Tropical Cyclone

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Tropical Cyclone
warm-core, low-pressure system that develops over the tropical or subtropical water with winds of at least 120 kph
Hurricane Mitch
killed 20,000 people, mostly associated with slides caused by torrential rains
Great Bhola Cyclone
hit Bangladesh in 1970, causing 500,000 deaths in a very populated region below sea level
Galveston Hurricane 1900
Deadliest US hurricane: 8,000 deaths
Average hurricanes in Canada yearly
4 hurricanes
Deadliest Canadian Hurricane
1775 when 400 people died on Newfoundland Coast
Economic Impact
Rebuilding of damaged infrastructure, evacuation, energy production, severe costal erosion
Katrina
New Orleans is below sea level with levees built to keep water out of the city, but storm surge broke the levees and caused the worst case scenario
Hurricane Andrew 1992
People were unprepared, Andrew hit about 10-15km outside of Miami
tropical cyclone in Atlantic Eastern Pacific Oceans
hurricane
tropical cyclone in Western Pacific
typhoon
tropical cyclone in Indian Ocean
cyclone
Warm core
the warmest air is at the center of the storm
Mechanism: Latent heat release
heat resulting from water condensing (gas to liquid), warm moist air rises from the bottom of the eyewall, then condenses into water and warms the surrounding air. as air continues to rise, wet air takes it's place
Mechanism: Compression/subsidence
as air in the sinks, it is warmed due to compression and then pushed back up creating strong convection currents
tropical depression
first appearance of a lowered pressure and organized circulation in the center occurs, winds are 20-34 knots
tropical storm
storm becomes more organized and banding starts to occur, winds are 35-64 knots
hurricane
clear eye, with spiral rain bands, winds reach 64 knots
hurricane structure
winds circulating into the center of the storm and raising in a spiral, a lot of air in a low pressure system,
coriolis effect
objects diverted in their natural course because of the rotation of the earth. in a low pressure system, winds attempt to blow into the rotation of the earth
the eye
the hurricane center is relatively calm
the eyewall
region of thick clouds surrounding the eye, most dangerous area of the storm, the deeper the clouds in the eyewall, the stronger the storm
rainbands
curved bands of clouds that train away from the eye that are capable of producing heavy bursts of winds and rain
tropic cyclone size
hurricanes are 300 miles wide, can be up to 1000 km
Saffir-Simpson Intensity Scale
scale that measures wind speeds
category 5 hurricane
winds greater than 155 mph
When do they form?
Late summer and fall when the water temperatures are the warmest
Where do they form?
Do not form near equator, curve to the north and east, usually along warmer East coast of continents
Six key hurricane facts
2/3 occur in the Northern Hemisphere (warmer), never develop within 5 degrees of the equator: no coriolis force, hurricanes rarely form north or south of 25 degrees, 50%-70% of annual tropical storms turn into hurricanes, western pacific in the northern hemisphere produces the most tropical cyclones, hurricanes don't form in the south Atlantic and southeast Pacific (with the exception of one recently off coast of Brazil)
Four main sources of Tropical cyclone
Enough coriolis force to develop a low pressure center, a pre-existing low-level focus or disturbance, warm sea surface temp, and low vertical wind shear
Three trigger mechanisms:
Intertropical convergent zone, easterly waves, middle latitude cold fronts
Intertropical convergence zone
migrates with the sun towards the summer hemisphere
Intensity
warmer ocean to create low pressure system, depth of heat in water plays a role: winds create turbulence and mix warm and cool waters that strata each other, they bring cold water to the surface and lose energy, and wind shear at the bottom must be equivalent to those at the top: weaker wind shear= stronger hurricane
Hurricane Hazards
Storm surge, wind damage, heavy rains, associated tornadoes, flooding
storm surge
wide, large dome of water that sweeps over the coastline
what creates storm surge?
strong onshore winds and relatively low air pressure
heavy rains
rainfall isn't dependent on the intensity of the hurricane
Galveston Hurricane 1900
city was raised 9 feet and texas wasn't prepared; ignored Cuban weather warnings
Isaac Cline
hurricane expert who contributed to the city's complacency by dismissing the notion that a hurricane could destroy Galveston
Flooding-Floyd 1999
16-20 inches of rain that produced extreme flooding, 4 billion in damage, thousands of jobs lost, flooding created significant problems for the North Carolina's rivers