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Blowin' in the Wind, Issue #096 Know What Causes Hurricanes - August 1, 2012
July 31, 2012
Hello ,

Understanding What Causes Hurricanes

Hey, it's that time of year again. We know hurricanes are fascinating, and there have been numerous studies regarding their activity and what causes hurricanes to occur, the study of tropical cyclogenesis. Several different factors are needed to assemble the perfect atmosphere for a hurricane. And even if you get the right combination on the lock...once the atmospheric conditions are set up exactly as required, it may or may not lead to a hurricane.

For those interested in severe weather, understanding how hurricanes form is essential. They are common only in certain areas of the world. Generally known as cyclones, typhoons (Asia) and hurricanes (America) typically form in early autumn and late summer months, and only when the atmospheric conditions are perfect. Some people believe that warm ocean water causes hurricanes; that is the first of many ingredients which combine to create a hurricane.


There will need to be:
  • warm ocean water (26.5°C or greater down to a minimum of 50 metres),
  • sufficient Coriolis force (there is not enough right around the equator),
  • pre existing disturbance of some kind (called a focus - it provides a source of vorticity ),
  • low vertical shear (or else things rip to shreds before they form),
  • atmospheric instability, upper atmosphere divergence (to cause lift) and
  • moist mid atmosphere (to cause buoyancy).
If all of these factors occur in the right combination and storms and showers begin to happen, then low level winds need to move towards the center of the low pressure in the correct pattern. This gives the basic structure on which a new hurricane may begin to form.

As the cluster of convection forms a band, and if this becomes sufficiently concentrated, a large volume of warm air will rise and cool. As the air cools, the water vapor condenses, which releases a huge amount of heat into the air.

This increased temperature in the core decreases the air density, produces low pressure, and the wind intensity then has an opportunity to increase. If everything falls into place, these factors will cause a tropical storm to happen, which can produce winds of up to 74 mph, about 119 km/h. The winds need to be over this speed to classify as a hurricane, however, all of these contributing factors may be in place, and a hurricane may still not appear.

Equally as fascinating is the eye of the hurricane, and this feature causes the most discussion and research. The eye can be over 100 km in diameter, and typically can reach up to 350 km for large hurricanes. The air inside the eye is normally calm and tranquil even if the water surface below is turbulent, which is why the eye captures the interest of observers.

A bit more

People are often curious regarding what causes hurricanes, and there have been numerous studies to ensure that the facts about hurricanes are well publicized.

As those in affected areas know, the energy that is created by the hurricane is immense and can cause devastating consequences to property and land. The storms begin to lose energy as they move in land, therefore coastal areas see greater harm. Over 90% of the deaths that occur when a hurricane hits are caused by drowning in associated flooding, caused by hurricane-related precipitation and storm surges.

A limited number areas of the world are more prone to hurricanes than others; therefore, you shouldn’t be as worried unless you are in one of these locations. If you have reason to be concerned, you best bet might be a solid education about these systems. Here are a few helpful wikipedia articles:

General -

Formation -

Intensity Scale -

National Hurricane Center - Today's USA Hurricanes -

A bonus bit of humour - Top Ten Reasons Hurricane Season is Like Christmas

10. Decorating the house (boarding up windows).
9. Dragging out boxes that haven't been used since last season (camping gear, flashlights).
8. Last minute shopping in crowded stores.
7. Regular TV shows pre-empted for "specials".
6. Family coming to stay with you.
5. Family and friends from out-of-state calling.
4. Buying food you don't normally buy ... and in large quantities.
3. Days off from work.
2. Candles.

1 And the number one reason Hurricane Season is like Christmas...At some point you know you're going to have a tree in your house!

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