Hurricanes

Hurricanes

Hurricanes summer is over and fall has arrived but many people to the south of us are observing another season hurricane season. According to the Montshire Museum of Science, hurricanes usually occur in the North Atlantic from June to November, with most of them in September. On average, between six to eight hurricanes form in the North Atlantic or North Pacific each year (Montshire), however, as many as 15 have occurred in the Atlantic in a single year. Hurricanes are powerful, whirling storms that measure several hundred miles in diameter. The winds near the center of a hurricane blow at speeds of 74 miles per hour or more (World Book, 400). Many hurricanes leave a trail of widespread death and destruction.

The definition of a hurricane, according to World Book Encyclopedia, is an area of low pressure that forms over oceans in tropical regions. Such a storm in the North Pacific Ocean is called a typhoon, and one in the South Pacific or Indian Ocean is called a cyclone. Most hurricanes originate within the doldrums, a narrow equatorial belt characterized by intermittent calms, light variable breezes, frequent squalls, and lying between the northeast and southeast trade winds (Encarta). Hurricanes consist of high-velocity winds blowing circularly around a low-pressure center, known as the eye of the storm. The low-pressure center develops when the warm, saturated air prevalent in the doldrums is under run and forced upward by denser, cooler air.

From the edge of the storm toward its center, the atmospheric pressure drops sharply and the wind velocity rises. The winds attain maximum force close to the point of lowest pressure. Encarta Encyclopedia states that hurricanes generally move in a path resembling the curve of a parabola. Also, that in the Northern Hemisphere the storms usually travel first in a northwesterly direction and in the higher latitudes turn toward the northeast. In the Southern Hemisphere the usual path of the hurricane is initially to the southwest and subsequently to the southeast. Hurricanes travel at varying rates. Those areas in which the hurricane winds blow in the same direction as the general movement of the storm are subjected to the maximum destructive violence of the hurricane.

According to the research team at Storm Central, hurricanes go through a set of stages from birth to dissipation. Tropical disturbance is the beginning of a hurricane, and it has no strong winds or closed isobars around an area of low pressure containing cloudiness and some precipitation. As the surface pressure begins to fall and winds increase to between 20 and 34 knots the tropical disturbances become tropical depressions. Tropical Depression has at least one isobar that accompanies a drop in pressure in the center of the storm. Surface winds increase to speeds of 35 to 64 knots. The storm becomes more organized and the appearance begins to resemble a hurricane because of the intensifying circulation around the center of the storm. This phase is called the Tropical Storm.

A tropical storm is stronger than a depression as the central pressure drops, resulting in several closed isobars at the surface. Some tropical storms only progress this far and die back down, several storms start out appearing as if they will be stronger and progress faster but lose their strength early on. However, if the storm proceeds it begins to take on the familiar hurricane appearance. This is a pronounced rotation which develops around the center core. The eye develops corresponding to the lowest atmospheric pressure near the center of the storm with spiral rain bands rotating around the eye of the storm. As surface pressures continue to drop, strengthening the pressure gradient of the storm, the storm becomes a hurricane when sustained wind speeds exceed 64 knots.

When a storm has advanced to the hurricane stage it can then be rated by the amount of strength that it has. This is done so by using the Saffir-Simpson scale, also known as the Simpson and Riehl Scale. The scale is a 1-5 rating based on the hurricane's present intensity. This is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall (Hurricane 99). Researchers at the Hurricane 99 weather site also say that, wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf in the landfall region. Well, if there is