Hurricanes Flashcards
Hurricane definition
Tropical cyclone with sustained one-minute winds of at least 74 mph (64 knots) at an elevation of 10 meters
Cyclone
large low-pressure system with circulating wind
Tropical disturbance
clusters of small thunderstorms
Tropical depression
presence of at least one closed isobar
Tropical Storm
Intensification of wind speeds of 37 mph
Hurricane Facts
- they are tropical cyclones with sustained winds at least 64 knots
- strongest hurricane on record has winds exceeding 190mph (Alan, 1980)
- Typically 500-1000km in diameter (smaller than mid-latitude cyclones)
- can be associated with heavy rains, tornadoes, and storm surges on the coast
Hurricane Season
- Hurricanes obtain their energy from latent heat release in the cloud formation process
- hurricanes occurs where deep layers of warm waters exists and during the times of highest SSTs
Hurricane characteristics
- high pressure air masses flow towards low-pressure zone
- wind created is deflected to the right Coriolis effect (counter clockwise rotation)
- tropical cyclones 5-20o latitude
Extra-tropical cyclone 30-70o latitude
Hurricane formation
- dependent on large area of warm water - min 26oC
- instability generated from storms in easterly trade winds, easterly waves
- move westward via winds
- 10% of tropical disturbances develop into organised rotating storms
- disturbance = depression if winds increase and warm moist air drawn in
Structure of a hurricane
- clouds and wind patterns
- warm moist surface water rises = rain bands (thunderstorms)
- sinking dry air = areas of fewer clouds
Structure of a hurricane: the Eye
- the eye is an area of descending air, relative clear sky and light winds which is about 25km in diameter on average
- a shrinking eye indicates storm intensification
- the eye wall is comprised of the strongest winds, the largest clouds, and the heaviest precipitation with rainfall rates as high as 2500 mm/day
- eye is fast moving - 20km/hr
Hurricane source areas
- deep water areas (several 10’s of metres)
- beyond 20oN, waters usually too cool
- Needs unstable atmosphere
- needs air movement via Coriolis effect (not present 0-5oN)
- disturbance = depression if winds increase and warm moist air (energy) drawn in
Wind shear
the difference in wind speed between the sea surface and upper surface and upper troposphere must be very low
- strong winds prevent development
Hurricanes in a warming climate
conditions necessary for hurricane formation restrict location to certain latitudinal boundaries
- hurricane ophelia in 2017 however hit as an extra tropical storm
Hurricane Debbie (1961)
- only tropical cyclone to ever hit Ireland/Britain whilst still considered tropical
- originated: tropical disturbance central Africa
- peak intensity of category 3
- peak gusts of 114mph
- power lines downed, buildings destroyed, agricultural losses, 18 fatalities
- very low pressure system over W. Ireland
