Physical Science 101

Tropical and Equatorial Weather Systems

Differs from Mid- and High Latitude weather
1) Lack of strong Coriolis Effect
2) Lack of strong contrast between air masses - poorly defined fronts
3) Strong convectional movement of air masses - vertical movement
4) Evaporation and latent heat release are more important

Easterly Wave

Trough of low pressure.
Moves westward due to easterly Trade Winds.
Forms between 2-30° Latitude
Showers form on the eastern side of the trough where converging winds are forced to rise.

Equatorial Lows

Occurs along the ITC (Intertropical Convergence Zone).
Shifts with the seasons.
Small weak storms are often associated with these low pressure centers.

Tropical Cyclones

Same thing - different names


Characteristics include:
Very low pressure center
Central eye - not all hurricanes have this.
- a calm area in center of storm.
- clear sky conditions common.
- highest wind speeds in the eye wall
Intense precipitation
High winds
Widespread wind and water damage

Stages of Development

1) Tropical Disturbance:
2) Tropical Depression:
3) Tropical Storm:
4) Hurricane:

Hurricane Formation

Always begin forming over warm, evaporating equatorial waters.
Driving force is the release of latent heat, due to large amounts of condensation.
Release of latent heat continues to warm the air causing further rising of the air mass - creates low pressure.
Convergence and rising sustains this process.
No Coriolis effect at the equator
Weak Coriolis effect where most hurricanes begin development.
As the storm system moves poleward, Coriolis effect becomes stronger. Faster rate of spin develops. Helps to intensify the low pressure.

Hurricane Classification

Hurricane Damage

1) Storm Surge
A dome or wave of water located at the eye and radially away from the eye.
Forms due to friction from the wind pushes a wave of water onto land, and due to the low pressure in the center of the storm.
Greatest amount of damage

2) Wind Damage
High speed winds damage both plants and building, especially unsecured structures such as mobile homes.
Tornadoes often form embedded within the thunderstorms that form in the hurricane even higher wind speeds are possible.

3) Inland Flooding
Heavy amounts of precipitation
This overwhelms inland areas drainage networks.
Compounded by the fact that many hurricane prone areas are low coastal plains.
Typically have poor drainage.

Hurricane Decay

A decrease in intensity and organization due to:
1) Movement over cold water.
2) Movement onto land.
3) Disruption of inward air flow.

Hurricane Locations

Hurricanes form in the Indian Ocean, in parts of the Pacific, and in the North Atlantic.
Hurricanes do not normally develop in the South Atlantic or the southeastern portion of the Pacific Ocean.