Tropical Cyclones and Hurricanes

Cyclones versus Hurricanes

What is the difference between a Cyclone and a Hurricane?

Not much really except one turns to the left and the other turns to the right. This seems to occur from being in different hemispheres. So in the Northern Hemisphere they will call them Hurricanes. Here in Australia we call them Cyclones.

Hurricanes are really Cyclones but are named differently because they are formed in the Atlantic Ocean. Storms that form north of the equator spin counterclockwise. Storms south of the equator spin clockwise. This difference is because of Earth’s rotation on its axis.

Each are rated as categories 1 to 5 with 5 being the strongest. The intensity is due to the wind power that is generated.

We can see the differences here with Cyclone Debbie that occured in March 2017 over Northern Queensland.

Here is Hurricane Irma.

Both have caused major destruction in regions hit, but Irma has hit more densly populated areas so the cost to rebuild will be much more than Debbie.

Tropical cyclones are described as “giant engines” that use warm, moist air as fuel. They form only over warm ocean waters near the equator. This is one of the issues, these Ocean waters are getting warmer and for longer periods greatly increasing the chance that more will be created in the future with increased intensity.

A tropical cyclone has many cumulonimbus clouds forming huge, circular bands. Air from surrounding areas with higher air pressure pushes in to the low pressure area. Then that “new” air becomes warm and moist and rises, too. As the warm air continues to rise, the surrounding air swirls in to take its place. As the warmed, moist air rises and cools off, the water in the air forms clouds. The whole system of clouds and wind spins grows, fed by the ocean’s heat and water evaporating from the surface.

As the storm system rotates faster and faster, an eye forms in the center. It is actually very calm and clear in the eye, with very low air pressure. Higher pressure air from above flows down into the eye.

When the winds in the rotating storm reach 80 kph, the storm is called a “tropical storm.” And when the wind speeds reach 150 kph, the storm is officially a “tropical cyclone,” or a “hurricane”.

Tropical cyclones usually weaken when they hit land, because they are no longer being “fed” by the energy from the warm ocean waters. However, they often move far inland, dumping many millimetres of rain causing flooding and causing property damage from the strong winds before they die out completely.

The big concern is that this is going to be a much more regular event due to Climate Change, man made or not. Reducing Risks with Storm events requires Government intervention with financing of risk mitgation, improved infrastrucure and much stronger Building Codes.