Definitions
A hurricane is a storm system with a closed circulation around a centre of low pressure, fueled by the heat released when moist air rises and condenses.
A hurricane is also called a tropical cyclone. This name is more scientific since it underscores the storms' origin in the tropics and their cyclonic nature. In this article we are going to use the term tropical cyclone rather than hurricane.
Basics
A tropical cyclone is a name used to describe circle-shaped weather. All tropical cyclones form over the warm ocean waters in the warm part of Earth near the equator. Most tropical cyclones create strong winds and heavy rain. While some tropical cyclones stay out in the sea, others sometimes pass over land, which can be dangerous because they can cause a lot of damage.
Terminology: A tropical cyclone is a low-pressure system (where the air pushes down less) and a cyclonic storm found in the warm part of Earth near the equator on Earth. There are several names for tropical cyclones, depending on where they happen and their strength: "tropical depressions", "tropical storms", and "hurricanes", along with other names used in different places on Earth, such as "cyclones" and "typhoons".
When winds get faster than 120 km/h or 74 mph, tropical cyclones are called "hurricanes" in the North Atlantic Ocean and Eastern and Central Pacific Ocean east of the international dateline. They are called "typhoons" or sometimes "super typhoons" if they are really strong in the Pacific Ocean west of the dateline. They are known as "cyclones" in the North Indian Ocean and in the Southern hemisphere.
Formation
A rare tropical cyclone in the south AtlanticA tropical cyclone forms in the warm parts of the earth when moist, hot air rises. It starts out as a group of storms when the water gets as hot as 80 degrees or hotter. It then begins to slowly improve and look like a spiral shape. When convection bursts happen and a low-level circulation reaches the surface, it's then called a tropical disturbance.
If winds reach 25 mph or more, it is then called a "tropical depression". When tropical depression strengthens with winds staying at speeds of 39 mph, it is then called a "tropical storm". Tropical storms can turn into hurricanes (or typhoons and cyclones) when winds reach 74 mph. Tropical cyclones can form in the Atlantic Ocean, the Pacific Ocean, the Indian Ocean, and in the southern parts of the Earth.
The Coriolis effect causes winds to spiral. Because of this, tropical cyclones form close to the equator only in special conditions. Areas with cold seas, fast winds high up in the air, and/or dry air do not have the right conditions for tropical cyclones to form.
Locations and times
Tropical cyclones form in the northern Atlantic, northern Pacific, southwestern Pacific, and Indian Ocean. Tropical cyclones may rarely form elsewhere in the world.
The Atlantic Ocean has around ten hurricanes each year. They can hit Central America, Mexico, the United States, Canada, Bermuda Island, and the Caribbean Islands. Most hurricanes form between June and November. Tropical cyclones rarely form in the south Atlantic.
The northeastern Pacific has around 16 cyclones a year. Most do not hit land. On average, two cyclones hit Mexico each year. They rarely affect Central America, California, or Hawaii. Most form between May and November.
The northwestern Pacific has around 27 tropical cyclones a year. They can hit Japan, China, North and South Korea, Taiwan, the Philippines, and some Pacific islands. This area has typhoons year-round.
The northern Indian Ocean has around six cyclones each year. They hit India, Bangladesh, Pakistan, and nearby countries. Cyclones form year-round in this area.
The southern Indian Ocean has around twenty-one cyclones each year. They can hit Australia, Indonesia, Madagascar, and southern Africa. Most cyclones form between October and May.
The southwest Pacific has around ten cyclones per year. They can hit some Pacific Islands, Australia, and New Zealand. Most cyclones form between October and May.
Breaking up: Tropical cyclones can break up and disappear for several reasons. If they move over land, they no longer get moisture from the ocean waters. But sometimes, tropical cyclones can move over colder waters and begin to become an extra-tropical cyclone. Sometimes, they may be swallowed up by a larger system (like another stronger tropical cyclone, or another extra-tropical system). They may run into wind shear, which destroys convection and tears apart the system. Studies in the 2000s have shown that a lot of dust could also weaken a hurricane.
Naming
Tropical cyclones are usually given names because it helps in forecasting, tracking, and reporting. They are named once they have steady winds of 62 km/h. Committees of the World Meteorological Organization pick names. Once named, a cyclone is usually not renamed.
The Atlantic uses a list of twenty-one names, starting with all letters of the alphabet except Q, V, X, Y, and Z. Names switch between male and female, and are taken from the English, Spanish and French languages. The lists repeat every six years. Destructive or deadly hurricanes have their names "retired". When a name is retired, it is removed from the list and replaced by a new name of the same gender.[1]
Beginning in 2002, the naming system for tropical cyclones have also been shared with subtropical cyclones after the National Hurricane Center decided to name both type of cyclonic storm under the same category.
The eastern Pacific used a similar system of lists, but also with names starting in X, Y, and Z. In both the Atlantic and Pacific, if more cyclones form then there are names, the Greek alphabet is used to name more cyclones. The central Pacific uses four lists of Hawaiian names. They are used in order without regard to the year.
