11: Hurricanes and Tropical Cyclone Winds Flashcards
what is the tropical cyclone evolution
cyclone –> tropical low –> tropical disturbance –> tropical depression –> tropical storm –> hurricane –> typhoon
what is a cyclone
rotating weather system wiht low pressure in its center and rotates counterclockwise in N hemisphere
what is tropical low, disturbance, and depression
- tropical low: surface low pressure system in tropics
- tropical disturbance: tropical low with clustre of thunderstorms and weak surface winds but no rotation
- tropical depression: rotating tropical low with sustained surface winds of 20 to 34 knots
what is tropical storm, hurricane, typhoon, tropical cylclones
- tropical storm: tropical cyclone with maximum sustained surface winds between 34 and 64 knots
- hurricane: tropical cyclone with sustained surface winds exceeding 64 knots
- typhoon: same as hurricane but in the pacific ocean west of the date line
- tropical cyclones: hurricanes and typhoons in the Indian and south pacific oceans
etymology of hurricane and typhoon and how are hurricanes named
- hunrakan: mayan god of storms
- huracan: carb tribe’s god of evil
- urican: word for big wind
- huracan: spanish
- typhon: greek for monster
- t’ai fung: contonese for great wind
- hurricanes named using a repeating 6 year list
hurricane structure (5)
- counter clockwise spiralling in low levels
- clockwise spiralling out at top
- cloud free eye in centre shows dry descending air
- eye wall of numbus clouds with heavy rainfall
- spiralling precipitating rainbands
- image 26
necessary tropical cyclone environment (5)
- SST (sea surface temperature) >26C for sufficient latent heat release
- ocean mixed layer depth >60m necessary to inhibit upwelling of cold water due to hurricane mixing
- weak vertical wind shear necessary to concentrate latent heat release
- more than 5 degrees latitude away from equator to initiate rotation
- landfall and jetstream encounteres can cause dissipation
trajectories of tropical cyclones, tyhpoons, and hurricanes
- tropical cyclones: Indian ocean area (from equator to India (north) and from equator to madagascar (south) and from equator to australia
- hurricanes: east US like florida from equator and west US like California from equator
- typhoons: east of japan from typhoon
cause of storm surge
- onshore wind causes a dome of water to move shoreward, causing destruction
- caused by low pressure waether systems like tropical cyclones and hurricanes
what is the hurricane intensity scale called
- saffir simpson scale
Category 1: minimal damage
Category 2: moderate
Category 3: extensive
Category 4: extreme
Category 5: catastrophic
hurricane trajectory characteristics
- tracks seem erratic
- move westward in tropics
- curve northward
- move northeast in mid latitudes
why are storm surges highly destructive
- due to drag force
- drag force formula proportional to pV^2 (where p is density and V is velocity)
What is the cone of uncertainty and what info does it not provide
represents the probably tracks of the center of a tropical cyclone. doesnt provide amount of rainfall, wind speeds, tornadoes or storm surge
how are wind speed probabilities detemrined
dervied from 1000 realizations that incorporate random samples of historical track and intensity forecast errors made in the last 5 years. weakening effect of land on tropical cyclones also considered
how is wind risk determined
- wind speed probability text product (PWS) made according to gridded output from the wind speed probability technique
- text product contains onset and cumulative probabilities for a fixed set of locations
- locations are large cities, isands, and ofshore sites
- the cumulative probability (given inside the brackets) is the wind risk
