An intense rotating depression which develops over tropical ocean areas.
Typhoon Odessa, August 1985, 957 mb. Source: NASA
The weather associated with these storms is violent; torrential rain accompanied by thunder and lightning, severe turbulence within active convective cloud and frictional turbulence generated by strong winds. Static electricity may make navigation aids unreliable.
A Tropical Revolving Storm can cause significant damage to infrastructure and high loss of life. Areas affected by a significant storm can take months or even years to recover from the human, economic, and environmental damage. It is not uncommon for aircraft to be evacuated from an airport in advance of the landfall of a tropical storm. Damage and disruption to Airport and ATM infrastructure may render airports across a large area unusable, reducing the capacity and capability of ANSPs and closing, or reducing the capacity of, airports.
The diameter of a tropical storm is generally less than 500 nm and often only 100 nm in its early stages of development. With pressure frequently about 960 millibars, and often much less, the pressure gradient is such that winds regularly reach hurricane force.
The circulatory velocity of these storms is so great that, once formed, no frontal structure can persist and they become almost symmetrical circular depressions.
The factors which contribute to the intensity of a revolving storm are:
- Instability. Tropical revolving storms usually form close to the Inter Tropical Convergence Zone (ITCZ) where there is marked instability.
- Humidity. Storms mainly occur over the western parts of the tropical oceans where the air has had a long passage over the sea, or where air has crossed over from the other hemisphere, and has become saturated.
- Latitude. For a given pressure gradient the strength of the winds increases as the storm approaches the Equator.
- Temperature: Tropical revolving storms form over water surfaces with a water temperature of at least 27C.
The number and severity of storms in a particular season are also influenced by other climatological factors including El Niño effect
Tropical revolving storms mainly form over western parts of the tropical ocean areas
A tropical storm can only maintain its power when it is located over the warmest parts of the oceans - where surface waters are at 26°C or more. It will dissipate rapidly after crossing a coastline and moving inland, and it will lose energy more gradually if it strays into a region of cooler water.
Temperate Latitude Depressions Containing Residual Warmth and Moisture From a Tropical Storm
Even when tropical storm has dissipated, there frequently remain extensive remnants of very warm and moist air in the upper atmosphere. If this warm and humid air is absorbed into the circulation of a travelling Atlantic temperate-latitude depression it may provide sufficient added energy to cause a dramatic intensification of that depression, and this is undoubtedly the cause of some (but by no means all) of the severe September gales that have swept north-west Europe over the years.
Tropical Revolving Storms are known by different names in different regions of the world.
Tropical Revolving Storms are known as:
- Cyclones in the Indian Ocean, Bay of Bengal and Arabian Sea,
- Tropical Cyclones in the Southern Pacific,
- Typhoons in the China Seas, and
- Hurricanes in the Western Atlantic.
- Infrastructure Planning: Contingency plans should be in place to enable rapid restoration of ATM and airport services in the aftermath of a destructive tropical storm, in order to allow humanitarian operations and minimise economic disruption.
- Flight Planning:
- Operators need to keep a close watch on tropical storm development and progress and plan schedules accordingly. Crews need to consider the weather not only for the duration of the flight but also the time that the aircraft will subsequently be on the ground. Consider securing the aircraft if the aircraft are not to be evacuated.
- Changes in the movement of the storm can have a significant effect on the accuracy of forecast en-route winds and therefore crews should consider carrying extra contingency fuel if planning to fly close to such a storm.
- In the aftermath of a storm, crews should check NOTAMs to ensure that en-route alternates, affected by the storm, are capable of handling the flight in the event of a diversion.