Hurricanes are a fact of life for coastal and even inland residents from Texas to Maine, and can sometimes affect the west coast as well. A few years ago, one hurricane even bothered Arizona!
A hurricane starts with a weather disturbance, warm tropical oceans, moisture, and light winds aloft. These conditions can lead to the heavy winds, storm surge waves, torrential rains, and floods we associate with hurricanes. Each year, an average of ten tropical storms develop over the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Many of these remain over the ocean. An average of six become hurricanes. In an average 3-year period, roughly five hurricanes strike the United States coastline, killing approximately 50 to 100 people anywhere from Texas to Maine. Of these, two are typically "major" or "intense" hurricanes (winds greater than 110 mph).
Amateurs have a long history of heavy involvement in the communication emergencies resulting from these storms. It is essential that ARES and/or RACES leaders understand and be prepared for the potential rigors of a major hurricane.
What is a Hurricane?
A hurricane is a type of tropical cyclone, which is a generic term for a low-pressure system that generally forms in the tropics. The cyclone is accompanied by thunderstorms and, in the northern hemisphere, a counterclockwise circulation of winds near the earth's surface. The tropical developments leading up to a hurricane are classified as follows:
ARES and RACES leaders must consider the type of storm defined above, and the track and speed of the storm in order to issue the appropriate alerts. Hurricanes are categorized according to the strength of their winds using the Saffir-Simpson scale. A Category 1 storm has the lowest wind speeds, while a Category 5 hurricane has the strongest. These are relative terms, because lower category storms can sometimes inflict greater damage than higher category storms, depending on where they strike, their forward speed, and the particular hazards they bring. In fact, even lowly tropical storms can also produce significant damage and loss of life, mainly due to flooding.
| STATUS | WINDSKNOTS | WINDS MPH | PRESSURE | STORM SURGE |
| Depression | <35 kts | <38 mph | ------ | ----- |
| Tropical Storm | 35-63 kts | 38-73 mph | ------ | ----- |
| Category 1 | 64-82 kts | 74-95 mph | 966 mb | > 4 - 5 ft. |
| Category 2 | 83-95 kts | 96-110 mph | 980-965 mb | 6 - 8 ft. |
| Category 3 | 96-113 kts | 111-130 mph | 964-945 mb | 9 - 12 ft. |
| Category 4 | 114-135 kts | 131-155 mph | 944-920 mb | 13 - 18 ft. |
| Category 5 | 136 kts+ | 156 mph+ | <920 mb | >18 ft. |
Table 7. Saffir-Simpson Scale
When the winds from these storms reach 39 mph (34 knots), the cyclone is given a name. The use of easily remembered names greatly reduces confusion when two or more tropical cyclones occur at the same time. Names are repeated on a five-year cycle, with different sets for Pacific and Atlantic storms.
The "storm surge" is simply water that is pushed toward the shore by the force of the winds swirling around the storm. This advancing surge combines with the normal tides to create the "hurricane storm tide", which can increase the average water level by 15 feet or more. In addition, wind driven waves are superimposed on the storm tide. This rise in water level can cause severe flooding in coastal areas, particularly when the storm tide coincides with the normal high tides. Because much of the United States' densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above mean sea level, the danger from storm tides is tremendous.
The slope of the continental shelf also determines the level of surge in a particular area.
Storm tides, waves, and currents in confined harbors severely damage ships, marinas, and pleasure boats.
Hurricane winds can deliver a "one-two" punch. When the storm first strikes an area, the winds are blowing in one direction. If the eye of the storm passes directly over the area, the "second half" of the storm will bring winds blowing in the opposite direction. Trees and structures that were weakened during the first "pass" are now more likely to fall or collapse as a result of the new forces in a different direction. Areas that are to one side or the other of the eye will not experience this effect.
One function of the National Hurricane Center and National Weather Service offices is to alert potentially affected residents in the target zone. These alerts must be received and acted upon immediately by ARES/RACES leaders. The government alerts are categorized as follows: