Defining Hurricanes and their Characteristics

Hurricanes and other cyclones that form in the tropics during the summer time and fall are very different from the tropical storms that form during the winter. Both types of storms are able to produce very strong winds and flooding rain. There are seven main characteristics that define a tropical hurricane and they are that hurricanes have no fronts and the winds weaken with height. The centers of the hurricane are warmer than their surroundings and they form under weak high altitude winds. The air also sinks at the center of a hurricane\and the main energy source is the latent heat of condensation. The last main characteristic of a hurricane is that they weaken rapidly over land. During the last third of the 20th century, floods and landslides from heavy rains were the leading cause of hurricane and tropical storm deaths.

To make the best analysis of available data regarding hurricanes, one must be familiar with the normal wind pressure, temperature, clouds, and weather patterns associated with them. No two hurricanes are exactly the same and there are great variations between each one. Certain general features will appear with sufficient frequency to permit mean pattern classifications. These features serve as a valuable guide in reconstructing the picture of an individual hurricane from sparse data. Since meteorological elements are not distributed uniformly throughout all sections of hurricanes, it is customary to describe the storms in terms of right and left semicircles or four quadrants. The division into semi circles is along a line extending through the center of the cyclone and in the direction toward the storm.

The surface winds of a hurricane will blow inward in a counterclockwise direction toward the center. The winds in the left rear quadrant have the greatest angle of inflow. The diameter of the area affected by hurricane winds may be in excess of 100 miles in large storms or as small as 25 miles in smaller storms. Gale force winds can cover an area of 500 to 800 miles or even more. The maximum extent of strong winds is usually in the direction of the major subtropical high-pressure center. This is most frequently found to the right of the storm’s path in the Northern Hemisphere. Surface wind speeds of over 140 knots have been successfully recorded, but the accurate measurements of peak wind speeds have not been possible with any reliable degree of accuracy.

The sea level isobars are an excellent tool to analyze hurricanes. The isobars take on a symmetrical or elliptical shape. In contrast to extra tropical cyclones, the tropical cyclones show no cooling toward the storms center. This indicates that the horizontal adiabatic cooling caused by lower pressures and is largely offset by the heat added through the condensation process. The cloud patterns of tropical cyclones also differ from those of extra tropical cyclones. In mature tropical cyclones, all of the cloud forms are present, but the most significant clouds are the heavy cumulus and cumulonimbus clouds, which spiral inward toward the outer edge of the eye. The eye of a storm is one of the oddest phenomena knows in meteorology. Precipitation ceases abruptly at the boundary of a well-developed eye, the sky clears, the sun or stars become visible, the wind subsides to less than 15 knots, and there is a dead calm.

In mature storms, the eye’s diameter averages about 15 miles, but it may attain over 40 miles in large typhoons. The eye is not always circular and sometimes it becomes elongated and may appear to have a double structure appearance. The eye is constantly undergoing transformation and does not stay in a steady state.