The western Pacific uses five lists of twenty-eight names. Each country on the committee offers two names. The names are used in order of the countries' English names without regard to year. Names are also retired from these lists.
The areas around Australia use three separate sets. The south Pacific near Fiji uses another set. All are used without regard to year. Names can also be retired.
The southwestern Indian Ocean uses a list of twenty-six names. A new list is used each year. If the number of cyclones is higher than the number of names, more cyclones are not named.
Impact
Damage from a tropical cycloneWhen tropical cyclones make landfall, they create some damage as a result. But sometimes, when a strong tropical cyclone makes landfall, it creates high winds, heavy rain, storm surge, and in some cases, even tornadoes. Tropical cyclones are also known to kill people and destroy cities. In the last 200 years, about 1.5 million people have been killed by tropical cyclones.
Some long-term effects from tropical cyclones that can cause problems to a country, such as millions or even billions of dollars in damages can make relief supports difficult. Depending where a tropical cyclone hits, they usually create far more destruction when a tropical cyclone hits big city compared to making landfall in the countryside.
Wind damages can account up to 83% of the total damages caused when broken wreckage pieces from destroyed objects can become deadly flying pieces.[2] Other issues such as flooding can occur when rainfalls and/or storm surges pour water onto land.[3] Storm surges are also statistically known to be the cause of 90% of tropical cyclone-related deaths.
Other problems such as indirect deaths can also occur after a tropical cyclone makes landfall. For example, New Orleans, Louisiana suffered from poor sanitary conditions after Hurricane Katrina hit in 2005, as contaminated flood waters created disease and relief efforts were held up.[4]
Classifications
Tropical cyclones are classified into different categories depending on their strength and location. The National Hurricane Center which observes hurricanes in the Atlantic Ocean and Eastern and cCntral Pacific Ocean classify them into the Saffir-Simpson Hurricane Scale.
Tropical cylones in other places such as the Western Pacific Ocean or the Southern Hemisphere are classified on similar scales. For example; if a tropical storm in the western Pacific reaches hurricane-strength winds, it is then officially recognized as a typhoon.
A tropical depression is an organized group of clouds and thunderstorms with a clear surface circulation and maximum sustained winds of less than 17 m/s (33 kt, 38 mph, or 62 km/h). It has no eye and does not usually have the spiral shape of more powerful storms. Only the Philippines are known to name tropical depressions.
A tropical storm is an organized system of strong thunderstorms with a very clear surface circulation and maximum sustained winds between 17 and 32 m/s (34–63 kt, 39–73 mph, or 62–117 km/h). At this point, the cyclonic shape starts to form, although an eye does not usually appear in tropical storms. Most tropical cyclone agencies beginning naming cyclonic storms at this point, except for the Philippines which have their own way of naming cyclones.
A hurricane or typhoon is a cyclonic weather system with sustained winds of at least 33 m/s (64 kt, 74 mph, or 118 km/h). A tropical cyclone of this strength usually develop an eye, an area of calm conditions at the center of circulation. The eye is often seen from space as a small, round, cloud-free spot. Surrounding the eye is the eyewall, an area in which the strongest thunderstorms and winds spin around the storm's center. The fastest sustained windspeed founded in tropical cyclones is thought to be 85 m/s (165 kt, 190 mph, 305 km/h).
Many people from different nations and regions around the world call tropical cyclones in other different ways depending on their location. In the North Atlantic Ocean and East & Central Pacific, tropical cyclones are called "hurricanes"; while in the West Pacific, tropical cyclones are also known as "typhoons". But only the North Indian basin and the entire Southern Hemisphere call these storms "tropical cyclones".
Saffir-Simpson Hurricane Scale
| Saffir-Simpson Hurricane Scale |
| Category |
Wind speed |
Storm surge |
|
mph
(km/h) |
ft
(m) |
| 5 |
≥156
(≥250) |
>18 (>5.5) |
| 4 |
131–155
(210–249) |
13–18
(4.0–5.5) |
| 3 |
111–130
(178–209) |
9–12
(2.7–3.7) |
| 2 |
96–110
(154–177) |
6–8
(1.8–2.4) |
| 1 |
74–95
(119–153) |
4–5
(1.2–1.5) |
| Additional classifications |
Tropical
storm |
39–73
(63–117) |
0–3
(0–0.9) |
Tropical
depression |
0–38
(0–62) |
0
(0) |
TheSaffir-Simpson Hurricane Scale is a scale categorizing mainly Western Hemisphere tropical cyclones that go beyond the strength of "tropical depressions" and "tropical storms", and thus become hurricanes. The categories into which the scale separates hurricanes are noted by the strength of their maximum sustained wind speeds. The classifications are used mainly for use in measuring the possible damage and flooding a hurricane will create when it makes landfall.
Very recently, the scale was also used to classify subtropical cyclones after a change in the rules made by the National Hurricane Center in 2002.
The Saffir-Simpson Hurricane Scale is used only to describe hurricanes that form in the Atlantic Ocean and northern Pacific Ocean, to the east of the International Date Line. Other areas call their tropical storms "cyclones" and "typhoons", and use their own classification scales.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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