* Storm Hazards

What are tropical storms?

Huge spinning storms with strong winds and torrential rain.

How do tropical storms develop?

They develop over warm water.

As warm, moist air rises and condenses, it releases energy that increases wind speed.

What do scientists know about their formations?

They don’t know exactly how they’re formed but they do know the conditions needed.

What conditions are needed for a tropical storm?

• A disturbance near the sea-surface that triggers the storm (e.g. an area of low pressure)

• Sea water that’s warm (above 25’c to at least 50m below the surface) so lots of water will evaporate.

What other conditions are needed for a storm to form?

• Convergence of air in the lower atmosphere - either within the ITCZ or along the boundary between warm and cold air masses. This forces warm air to rise.

• Location at least 5’ from Equator.

Why do tropical storms not form 0-5’c either side of the Equator?

Because the Coriolis effect isn’t strong enough to make them spin.

Where do tropical storms form?

In the tropics because the water there is warm enough.

Where do tropical storms occur?

• Caribbean sea (called hurricanes)

• Bay of Bengal (called cyclones)

• China Sea (called typhoons)

• Northern Australia

When do tropical storms lose strength?

When they move over land because their supply of warm, moist air is cut off.

What direction do tropical storms initially move?

Move westwards due to the easterly winds in the tropics, e.g. trade winds move cyclones west across the Atlantic Ocean.

Why do storms move away from the Equator?

Because of the Coriolis effect.

What shape are tropical storms?

Circular, are hundreds of kilometres wide and usually last 7-14 days.

How do tropical storms spin?

Anticlockwise in the northern hemisphere, and clockwise in the southern hemisphere.

What is at the centre of the storm?

An area of very low pressure called the eye.

What surrounds the eye of the storm?

Rising air spirals around the eye in the eyewall, causing strong winds.

What is near the top of the storm?

There is an outflow of moisture-laden air, so cloud cover extends for a long distance either side of the eye.

How are storms classified?

Using the Saffir Simpson Scale, which is based on wind speed.

What is the highest category on the Saffir Simpson scale?

Category 5 (winds over 250km/h), and 1 is the weakest (120-150km/h)

What does the Saffir Simpson scale also estimate?

How much damage a storm of a given magnitude will do, from limited damage at category 1 to catastrophic damage at category 5.

How frequent are tropical storms?

Quite frequent - around one hundred occur each year.

Some of these never reach land, so they never develop into a major hazard.

Where and when are tropical storms more frequent?

In the northern hemisphere between June and November.

In the southern hemisphere between November and April.

What makes hazards created by storms largely irregular?

Because there are lots of factors that affect where and when a tropical storm will form and where it will hit land. So follow no clear spatial or temporal pattern.

How can certain cloud formations in tropical areas be identified?

From satellite imagery, and can be used to tell when a tropical storm is forming.

What can happen once it is clear a tropical storm is forming?

It can be tracked using satellite imagery and models, helping scientists work out when and where it’s likely to hit land.

The path of a tropical storm can therefore be predicted fairly accurately.