Hurricanes/Storm Surges

A hurricane is a tropical cyclone with a warm core and winds that rotate at speeds of at least seventy four miles per hour. Most hurricanes originate within the doldrums (a narrow equatorial belt that has periods when it is calm, occasional light breezes, and frequent squalls; they lie between the Northeast and Southeast trade winds). Hurricanes occur in both the Atlantic and Pacific oceans, but only reach the north Atlantic because the doldrums don't extend far enough south in that area of the world. A hurricane is made up of high winds that swirl around the center of the storm, called the eye, which is usually about fifteen miles wide. For a hurricane to survive, the water temperature in the ocean must be at least eighty degrees Fahrenheit. The moisture from evaporating water from the surface of the ocean can also help give a hurricane energy.

The area just outside of the eye is called the eye wall. At the top of the eye wall (about 50,000 feet high) a lot of the air is propelled out which increases the upward motion of the air. Inside the eye, it is relatively calm. The clouds lift and the winds stop, but the water remains violent. Starting at the outside of the storm and moving in, the winds get stronger and the atmospheric pressure drops. The winds reach the greatest intensity at the eye wall before tapering off inside the eye.

Hurricanes can move at different rates, and they don't just move in straight lines. Usually hurricanes move in a parabola like curve. At low latitudes they usually move between five and twenty miles per hour. At higher latitudes they can move at speeds up to fifty miles per hour. The hurricane may be four hundred miles wide, and a single one can last for more than two weeks when it is over open water.

August and September are the months with the highest number of hurricanes, and in most of the world, hurricane season lasts from June to November. In the western Pacific, they occur year round. In the southern hemisphere, hurricane winds circle clockwise around the eye, and in the northern hemisphere, the winds circle counter-clockwise around the eye.The strongest hurricane that hit the western hemisphere in the 20th century was named Gilbert. It had a huge impact on Jamaica and parts of Mexico, in 1988. At times, Gilbert's winds were blowing at 218 mph

Hurricanes are rated on the Saffir-Sympson Hurricane Damage Potential Scale, shown below.

As a hurricane approaches land, the wind on shore becomes stronger, and the skies become darker. Lots of rain, highwinds, and storm surges may accompany the storm. As the hurricane comes nearer to the coast, the winds pick up, and propel it into the shore.

A storm surge is a rise in sea level above normal resulting from a hurricane or other intense storm.. When the hurricane is out over open water, there isn't really any storm surge. Instead, there is and "inverted barometer effect" which is where the sea level is slightly higher in the eye of the hurricane because of the lower atmospheric pressure. The storm surge only develops when the storm enters the coastal waters near shore, and can be between fifty and one hundred miles wide. The shallower the coastal water is, the higher the storm surge will be. Nine out of every ten people killed by hurricanes are killed because

The speed with which a hurricane hits the coast has a lot to do with the amount of damage inflicted. If a hurricane that is moving fast (fifteen to thirty miles per hour) hits the coast, the stress on the surface wind is greater in the RFQ, which creates a higher storm surge than would be created if the hurricane was moving slowly (zero to fifteen miles per hour).On the other hand, slow moving hurricanes can create greater floods because they have more time to pump water into the bodies of the storm surge.

The amount of damage done to a place from a storm surge depends upon the angle that the hurricane hit shore. The right front quadrant* (RFQ) is the part of the storm that is the strongest, so if a coast is hit by the RFQ, a higher storm surge will occur. When the RFQ hits first, the storm is hitting perpendicularly (south facing beach hit by a storm moving north, or a west facing beach hit by a storm moving east). If the hurricane moves parallel to the coast, a small storm surge, some winds, and rain, will occur, but the damage will not be as high because the RFQ will stay offshore. of water that lie inland. Also, the shallower the coastal water is, the higher the storm surge will be.

Around five hurricanes hit the United States coastline every three years. Only two of those hurricanes are likely to be major hurricanes (category three or higher).

The first photo is an aerial view of a hurricane, courtesy of http://wmatem.eis.uva.es/~marsan/discover/hurricanes/ The second two pictures are of hurricances hitting the shore and the damage they do, courtesy of http://www.continentalweather.com/Hurricane00407-NOAA-Ed.jpg and http://www. continentalweather.com/Hurricane00408-NOAA-Ed.jpg The fourth picture is of a stormsurge hitting a house, courtesy of http://www.continentalweather. com/StormSurge-Capitola98-02-08b.USGS-Ed.jpg

*The quadrants are set up the way they are in a coordinate graph, the right front quadrant of a hurricane is the quarter that is in the front and on the right side.