Physical Geography 101
Tropical Weather Systems
Tropical and Equatorial Weather Systems
Tropical and Equatorial Weather differs from Mid-latitude and High Latitude weather in the following ways:
Trough of low pressure.
Moves westward due to easterly Trade Winds.
Form between 2-30° Lat.
Showers form on the eastern side of the trough; converging winds forced to rise.
Occur along the Intertropical Convergence Zone.
Shifts with the seasons.
Small weak storms are often associated with these low pressure centers.
– very low pressure center
– high winds.
– central eye – calm center area storm.
– clear sky conditions common.
– highest wind speeds in eye wall
– intense precipitation
– Widespread wind and water damage
Stages of Hurricane Development
1) Tropical Disturbance - wind speeds <37 kph (23 mph)
2) Tropical Depression - wind speeds 37-60 kph (23-37 mph)
3) Tropical Storm - wind speeds 61-118 kph (37-73 mph
4) Hurricane - wind speeds >119 kph (>64 knots, >74 mph)
Always begin forming over warm, evaporating equatorial waters.
Release of latent heat is driving force (condensation).
Warm rising air creates low pressure.
Convergence and rising sustains this process.
No Coriolis effect at equator.
Weak Coriolis effect where most hurricanes begin development.
Coriolis effect increases as storm system moves poleward.
Faster spin rate develops.
Intensify low pressure.
Saffir-Simpson Hurricane Damage Potential Scale
|Scale Number||Central Pressure (mb)||Winds (mph)||Storm Surge (ft)||Damage|
|1||> 980||74-95||4 - 5||damage mainly to trees, shrubbery and unanchored mobile homes|
|2||965 - 979||96-110||6 - 8||some trees blown down; major damage to exposed mobile homes; some damage to building roofs|
|3||945 - 964||111-130||9 - 12||foliage removed; large trees blown down; mobile homes destroyed; some structural damage to small buildings|
|4||920 - 944||131-155||13 - 18||all signs blown down; extensive damage to roofs, window and doors; complete destruction of mobile homes; flooding inland|
|5||< 920||>155||> 18||severe damage to windows and doors; extensive damage to roofs; small buildings overturned and blown away; major damage to lower floors of all structures less than 15 feet above sea level within 500 meters of shore.|
1) Storm Surge
Dome or wave of water located at eye and radially away from eye.
Forms due to:
- Friction from wind pushing wave of water.
- Low pressure.
2) Wind Damage
High speed winds damage plants and buildings.
Tornadoes: embedded within thunderstorms within hurricane.
3) Inland Flooding
Hurricane prone areas: low coastal plains.
– typically have poor drainage.
Overwhelms inland area drainage networks.
Decrease in intensity and organization due to:
1) Movement over cold water – Cuts off supply of warm, evaporating water.
2) Movement onto land – Cuts off supply of warm, evaporating water.
3) Disruption of inward air flow.
Hurricanes form in Indian Ocean, parts of Pacific, and North Atlantic.
Hurricanes do not normally develop in South Atlantic or southeastern portion of Pacific Ocean.