Why Are Hurricanes So Rare InThe Southern Hemisphere?

[ralph124c]

Brazilhas just been visited by a cyclonic storm (it hit the coast of Sanat Catarina) with winds >75 MPH. The US Weather service calls this a hurricane (the Brazilians didn’t). Anyway, the Norther Hemisphere has (usually) 5-12 hurricanes a year-why are they so rare in the South?

[Laughing_Lagomorph]

When you refer to 5-12 hurricanes a year in the Northern Hemisphere I think you are referring to Atlantic storms. Other parts of the world get similar types of storms but they are called typhoons or cyclones, depending on where they are.

With respect to your OP I would point out that there is less land mass in the Southern Hemisphere than in the Northern, so there are fewer places for ocean storms to come ashore. Also I think there are fewer people in the Southern Hemisphere than the Northern, so you are less likely to hear about storms down there because they (very generally) affect fewer people.

[PigBoy]

I have this book from USA Today called The Weather Book, with all kinds of pretty pictures and graphics explaining all kinds of weather phenomena. From the chapter on hurricanes I see this:

In fact, winds above the tropical Atlantic often blow from the west, opposite the direction of the low-level winds, or blow too fast to allow hurricanes to develop. This accounts for the relatively small number of disturbances that become hurricanes. Such unfavorable upper-air winds are probably why tropical storms don’t form over the South Atlantic, between Africa and South America, and over the southeastern Pacific, off the South American Coast. These are the world’s two tropical oceans that don’t produce hurricanes.

There’s also a little map showing the average distribution of tropical storms by region as a percentage of the total number in the world. Here are the numbers it gives:

East Pacific Ocean 15%
Western Atlantic Ocean 12%
North Indian Ocean 12%
Western North Pacific Ocean 30%
South Indian Ocean 12%
North and west Australia 7%
South Pacific Ocean 12%

So if that map is something close to correct, about 31% of the storms (the last three in the list) occur in the Southern Hemisphere, just not in the two areas talked about above.

[dqa]

From Weather Underground:

The South Atlantic is not prone to tropical cyclones because there is strong vertical wind shear between the surface and the upper atmosphere. This shear tends to tear storms apart before they can form. In addition, there is typically no inter-tropical convergence zone (ITCZ) over the South Atlantic. Without an ITCZ to provide thunderstorm activity and an initial spin, tropical cyclones never get a chance to form.