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Hurricane Awareness Week
High Winds & Tornadoes
The intensity of a landfalling hurricane is expressed in terms of categories that relate wind speeds and potential damage. According to the Saffir-Simpson Hurricane Scale, a Category 1 hurricane has lighter winds compared to storms in higher categories. A Category 4 hurricane would have winds between 131 and 155 mph and, on the average, would usually be expected to cause 100 times the damage of the Category 1 storm. Depending on circumstances, less intense storms may still be strong enough to produce damage, particularly in areas that have not prepared in advance.
Tropical storm-force winds are strong enough to be dangerous to those caught in them. For this reason, emergency managers plan on having their evacuations complete and their personnel sheltered before the onset of tropical storm-force winds, not hurricane-force winds.
Hurricane-force winds can easily destroy poorly constructed buildings and mobile homes. Debris such as signs, roofing material, and small items left outside become flying missiles in hurricanes. Extensive damage to trees, towers, water and underground utility lines (from uprooted trees), and fallen poles cause considerable disruption.
High-rise buildings are also vulnerable to hurricane-force winds, particularly at the higher levels since wind speed tends to increase with height. Recent research suggests you should stay below the tenth floor, but still above any floors at risk for flooding. It is not uncommon for high-rise buildings to suffer a great deal of damage due to windows being blown out. Consequently, the areas around these buildings can be very dangerous.
The strongest winds usually occur in the right side of the eyewall of the hurricane. Wind speed usually decreases significantly within 12 hours after landfall. Nonetheless, winds can stay above hurricane strength as a storm passes over island land masses.
Tropical storms and hurricanes can also produce tornadoes that add to the storm's destructive power. Tornadoes are most likely to occur in the right-front quadrant of the tropical storm or hurricane. However, they are also often found elsewhere embedded in the rainbands, well away from the center.
Studies have shown that more than half of the landfalling tropical storms and hurricanes on the mainland produce at least one tornado, with some producing 50 or more. Evidence suggests that two tornadoes occurred on Kauai with Iniki, one near Hanapepe, the other near Wailua. In addition, it is believed a small tornado caused minor damage in Pearl City, Oahu as Hurricane Iwa was moving past Kauai. In general, tornadoes associated with hurricanes are less intense than those that occur in the Great Plains. Nonetheless, the effects of tornadoes, added to the larger area of hurricane-force winds, can produce substantial damage.
We have no way at presnt to predict exactly which storms will spawn tornadoes or where they will touch down. However, the four Doppler radars installed across the state of Hawaii greatly improves the forecaster's warning capability, but the technology usually provides lead times from only a few minutes up to about 30 minutes.
ADDITIONAL SAFETY INFORMATION