Part 4. Disturbances Chapter 12 Tropical Storms and Hurricanes

Introduction Hurricanes are responsible for astonishing amounts of property damage and loss of life in many regions of the world Propagation of Hurricane Andrew Andrew caused major damage in Florida and Louisiana

Hurricanes around the globe Atlantic - hurricanes Western Pacific – typhoons – highest frequency region Indian Ocean and Australia – cyclones South Atlantic - almost none

Tropical cyclone genesis areas and related storm tracks

The tropical setting where tropical storms usually form Subsidence (trade wind) inversion on the east side of the subtropical highs traps cooler, moist air (marine layer) at the ocean surface On the western sides of the ocean basins, the marine layer tends to be warmer and thicker due to higher ocean temperatures -- more hurricanes tend to develop here

Tropical cyclone structure Hurricane characteristics –Sustained winds greater than 120 km/hr (74 mph) –Average diameter = 600 km (350 mi) –Central pressure = ~ 950 mb to 870 mb

Vertical temperature profile across a hurricane Hurricane eye -- average diameter = 25 km (15 miles) -- area of descending air -- strongest winds in eye wall (clouds just outside eye)

Tropical cyclone air trajectories with height

The double eye wall of Hurricane Emily Hurricane with a double eye wall (occurs near maximum strength) eye walls

Hot tower in Hurricane Rita A hot tower is a part of the eye wall that rises to great height (up to 36 km); it can indicate hurricane strengthening

Hurricane Formation Steps in the formation of hurricanes Tropical disturbance associated with an easterly wave in the upper air winds Tropical depression -- at least one closed isobar Tropical storm -- winds greater than 37 mph Hurricane (typhoon, cyclone) -- winds greater than 74 mph

An easterly wave

Conditions Necessary for Hurricane Formation Warm ocean water (> 27 o C (81 o F)) –Latent heat release Most frequent in late summer and early autumn –Formation equatorward of 5 o Unstable atmosphere without vertical shear Once formed – self-propagating system until it runs out of warm water

Erratic hurricane path examples Hurricane paths are controlled by trade winds, upper air flow, air pressure systems and ocean temperatures; they can be quite erratic.

After it came onshore, hurricane Camille merged with a frontal cyclone along a stationary front, causing massive loss of life and property damage due to heavy rains and flooding.

Predominant Atlantic hurricane paths

Hurricane Destruction and Fatalities are caused by several factors: Wind Heavy rain Tornadoes Right front quadrant Storm surge Rise in water level associated with pressure drop

Wind speed variations by quadrant

Blown sand from Hurricane Katrina

Average tornado locations relative to hurricane storm center

Atlantic hurricane frequencies

End of Chapter 12 Understanding Weather and Climate 4th Edition Edward Aguado and James E. Burt