Tropical cyclone

Hurricane Isabel in 2003 as seen from the International Space Station. The eye, eyewall, and surrounding rainbands, characteristics of tropical cyclones in the narrow sense, are clearly visible in this view from space.
Diagram of a tropical cyclone in the Northern hemisphere
Hurricane Paulette, in 2020, is an example of a sheared tropical cyclone, with deep convection slightly removed from the center of the system.
Thunderstorm activity in the eyewall of Cyclone Bansi as seen from the International Space Station, on January 12, 2015
Storm track of Typhoon Ioke, showing recurvature off the Japanese coast in 2006
Three tropical cyclones of the 2006 Pacific typhoon season at different stages of development. The weakest (left) demonstrates only the most basic circular shape. A stronger storm (top right) demonstrates spiral banding and increased centralization, while the strongest (lower right) has developed an eye.
Relief efforts for Hurricane Dorian in the Bahamas
Sunset view of Hurricane Isidore's rainbands photographed at 7000 ft
"Hurricane Hunter" – WP-3D Orion is used to go into the eye of a hurricane for data collection and measurements purposes.
A general decrease in error trends in tropical cyclone path prediction is evident since the 1970s

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/or squalls.

- Tropical cyclone

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Sudden, sharp increase in wind speed lasting minutes, as opposed to a wind gust, which lasts for only seconds.

Rainbow after a squall
A shelf cloud such as this one can be a sign that a squall is imminent
A summer squall line in Southern Ontario, producing lightning and distant heavy rains.
A wake low is a mesolow

Squalls are sometimes associated with hurricanes or other cyclones, but they can also occur independently.

Beaufort scale

Empirical measure that relates wind speed to observed conditions at sea or on land.

A ship in Force 12 storm at sea
Sir Francis Beaufort

However, forces 13 to 17 were intended to apply only to special cases, such as tropical cyclones.

Angular momentum

Rotational analog of linear momentum.

This gyroscope remains upright while spinning due to the conservation of its angular momentum.
Velocity of the particle m with respect to the origin O can be resolved into components parallel to (v∥) and perpendicular to (v⊥) the radius vector r. The angular momentum of m is proportional to the perpendicular component v⊥ of the velocity, or equivalently, to the perpendicular distance r⊥ from the origin.
Relationship between force (F), torque (τ), momentum (p), and angular momentum (L) vectors in a rotating system. r is the position vector.
A figure skater in a spin uses conservation of angular momentum – decreasing her moment of inertia by drawing in her arms and legs increases her rotational speed.
The torque caused by the two opposing forces Fg and −Fg causes a change in the angular momentum L in the direction of that torque (since torque is the time derivative of angular momentum). This causes the top to precess.
The angular momentum of the particles i is the sum of the cross products R × MV + Σri × mivi.
The 3-angular momentum as a bivector (plane element) and axial vector, of a particle of mass m with instantaneous 3-position x and 3-momentum p.
Newton's derivation of the area law using geometric means.

Conservation of angular momentum is also why hurricanes form spirals and neutron stars have high rotational rates.

Extratropical cyclone

Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth.

A powerful extratropical cyclone over the North Atlantic Ocean in March 2022
Approximate areas of extratropical cyclone formation worldwide
An upper-level jet streak. DIV areas are regions of divergence aloft, which will lead to surface convergence and aid cyclogenesis.
Hurricane Cristobal (2014) in the north Atlantic after completing its transition to an extratropical cyclone from a hurricane
QuikSCAT image of typical extratropical cyclones over the ocean. Note the maximum winds are on the outside of the occlusion.
Extratropical cyclones spin clockwise in the Southern Hemisphere, just like tropical cyclones.
A hurricane-force extratropical cyclone in January 2016 with a distinct eye-like feature, caused by a warm seclusion
A zonal flow regime. Note the dominant west-to-east flow as shown in the 500 hPa height pattern.
A February 24, 2007 radar image of a large extratropical cyclonic storm system at its peak over the central United States.
Preferred region of snowfall in an extratropical cyclone
Cyclone Oratia showing the comma shape typical of extratropical cyclones, over Europe in October 2000.

In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, about the center of the cyclone.


Electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder.

