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Tropical weather systems comprise a number of features ranging from the Inter-tropical Convergence Zone (ITCZ) to hurricanes. Most reporters tend to focus on hurricanes because they are big and ferocious however tropical waves, tropical depressions, or even the ITCZ cause significant damage. In 1998 a slow moving tropical depression dumped almost three feet of rain on Central America triggering massive landslides which killed almost 20,000 people. Heavy rains from a tropical disturbance in May 2004 also triggered mudslides in Haiti and the Dominican Republic killing over 2,000 people and wiping out several villages and later that year, rain associated with Tropical Storm Jeanne caused more destruction and death.


Types of tropical weather systems affecting the Caribbean

  • Inter-Tropical Convergence Zone (ITCZ)
  • Trough
  • Tropical Cyclone (Tropical Depression, Tropical Storm, and Hurricane)
  • Tropical Wave
  • Tropical Disturbance
The Inter-tropical Convergence Zone is a region spanning from five degrees south to five degrees north of the equator where northeasterly and southeasterly tradewinds converge, forming an often continuous band of clouds or thunderstorms near the equator. The ITCZ, is a key component of the global circulation system, and can move up to 40 to 45 degrees north and south of the equator. The thunderstorms and large-scale spin in the ITCZ is an essential element to the birth of tropical cyclones which is deal with in greater detail below. As the ITCZ move north, it can bring torrential showers and flooding to CDERA member states. The severe flooding experienced by Guyana in January 2005 was a result of the ITCZ interacting with a surface trough.
Tropical Cyclone
A warm-core low pressure system which develops over tropical, and sometimes subtropical, waters, and has an organized circulation. Depending on sustained surface winds, the system (in the Atlantic and Eastern Pacific Oceans) is classified as a tropical disturbance, a tropical depression, a tropical storm, or a hurricane. In the Caribbean, the layman tend to lump them all together and call them “hurricanes” however the correct term is a “cyclone”. In the Indian Ocean they are referred to Cyclones, in the Western Pacific as Typhoons, and near Australia as Willy Willy. The individual types of cyclones which affect the Caribbean are detailed below.
Tropical Wave

All things being equal, tropical cyclones will form from a tropical wave. The term which scientists use to describe all the right conditions that form a cyclone is called Cyclogenesis (the genesis or beginning of a cyclone).

A Tropical Wave is an elongated area of low pressure, originating over Africa and blown across the Atlantic by the tradewinds towards the Caribbean Sea, crossing Central America and into the Pacific Ocean. These "waves" can be more correctly thought of as the convectively active troughs along an extended wave train. About 60 of these are generated each year during starting around April or May and continuing to October or November, coinciding with the Atlantic Hurricane Season (June-November). While only about 60% of the Atlantic tropical storms and minor hurricanes (Saffir-Simpson Scale categories 1 and 2) originate from easterly waves, nearly 85% of the intense (or major) hurricanes have their origins as easterly waves. It is suggested, though, that nearly all of the tropical cyclones that occur in the Eastern Pacific Ocean can also be traced back to Africa.

Tropical Disturbance
A discrete tropical weather system of apparently organized mass of thunderstorm, with a slight cyclonic circulation. It is generally 200 to 600 kilometers (100 to 300 nautical miles) in diameter originating in the tropics or subtropics and maintaining this character for 24 hours or more. Disturbances progressing
Tropical Depression
A tropical cyclone in which the maximum sustained wind speed is between 37 and 61 kph (23-38 mph).
Tropical Storm
Once a tropical depression has intensified to the point where its maximum sustained winds are between 61-118 kph (39-73 mph), it becomes a tropical storm. It is at this time that it is assigned a name. During this time, the storm itself becomes more organized and begins to become more circular in shape -- resembling a hurricane. Rainfall in tropical storms is usually more concentrated near the center with outer rainfall organizing into distinct bands.
As surface pressures continue to drop, a tropical storm becomes a hurricane when sustained wind speeds reach 119 kph (74 mph). A pronounced rotation develops around the central core and the system develops an "eye”. Located just outside of the eye is the eye wall. This is the location within a hurricane where the most damaging winds and intense rainfall is found. Inside the eye, the weather is calm. There are five categories of hurricanes classified on the Saffir/Simpson Scale (see below). The last three are regarded as “intense” or “major” hurricanes.
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