1. Hurricanes
Aims: to investigate the causes and characteristics of Hurricanes/tropical revolving storms

2. Between latitudes of 5’ and 20’ north and south of the equator.
An atmospheric low pressure system that gives rise to roughly circular inward-spiralling wind motion, high winds and intense precipitation

3. The location of tropical revolving storms
They are usually located between latitudes 5-20’ north or south of the equator.
Warm tropical oceans (>26’C), where the ocean has been warmed to a depth of at least 50m. This is necessary to ensure sustained heating over a wide area which, in turn, provides a heat source to create a large mass of warm, unstable air.
They occur most commonly in autumn as this is when sea temperatures are at their highest, temperatures having built up over the summer.
They are found within the trade wind belt as this is where the surface winds warm as they blow towards the equator.
They travel westwards on unpredictable courses.
On landfall they move polewards and transfer heat away from the tropics
Away from their ocean heat source they rapidly lose power.

4. Hurricane formation

5. Hurricanes/Tropical revolving storms
Formation:
Hot seawater (27’C) heats the air above
Warm moist air begins to rise high and become unstable
A deep centre of low pressure is created and air is sucked in to replace the rising air
Winds increase to speeds of kph across a diameter of up to 600km
The ‘eye’ is a small area of calm where air is sucked down.
As the storm crosses over the land it loses power as its low pressure centre is filled in.

6. Atlantic hurricanes can be over 600km in diameter and are characterised by relatively uniform temperatures, pressure and humidity.
In late summer the ITCZ has moved north of the equator, heating wide expanses of the ocean to great depths. This warms the air above.
The convergence of air at low levels (the trade winds) and uplift from heating creates very low pressure and strong winds.
To develop from a depression into a tropical storm, the rising air currents must be maintained and this requires a constant supply of heat and moisture.
As winds sweep over the ocean surface they increase the rate of evaporation and the latent heat needed to transform liquid to vapour is transferred to the rising air. Later, as the moist air rises it will condense to form cloud and heavy rainfall, releasing latent heat and further driving the storm.
Once the storm has developed to a mature stage, a central eye develops with a diameter of 30-50km. This is an area of subsiding air, with light winds and high temperatures.
The descending air increases instability by warming the and serves to increase the intensity of the storm.
Wind speeds of km/hr are common. These can cause large scale damage and a significant threat to life. Associated with high winds are storm surges. These are pushed ahead of the storm and intensified by the rise in sea level allowed by intense low pressure. Intense rainfall can cause serious flooding.
Once hurricanes reach land they rapidly decline in energy due to the loss of its heat source, the warm oceans. Friction with the land decreases wind speeds. The average lifespan of a tropical storm is 7-14 days.