A typical thunderstorm over a field.
Stages of a thunderstorm's life.
A cumulus congestus' transformation into a mature cumulonimbus incus.
Anvil-shaped thundercloud in the mature stage
A thunderstorm in an environment with no winds to shear the storm or blow the anvil in any one direction
Flanking line in front of a dissipating cumulonimbus incus cloud
Conditions favorable for thunderstorm types and complexes
A single-cell thunderstorm over Wagga Wagga.
A group of thunderstorms over Brazil photographed by the Space Shuttle Challenger.
A supercell thunderstorm over Chaparral, New Mexico.
The setting sun illuminates the top of a classic anvil-shaped thunderstorm cloud in eastern Nebraska, United States.
MCC moving through New England: 2 August, 2006 0600 UTC
Thunderstorm line viewed in reflectivity (dBZ) on a plan position indicator radar display
A return stroke, cloud-to-ground lightning strike during a thunderstorm.
Hailstorm in Bogotá, Colombia.
In June 2007, the town of Elie, Manitoba was struck by an F5 tornado.
Formation of numerous waterspouts in the Great Lakes region. (North America)
A flash flood caused by a severe thunderstorm
Trees uprooted or displaced by the force of a downburst wind in northwest Monroe County, Wisconsin.
How thunderstorms launch particle beams into space
Summer storm in 19th century Polish countryside - picture by Jozef Chelmonski, 1896, 107 cm (42.1 in)x163 cm (64.1 in), National Museum in Cracow

Mesoscale convective systems formed by favorable vertical wind shear within the tropics and subtropics can be responsible for the development of hurricanes.

Wind shear

Difference in wind speed and/or direction over a relatively short distance in the atmosphere.

Cirrus uncinus ice crystal plumes showing high-level wind shear, with changes in wind speed and direction
Down draft winds with associated virga allow these clouds in the eastern sky at civil twilight to mimic aurora borealis in the Mojave desert.
Microburst schematic from NASA. The direction of travel is downward until the air current hits ground level, at which point it spreads outward in all directions. The wind regime in a microburst is completely opposite to a tornado.
Strong wind shear in the high troposphere forms the anvil-shaped top of this mature cumulonimbus cloud, or thunderstorm.
Depiction of where the planetary boundary layer lies on a sunny day
Glider ground launch affected by wind shear
Effect of wind shear on aircraft trajectory. Note how merely correcting for the initial gust front can have dire consequences.
Wreckage of Delta Air Lines Flight 191 tail section after a microburst slammed the aircraft into the ground. Another aircraft can be seen flying in the background past the crash scene.
Hodograph plot of wind vectors at various heights in the troposphere. Meteorologists can use this plot to evaluate vertical wind shear in weather forecasting. (Source: NOAA)

Strong vertical wind shear within the troposphere also inhibits tropical cyclone development but helps to organize individual thunderstorms into longer life cycles which can then produce severe weather.

Northern Hemisphere

Half of Earth that is north of the Equator.

Northern Hemisphere shaded blue. The hemispheres appear unequal here because Antarctica is not shown.
Northern Hemisphere from above the North Pole
Northern hemisphere glaciation during the last ice ages. The setup of 3 to 4 kilometer thick ice sheets caused a sea level lowering of about 120 m.
Canadian Rockies in North America

Hurricanes and tropical storms (massive low-pressure systems) spin counterclockwise in the Northern Hemisphere.

Rapid intensification

Infrared satellite loop of Typhoon Maria in July 2018, as it underwent rapid intensification

In meteorology, rapid intensification is a situation where a tropical cyclone intensifies dramatically in a short period of time.

Atmospheric circulation

Large-scale movement of air and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth.

Idealised depiction (at equinox) of large-scale atmospheric circulation on Earth
Long-term mean precipitation by month
An idealised view of three large circulation cells showing surface winds
Vertical velocity at 500 hPa, July average. Ascent (negative values) is concentrated close to the solar equator; descent (positive values) is more diffuse but also occurs mainly in the Hadley cell.
The ITCZ's band of clouds over the Eastern Pacific and the Americas as seen from space
Diurnal wind change in local coastal area, also applies on the continental scale.

But every few years, the winters become unusually warm or unusually cold, or the frequency of hurricanes increases or decreases, and the pattern sets in for an indeterminate period.

Atlantic hurricane

Tracks of North Atlantic tropical cyclones (1851–2019)
The subtropical ridge (in the Pacific) shows up as a large area of black (dryness) on this water vapor satellite image from September 2000
Typical locations and tracks of tropical systems in June; blue is likely, green more likely, and orange most likely
Typical locations and tracks in July
Typical locations and tracks in August
Typical locations and tracks in September
Typical locations and tracks in October.
Typical locations and tracks in November.
Probability of a tropical cyclone of tropical storm or hurricane strength at a specific date, expressed as systems per 100 years
Atlantic accumulated cyclone energy (ACE) index from NOAA.
Atlantic Multidecadal Oscillation Timeseries, 1856–2013

An Atlantic hurricane or tropical storm is a tropical cyclone that forms in the Atlantic Ocean, primarily between the months of June and November.