Tropical cyclone in the context of "Natural disaster"

A natural phenomenon is an observable event which is not man-made. Examples include: sunrise, weather, fog, thunder, tornadoes; biological processes, decomposition, germination; physical processes, wave propagation, erosion; tidal flow, and natural disasters such as electromagnetic pulses, volcanic eruptions, hurricanes and earthquakes.

Extreme weather includes unexpected, unusual, severe, or unseasonal weather; weather at the extremes of the historical distribution—the range that has been seen in the past. Extreme events are based on a location's recorded weather history. The main types of extreme weather include heat waves, cold waves, droughts, and heavy precipitation or storm events, such as tropical cyclones. Extreme weather can have various effects, from natural hazards such as floods and landslides to social costs on human health and the economy. Severe weather is a particular type of extreme weather which poses risks to life and property.

Weather patterns in a given region vary with time, and so extreme weather can be attributed, at least in part, to the natural climate variability that exists on Earth. For example, the El Niño-Southern Oscillation (ENSO) or the North Atlantic oscillation (NAO) are climate phenomena that impact weather patterns worldwide. Generally speaking, one event in extreme weather cannot be attributed to any one single cause. However, certain system wide changes to global weather systems can lead to increased frequency or intensity of extreme weather events.

In fluid dynamics, a vortex (pl.: vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids and may be observed in smoke rings, whirlpools in the wake of a boat, and in the winds surrounding a tropical cyclone, tornado, or dust devil.

Vortices are a major component of turbulent flow. The distribution of velocity, vorticity (the curl of the flow velocity), as well as the concept of circulation are used to characterize vortices. In most vortices, the fluid flow velocity is greatest next to its axis and decreases in inverse proportion to the distance from the axis.

The 1970 Bhola cyclone (also known as the Great Cyclone of 1970 or simply the Bhola Cyclone) was the deadliest tropical cyclone on record, as well as one of the deadliest humanitarian disasters ever recorded. It struck East Pakistan (present-day Bangladesh) and India's West Bengal on 12 November 1970. At least 300,000 people died in the storm, possibly as many as 500,000, primarily as a result of the storm surge that flooded much of the low-lying islands of the Ganges Delta. The Bhola cyclone was the sixth and strongest cyclonic storm of the 1970 North Indian Ocean cyclone season.

The cyclone formed over the central Bay of Bengal on 8 November and traveled northward, intensifying as it did so. It reached its peak with winds of 185 km/h (115 mph) on 10 November, and made landfall on the coast of East Pakistan on the following afternoon. The storm surge devastated many of the offshore islands, wiping out villages and destroying crops throughout the region. In the most severely affected upazila Tazumuddin, over 45% of the population of 167,000 were killed by the storm.

Hurricane Harvey was a powerful and devastating tropical cyclone that made landfall in Texas and Louisiana in August 2017, causing catastrophic flooding and more than 100 deaths. It is tied with 2005's Hurricane Katrina as the costliest tropical cyclone on record, inflicting $125 billion (2017 USD) in damage, primarily from catastrophic rainfall-triggered flooding in Greater Houston and Southeast Texas; this made the storm the costliest natural disaster recorded in Texas at the time. It was the first major hurricane to make landfall in the United States since Wilma in 2005, ending a record 12-year span in which no hurricanes made landfall at the intensity of a major hurricane throughout the country. In a four-day period, many areas received more than 40 inches (1,000 mm) of rain as the system slowly meandered over eastern Texas and adjacent waters, causing unprecedented flooding. With peak accumulations of 60.58 in (1,539 mm) in Nederland, Texas, Harvey was the wettest tropical cyclone on record in the United States. The resulting floods inundated hundreds of thousands of homes, which displaced more than 30,000 people and prompted more than 17,000 rescues.

The eighth named storm, third hurricane, and first major hurricane of the extremely active 2017 Atlantic hurricane season, Harvey developed from a tropical wave to the east of the Lesser Antilles, reaching tropical storm status on August 17. The storm crossed through the Windward Islands on the following day, making landfall on the southern end of Barbados and a second landfall on Saint Vincent. Upon entering the Caribbean, Harvey began to weaken due to moderate wind shear, and degenerated into a tropical wave north of Colombia, late on August 19. The remnants were monitored for regeneration as it continued west-northwestward across the Caribbean and the Yucatán Peninsula, before redeveloping over the Bay of Campeche on August 23. Harvey then began to rapidly intensify on August 24, regaining tropical storm status and becoming a hurricane later that day.

Climate change affects tropical cyclones in a variety of ways: an intensification of rainfall and wind speed, an increase in the frequency of very intense storms and a poleward extension of where the cyclones reach maximum intensity are among the consequences of human-induced climate change. Tropical cyclones use warm, moist air as their source of energy or fuel. As climate change is warming ocean temperatures, there is potentially more of this fuel available.

Between 1979 and 2017, there was a global increase in the proportion of tropical cyclones of Category 3 and higher on the Saffir–Simpson scale. The trend was most clear in the north Indian Ocean, North Atlantic and in the Southern Indian Ocean. In the north Indian Ocean, particularly the Arabian Sea, the frequency, duration, and intensity of cyclones have increased significantly. There has been a 52% increase in the number of cyclones in the Arabian Sea, while the number of very severe cyclones have increased by 150%, during 1982–2019. Meanwhile, the total duration of cyclones in the Arabian Sea has increased by 80% while that of very severe cyclones has increased by 260%. In the North Pacific, tropical cyclones have been moving poleward into colder waters and there was no increase in intensity over this period. With 2 °C (3.6 °F) warming, a greater percentage (+13%) of tropical cyclones are expected to reach Category 4 and 5 strength. A 2019 study indicates that climate change has been driving the observed trend of rapid intensification of tropical cyclones in the Atlantic basin. Rapidly intensifying cyclones are hard to forecast and therefore pose additional risk to coastal communities.