Hurricanes are powerful meteorological occurrences that feed off the heat of tropical oceans to fuel their rage. These severe storms develop over the ocean, frequently as a tropical wave—a low-pressure system that sweeps over the damp tropics, potentially boosting shower and thunderstorm activity. Sometimes called "twisters" of the ocean," hurricanes can be deadly if they strike land. In fact, hurricanes are one of the most common causes of death in tropical countries.
Tropical depressions are less intense than tropical storms or hurricanes and are usually not considered major weather events. However, occasionally they may produce heavy rain and high winds that cause damage when they move ashore.
Tsunamis are waves caused by underwater landslides or other marine phenomena. They occur in oceans around the world, but are most frequent in coastal areas near active tectonic plates. Although tsunamis can travel far from their source, only small islands are sometimes affected. Because they are driven under water, tsunamis cannot reach land with their energy. But once under water, they can cause widespread damage by flooding inland watersheds and causing debris flows. Debris flows are large volumes of rock, mud, and other solid materials that are released when an area of land is deformed by earthquakes or volcanic eruptions.
Typhoons are strong winds associated with tropical cyclones (storms with a rotating circulation pattern of air surrounding a region of low pressure).
Hurricanes form over the warm tropics' ocean water. When warm, wet air rises over the sea, it is replaced by colder air. The colder air will then begin to warm and ascend. If there is enough warm water, the cycle will continue, and storm clouds and wind speeds will increase, resulting in the formation of a hurricane.
The main cause of hurricane development is the presence of high atmospheric pressure systems (anticyclones). These are large-scale features of the Earth's atmosphere that influence the distribution of weather across the planet. Cyclonic (or anti-clockwise) winds are found within these systems, while direct hits from a cyclone's center would bring about a typhoon. A cyclone can also be defined as a rotating mass of air having winds in one direction, more specifically, from west to east.
An example of this process occurring is the interaction between a low-pressure system (cyclone) over India and a high-pressure system (anti-cyclone) over Australia. The two forces work together to produce heavy rainstorms over much of India and parts of Asia.
The reason why hurricanes form over the warm waters of the tropics is because they need heat energy to remain stable. Stable means not changing or moving; therefore, a hurricane that forms over a cold region will eventually decay into a depression.
Hurricanes require a lot of heat to form, which is why they tend to form over tropical oceans (at least 26 degC). Because the warm ocean warms the air above it, it rises quickly. Because water evaporates fast from the heated ocean surface, the rising air contains a large volume of water vapour. This makes the air very unstable - it can't hold as much moisture as normal air, so it must change direction often or blow away from land.
Tropical cyclones are divided into three categories based on strength: tropical depressions, tropical storms, and hurricanes. A depression is defined as a low-pressure area with sufficient atmospheric instability to produce cloudiness and wind gusts strong enough to be noticed by ship captains. It may or may not have a circulation center. A storm is similar to a depression in structure but has a well-defined center of circulation. A hurricane has an eye surrounded by intense winds. These definitions apply around the world, except in areas where terms have different meanings such as in Canada or Australia where "tropical cyclone" means a system with these characteristics located over the Indian Ocean or the Pacific Ocean, respectively.
A tropical cyclone originates when an area of low pressure develops within a tropical ocean. The process that leads up to this formation takes place hundreds or even thousands of miles away from any land mass. Once it reaches sea level, the low pressure system begins to pull water vapor into itself until it reaches its saturation point.
Tropical cyclones, which include hurricanes and typhoons, are the same weather event. Meteorologists use the term "tropical cyclone" to define a revolving, structured system of clouds and thunderstorms that originates over tropical or subtropical seas and has closed, low-level circulation. Such systems can produce heavy rainfall, strong winds, and large waves.
The terms hurricane, typhoon, and storm all mean the same thing: a violent windstorm with considerable precipitation. Although hurricanes and typhoons are often used interchangeably, they have different origins and require different preparations. A hurricane is a tropical cyclone that forms in the Atlantic Ocean or the Caribbean Sea. They are fueled by the heat of the sun and water vapor from the ocean. A typhoon is a tropical cyclone that forms in the Pacific Ocean. They are fueled by the heat of the equator and water vapor from the ocean.
A storm is defined as a rapid movement of air at the surface of the earth, accompanied by rain and high winds. This definition applies to any type of storm, including hurricanes, typhoons, and tornadoes. However only certain types of storms are called "tropical". A tropical storm is defined as a weak but significant tropical cyclone located anywhere within the tropics: between 23 degrees north and 23 degrees south latitude.
They are not just the result of hurricanes. Although hurricanes are most closely connected with storm surges, they are not the only storms capable of pushing water inland. If the winds are powerful enough, tropical depressions and tropical storms can potentially inundate coasts. Storm surges can be life-threatening during powerful winter storms. Flooding from large waves and high tides can spread disease through contaminated water, and fall trees can block roads.
A tropical depression or tropical storm cannot cause a sea level rise or a flood wave unless it makes landfall. Landfalls include being hit by at least 1 mm of rain in some part of the country; this may happen if the center of the storm is over land or if its outer bands bring rainfall to any part of the continent.
A sea level rise occurs when the water level rises along coastlines or within estuaries. A flood wave is a surface elevation increase caused by wind-driven water that reaches far away from where it comes from. This can happen when strong winds blow water toward land or into open bodies of water. Flood waves can reach far beyond the immediate vicinity of their source. For example, wind-blown waves caused by a hurricane can travel for hundreds of miles after they reach the ocean.
Flooding from storm surges can spread disease through contaminated water, and fall trees can block roads.