain and wind.
Scientific Reasons of hurricane formations
The great temperature difference between the warm water and the overhead cloud triggers the formation of a thermodynamic engine of hurricane. The temperature of the warm water above 26°C creates the energy for the hurricane. The heat of the warm water causes the water to evaporate and create moist air and overhead clouds. The cloud above the warm water surface pulls up the moisture and air from the water surface and creates a low pressure area beneath, which further attracts cooler air from the surrounding high pressure areas. The cooler air then becomes warm coming in close proximity of the warm water surface and continues to rise above. The warm moist air after rising cools off and forms clouds. The whole process of clouds formation and wind speed grows and the storm becomes faster creating a hurricane or cyclone depending on its location.
Hurricanes are formed mainly due to the presence of three prime factors, first warm ocean water, which provide moisture and heat to the overhead air required to fuel the hurricane; second moisture in the atmosphere from evaporation of the ocean water combined with heat energy to form powerful hurricane. Third, a wind pattern is required near the surface of the ocean to spirals air inward, which is required to form hurricane. Besides, some preexisting weathering disturbances in the tropical circulation or even tropical depression can propel a hurricane.
Due to the rotation of the earth on its axis, the storm formed north of the equator rotates counterclockwise and storms at the south of the equator rotates clockwise. Late summer is the time when cyclones or hurricanes occurrence increases, as at this time of the year the difference between sea water temperature and the over lying air is the greatest.
High hurricane risk or prone places in world
The North Atlantic Ocean and the East Pacific Ocean are the hurricane regions, where most of the world’s hurricanes occur. The Atlantic hurricane season is at its peak from mid-August to late October. The Caribbean nations, Mexico and south-east part of USA are more prone to hurricanes. In fact, all of the North Atlantic Ocean, Gulf of Mexico coastal areas, the Pacific coast, the US territories on Pacific, US Virgin Island, Puerto Rico, Hawaii, etc. are high hurricane risk areas.
A hurricane has two types circulation - primary and secondary. The primary circulation of the storm is circular in nature and is the rotational part of the flow. This circulation is influenced by Coriolis force, centrifugal force, pressure gradient and friction and the secondary circulation directs the energy flow of the storm, it moves in vertical and radial direction, it is overturning part of the flow.
The movement of a hurricane is navigated by the global winds and the Beta effect. A hurricane moves along the path guided by its surrounding wind field. For example, Trade winds or the easterly winds in the tropics direct the hurricane towards the west. The other factor influencing the hurricane movement is the "Beta effect" that is the variation of Coriolis force with latitude. The Beta effect drifts the hurricane North Westward.
Dissipation of Hurricanes
Dissipation of hurricane in simple words means disappearance of the storm. Hurricane dissipates when it loses its strength due to natural causes such as when hurricane moves over the land it loses its energy, it was gaining from the warm ocean water and hence the storm dies quickly. Even when the storm moves over colder ocean water with less than 26.5°C temperature, the hurricane loses its strength. Change in wind speed and direction with height that is the vertical wind shear can result in demise of the hurricane. Besides, a hurricane when moves into mid latitude can transform into extra tropical cyclone with weakening of warm center and transition to cold core center.
Effects of Hurricanes
Hurricanes have environmental as well as economic effect. Hurricanes create large waves, causes heavy rainfalls, which results in floods and resultant destructions and casualties. Hurricanes bring along strong gusty winds, which have the potential of destroying vehicles, buildings, bridges, uprooting trees and damaging other structures. Millions of people have been affected by hurricanes and billions of dollars have been spent in hurricane preparedness and also in rebuilding those areas, structures, which are damaged by nature’s fury. Beside, a hurricane when touches the shore carries salt from warm ocean water and increases level of salinity of many freshwater areas consequently affecting many freshwater habitats. Hurricanes also have some positive impact like it maintains global heat balance by taking the warm moist air to mid latitudes and polar areas.
Observation and Forecasting of Hurricanes
Satellites, Land based observation, ship based observation or hurricane hunter aircrafts are tools for hurricane forecasters to predict the path of the storm. Satellites today are the best tools for getting information about the ocean borne hurricanes, which are far from the land based observation network. Even aircraft based observations have also been successful before the advent of the satellites. Agencies like Tropical Cyclone Warning Centers and National Hurricane Center define the future path of the storm by designing computer models from the data drawn from the observation platforms. When the surrounding wind field or the trade winds are stronger, forecasting of the storm path becomes easier for the forecasters.
Classification of Hurricanes
Hurricanes are classified on the basis of their intensity; Tropical disturbance, depression, storm, and tropical cyclone or hurricane. In fact, Tropical disturbance is the first stage of the beginning of a hurricane. It is a low pressure area in the atmosphere with converging wind, which results in the tropical disturbance. Once the system develops with organized circulation center of the wind, it becomes a depression. The depression then turns into tropical storm with increase in the wind speed to about 39mph. The wind speed when intensifies and grows above 74 mph the storm becomes a hurricane over the Atlantic and a typhoon in west of Pacific.
Natural Causes of Hurricanes
The great temperature variance between the warm ocean water and the overlying air activates the birth of a hurricane. The water vapor in the air formed due to evaporation of the warm ocean water also fuels the hurricane because of the latent heat release during condensation process and cloud formation. A cluster of thunderstorms also results in tropical disturbance, which is the beginning of a hurricane. Thunderstorm activities are supported in the atmosphere due to the presence of vertical temperature profile, as the temperature decreases with height.
Man made causes of Hurricanes
In depth analysis of the recent extreme natural disasters reveals, the over exploitation of environment and its resources by people as the main factor behind the disasters. Scientists believe that the increase in the number of strong hurricanes is mainly due to the global warming and resultant increase of the sea surface temperature and rise in the sea water levels, causing hurricanes. Hurricane Katrina of 2005 in US caused immense damage and causalities not because of the strong hurricane only but because of destruction of wetlands, construction of houses, pipelines near the coast in hurricane prone areas, and other human activities, increasing the level of disasters.
Typhoon Bolaven Lashes
Tropical Storm, ISAAC
heads to Florida
Hurricane Sandy Map
Areas Affected by
Typhoon Bopha (Pablo) in Philippines
Last Updated : October 07, 2016