User:DavidH/stormbox

Tropical storm

A tropical storm is a tropical cyclone that is less intense than a hurricane, with maximum winds of 39 to 73 miles per hour (34–63 knots). In official weather forecasts and public warnings in the North Atlantic region, the term tropical storm is one of three (including tropical depression and hurricane) used to describe the level of development and the maximum sustained winds of tropical cyclones.

Though tropical storms are weaker than hurricanes in general, they can bring damaging winds, thunderstorms, and heavy rain to coastal areas at landfall. Depending on terrain, movement of the system, and other conditions, a tropical storm's effects can be devastating, especially when prolonged rainfall causes flash floods and mudslides. The deadliest tropical storms have killed hundreds of people, while a few have killed thousands.

Terminology

In other regions, different official terms are used for tropical cyclones (see regional storm terminology). Also, it is common for news media and the public to use tropical storm as a general term for tropical weather systems.

When it designates a tropical storm, the National Hurricane Center assigns a first name that applies as long as the system is classified as a tropical storm or a hurricane, so tropical storms and hurricanes are also referred to as named storms.

Even in the official sense, tropical storm is used to refer to conditions (winds of tropical storm-level intensity) that may be caused by a system with a different official designation. Therefore, a tropical storm warning is issued for a coastal area as a hurricane approaches if winds of less than hurricane force are expected. For information on official definitions, see the National Hurricane center definitions page.

Tropical storms are below the level of strength that is categorized by the Saffir-Simpson hurricane scale. No official categorization is applied to intensities of tropical storms.

Rate of occurrence

As with all tropical cyclones, tropical storms are most likely to occur in particular regions of the globe at different times of the year.

In 2005 in the North Atlantic, 27 tropical storms occurred, a new record for the maximum number of tropical storms in one season. Of the 27 storms, 15 became hurricanes and seven became major hurricanes.

By contrast, in 1980 for example, there were 11 named storms, of which 9 became hurricanes and 2 became major hurricanes.

While the time of greatest tropical cyclone activity ("hurricane season") extends officially for six months in North America, early-season and late-season storms form under conditions that are less favorable for development of very strong tropical cyclones. Therefore, tropical storms are less likely to develop into hurricanes, especially strong hurricanes, at the beginning and end of the season.

Characteristics

Tropical storms arise from disturbed weather in the tropics. Generally, the precursor to a tropical storm is a tropical wave which develops into a tropical depression and then a tropical storm, as thunderstorms organize around a low-pressure center and maximum sustained winds reach 17 to 33 m/s (34–63 knots, 39–73 mph, or 62–117 km/h)—above tropical depression and below hurricane intensity.

A system can be designated a tropical storm before reaching hurricane strength or after diminishing from it. The designation of a particular system may change several times, as dictated by the maximum winds, during its life.

At tropical storm strength, a system starts to develop a distinctive cyclonic shape, though usually without the clear "eye" that is evident in hurricanes.

When a tropical storm develops further, an area of relative calm and lowest atmospheric pressure forms, creating an eye, or circular area without clouds at the system's center. The eye is usually visible in satellite images. Surrounding the eye is the eyewall, an area about 10–50 mi (16–80 km) wide in which the strongest thunderstorms and winds circulate around the storm's center. The circulation is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Tropical Depression 19, which formed during the 2005 Atlantic hurricane season, showing the lack of organization in tropical depressions when compared to stronger cyclones.

Related weather systems

Tropical depression

A tropical depression is an organized system of clouds and thunderstorms with a defined surface circulation and maximum sustained winds of less than 17 m/s (33 kt, 38 mph, or 62 km/h). A depression has no eye and typically has not organized into the distinctive spiral shape of more powerful storms. A depression is already becoming a tropical low-pressure system, however, hence the name "depression".

See also

Meteorology

• Cyclone
• Hot tower
• Eyewall
• Subtropical cyclone
• Anticyclone

Forecasting and preparation

• Catastrophe modeling
• Saffir-Simpson Hurricane Scale
• Hurricane proof building
• Hurricane preparedness

Categories

• Category:Lists of tropical cyclones
• Category:Tropical cyclones by basin
• Category:Tropical cyclones by season
• Category:Tropical cyclones by strength
• Category:Tropical cyclones by region

External links

Tracking and Warning

• Joint Typhoon warning Center - Western Pacific
• MetService, New Zealand - Tasman Sea, South Pacific south of 25&deg S
• Australian Bureau of Meteorology - Southern hemisphere from 90° E to 160° E
• Canadian Hurricane Centre - Northwest Atlantic (overlaps US NHC)
• Hurricane & Storm Tracking for the Atlantic & Pacific Oceans - Shows all current hurricanes and their tracks