meteorology Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...

, rapid intensification is a situation where a

tropical cyclone A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Dep ...

intensifies dramatically in a short period of time. The United States

National Hurricane Center The National Hurricane Center (NHC) is the division of the United States' NOAA/National Weather Service responsible for tracking and predicting tropical weather systems between the Prime Meridian and the 140th meridian west poleward to the 3 ...

defines rapid intensification as an increase in the

maximum sustained winds The maximum sustained wind associated with a tropical cyclone is a common indicator of the intensity of the storm. Within a mature tropical cyclone, it is found within the eyewall at a distance defined as the radius of maximum wind, or RMW. U ...

of a tropical cyclone of at least in a 24-hour period.

Necessary conditions

External

In order for rapid intensification to occur, several conditions must be in place. Water temperatures must be extremely warm (near or above ), and water of this temperature must be sufficiently deep such that waves do not churn deeper cooler waters up to the surface.

Wind shear Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizont ...

must be low; when wind shear is high, the

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...

and circulation in the cyclone will be disrupted. Dry air can also limit the strengthening of tropical cyclones.

Internal

Usually, an

anticyclone An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from ...

in the upper layers of the

troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. Fro ...

above the storm must also be present for extremely low surface pressures to develop. This is because air must be converging towards the low pressure at the surface, which then forces the air to rise very rapidly in the eyewall of the storm. Due to conservation of mass, this requires a divergence of wind at the top of the troposphere. This process is aided by an upper-level anticyclone which helps efficiently channel this air away from the cyclone. Hot towers have been implicated in tropical cyclone rapid intensification, though they have diagnostically seen varied impacts across basins.

Previous nomenclature and definitions

The United States National Hurricane Center previously defined ''rapid deepening'' of a tropical cyclone, when the minimum central pressure decreased by over a 24-hour period. Currently it is defined as an increase in the maximum sustained winds of a tropical cyclone of at least in a 24-hour period. However, recent research suggests that mean sea level pressure is a better predictor of damage from hurricanes making landfall in the continental United States.

Forecasting

The later half of the 21st century forecasts envision stronger greenhouse gas forcing dominating natural variability which along with warming sea surface temperatures will create more intense hurricanes along the U.S. Atlantic coasts. The same period forecasts for the Gulf of Mexico coasts indicate sufficient

wind shear Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizont ...

in place to somewhat diminish rapid storm intensification. Atlantic storms,

Hurricane Maria Hurricane Maria was a deadly Category 5 hurricane that devastated the northeastern Caribbean in September 2017, particularly Dominica, Saint Croix, and Puerto Rico. It is regarded as the worst natural disaster in recorded history to affect ...

and

Hurricane Harvey Hurricane Harvey was a devastating Category 4 hurricane that made landfall on 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 ...

intensified rapidly in 2017.

References