Rapid intensification

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Infrared satellite loop of Typhoon Maria as it underwent rapid intensification Maria RBTOP 2018-07-05 1330Z-2030Z.gif
Infrared satellite loop of Typhoon Maria as it underwent rapid intensification

Rapid intensification is a meteorological condition that occurs when a tropical cyclone intensifies dramatically in a short period of time. The United States National Hurricane Center defines rapid intensification as an increase in the maximum sustained winds of a tropical cyclone of at least 30 knots (35 mph; 55 km/h) in a 24-hour period. [1]

Meteorology Interdisciplinary scientific study of the atmosphere focusing on weather forecasting

Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw modest progress in the field after weather observation networks were formed across broad regions. Prior attempts at prediction of weather depended on historical data. It was not until after the elucidation of the laws of physics and more particularly, the development of the computer, allowing for the automated solution of a great many equations that model the weather, in the latter half of the 20th century that significant breakthroughs in weather forecasting were achieved. An important domain of weather forecasting is marine weather forecasting as it relates to maritime and coastal safety, in which weather effects also include atmospheric interactions with large bodies of water.

Tropical cyclone Is a rotating storm system

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. Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone. A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean; in the south Pacific or Indian Ocean, comparable storms are referred to simply as "tropical cyclones" or "severe cyclonic storms".

National Hurricane Center division of the United States National Weather Service

The National Hurricane Center (NHC) is the division of the United States' National Weather Service responsible for tracking and predicting tropical weather systems between the Prime Meridian and the 140th meridian west poleward to the 30th parallel north in the northeast Pacific Ocean and the 31st parallel north in the northern Atlantic Ocean. The agency, which is co-located with the Miami branch of the National Weather Service, is situated on the campus of Florida International University in University Park, Florida.


Necessary conditions


In order for rapid intensification to occur, several conditions must be in place. Water temperatures must be extremely warm (near or above 30 °C, 86 °F), and water of this temperature must be sufficiently deep such that waves do not churn deeper cooler waters up to the surface. Wind shear must be low; when wind shear is high, the convection and circulation in the cyclone will be disrupted [2] . Dry air can also limit the strengthening of tropical cyclones. [3]

Sea surface temperature Water temperature close to the oceans surface

Sea surface temperature (SST) is the water temperature close to the ocean's surface. The exact meaning of surface varies according to the measurement method used, but it is between 1 millimetre (0.04 in) and 20 metres (70 ft) below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a short distance of the shore. Localized areas of heavy snow can form in bands downwind of warm water bodies within an otherwise cold air mass. Warm sea surface temperatures are known to be a cause of tropical cyclogenesis over the Earth's oceans. Tropical cyclones can also cause a cool wake, due to turbulent mixing of the upper 30 metres (100 ft) of the ocean. SST changes diurnally, like the air above it, but to a lesser degree. There is less SST variation on breezy days than on calm days. In addition, ocean currents such as the Atlantic Multidecadal Oscillation (AMO), can effect SST's on multi-decadal time scales, a major impact results from the global thermohaline circulation, which affects average SST significantly throughout most of the world's oceans.

Wind shear

Wind shear, sometimes referred to as wind gradient, is a difference in wind speed or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizontal wind shear. Vertical wind shear is a change in wind speed or direction with change in altitude. Horizontal wind shear is a change in wind speed with change in lateral position for a given altitude.


Usually, an anticyclone in the upper layers of the troposphere above the storm must be present as well—for extremely low surface pressures to develop, air must be rising very rapidly in the eyewall of the storm, and an upper-level anticyclone helps channel this air away from the cyclone efficiently. [4] [ further explanation needed ] Hot towers have been implicated in tropical cyclone rapid intensification, though diagnostically has seen varied skill across basins. [5]

Anticyclone opposite to a cyclone

An anticyclone is a weather phenomenon defined by the United States National Weather Service's glossary as "a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere". Effects of surface-based anticyclones include clearing skies as well as cooler, drier air. Fog can also form overnight within a region of higher pressure. Mid-tropospheric systems, such as the subtropical ridge, deflect tropical cyclones around their periphery and cause a temperature inversion inhibiting free convection near their center, building up surface-based haze under their base. Anticyclones aloft can form within warm core lows such as tropical cyclones, due to descending cool air from the backside of upper troughs such as polar highs, or from large scale sinking such as the subtropical ridge. The evolution of an anticyclone depends on a few variables such as its size, intensity, moist-convection, Coriolis force etc.

Troposphere The lowest layer of the atmosphere

The troposphere is the lowest layer of Earth's atmosphere, and is also where nearly all weather conditions take place. It contains approximately 75% of the atmosphere's mass and 99% of the total mass of water vapor and aerosols. The average height of the troposphere is 18 km in the tropics, 17 km in the middle latitudes, and 6 km in the polar regions in winter. The total average height of the troposphere is 13 km.

Eye (cyclone) region of mostly calm weather at the center of strong tropical cyclones

The eye is a region of mostly calm weather at the center of strong tropical cyclones. The eye of a storm is a roughly circular area, typically 30–65 km (20–40 miles) in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather and highest winds occur. The cyclone's lowest barometric pressure occurs in the eye and can be as much as 15 percent lower than the pressure outside the storm.

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 42 millibars (1.240 inHg) over a 24-hour period. [6] However it is now defined as an increase in the maximum sustained winds of a tropical cyclone of at least 30 knots (35 mph; 55 km/h) in a 24-hour period. [1]

See also

Explosive cyclogenesis rapidly deepening extratropical cyclonic low-pressure area

Explosive cyclogenesis is the rapid deepening of an extratropical cyclonic low-pressure area. The change in pressure needed to classify something as explosive cyclogenesis is latitude dependent. For example, at 60° latitude, explosive cyclogenesis occurs if the central pressure decreases by 24 mbar (hPa) or more in 24 hours. This is a predominantly maritime, winter event, but also occurs in continental settings, even in the summer. This process is the extratropical equivalent of the tropical rapid deepening. Although their cyclogenesis is totally different from that of tropical cyclones, bombs can produce winds of 74–95 mph, the same order as the first categories of the Saffir-Simpson scale and give heavy precipitation. Even though only a minority of the bombs become so strong, some have caused significant damage.

Annular tropical cyclone

An annular tropical cyclone is a tropical cyclone that features a normal to large, symmetric eye surrounded by a thick and uniform ring of intense convection, often having a relative lack of discrete rainbands, and bearing a symmetric appearance in general. As a result, the appearance of an annular tropical cyclone can be referred to as akin to a tire or doughnut. Annular characteristics can be attained as tropical cyclones intensify; however, outside the processes that drive the transition from asymmetric systems to annular systems and the abnormal resistance to negative environmental factors found in storms with annular features, annular tropical cyclones behave similarly to asymmetric storms. Most research related to annular tropical cyclones is limited to satellite imagery and aircraft reconnaissance as the conditions thought to give rise to annular characteristics normally occur over water well removed from landmasses where surface observations are possible.

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