Odd Hurricane question

[NASA Fan]

I live near the coast, and recently a friend asked me something about how hurricanes form. He then started what he had heard, and it was a bunch of nonsense.

He said that it had something to do with the sand in the desert of Africa being picked up by the winds, and mixing over the ocean. He also said something about that Africa (maybe just the deserts) once was not as hot and dry, that there used to be water there.


I restrained myself from laughing too much at him, and explained how hurricanes really form.

I am trying to find out if he twisted a phenomena about one thing, into his misconception about hurricanes. Is there a weather phenomenon formed by winds in the desert (other than a sand storm) carrying sand to the ocean?

Thanks for any help anyone can provide.

[Jim]

Sorta right... kinda.

If a low pressure system develops over the Sahara, the prevailing (trade) winds will move it west, possibly over the Atlantic. Once over water, the system can pick up heat and moisture from the warm (if they are) ocean waters and develop further.

Sand is optional.

Here's a neat site that explains it with animation:
http://scifiles.larc.nasa.gov/kids/Problem_Board/problems/weather/hurricanebasics.swf

[geonuc]

Well, he is right about Africa once being not so hot & dry (glacier tracks have been found), but how on earth did he correlate that to hurricane formation today?

[jfribrg]

I don't think the sand has anything to do with it, but everything else is reasonably accurate about how atlantic hurricanes form. Usually, a wind storm moves west from nothwest Africa and picks up strength over the open ocean. If conditions are right (IIRC, the main condition is the absence of wind shear), then the winds associated with the storm increases the evaporation rate of the ocean water and the storm increases in intensity, which causes even more evaporation, etc. After a few days, the coriolis effect causes the counterclockwise (in the north atlantic) rotation and a tropical cyclone is formed. I don't think that the sand from the Sahara has anything to do with it. It may start as a sandstorm, but it is the wind associated with storm and the moisture from the warm ocean that produces the monster storm. I assume that sand storms come off of the Sahara in other times of year, but without a warm ocean, they don't cause any problems because the evaporation rate of the cold water is insufficient to produce the intense storms. I'm not sure what triggers cylones and typhoons to form in the Pacific and Indian oceans, but I'm sure that sand has nothing to do with it.

[Argos]

Conversely, Sahara´s dry air often take a toll on the development of storms. Tropical Storm Josephine, earlier this month, suffered from this phenomenon.

Related: Nasa Peers Deep Inside Hurricanes (http://www.sciencedaily.com/releases/2007/03/070307075649.htm).

[slang]

Here in Europe we will occasionally find a very thin layer of fine reddish dust on cars, and it is said to be Sahara sand.

[megrfl]

I live in south Florida, our meteorologists watch "waves" coming off the coast of Africa, which I assume is a low. These lows have over a thousand miles of open ocean to develope into tropical storms, then hurricanes if the conditions are right. Interesting fact for those who are amazed at the solar winds and etc.: Sustained winds at 25 mph, pretty bad, sustained winds at 70, holy crow. Winds are incredible!! When the media blows off, literally, a category 2 storm, and the reports of damage is minimal, the people who stayed experienced a very frightening 4 -24 hours.

[jokergirl]

There are some incredibly pretty satellite images of sahara sand being picked up and blown out over the ocean.
Here is one (http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17983) I could find with a quick Google search, although I know I have seen one of the sand going out over the Atlantic instead ofthe Mediterrannean as well.

It doesn't have anything to do with hurricanes though, apart from that wind is involved at some point.

;)

[Romanus]

Trans-Atlantic Saharan dust is a real phenomenon, important enough that its effects can be easily measured in the oceanic, terrestrial, and atmospheric realms. Even as far as my neck of the woods (Texas), Saharan dust can noticeably impact visibility in the summer. It doesn't help storms, though, in large part because its dry air is anathema to tropical cyclones. See:

http://www.aoml.noaa.gov/hrd/tcfaq/A17.html

The Sahara was indeed much rainier than it is today several thousand years ago, though by the time of the Pyramids it was about as dry as it's remained.

[NASA Fan]

Thank You for your help in clarifying.

[Ivan Viehoff]

The article on Tropical Wave on Wikipedia is informative. It makes the important point that while 60% of Atlantic hurricanes form as a result of one, that leaves 40%that don't. It is also worth bearing in mind that the NW Pacific is the most active hurricane zone (Atlantic is 3rd), and they don't have anything like the Sahara at an appropriate distance to the east of them. Haiti may have been hit by 4 tropical storms so far this season, but the Philippines has had 12...

[farmerjumperdon]

Lots of good stuff. For those looking for the real quick and dirty, hurricanes are an energy dispersion mechanism (EDM).

You can't make this stuff up. Well, you can, but the truth is more interesting.