Ever wonder what factors come into play to create a hurricane? Hurricanes are tropical cyclones. When a tropical cyclone’s sustained winds reach 39 to 73 mph (63 to 118 km/h), it is considered a tropical storm and is named from an annual list from the World Meteorological Organisation.
Thus far for the Atlantic Hurricane Season we’ve experienced a tropical storm – Andrea and Hurricane – Barry. This year, the National Oceanic and Atmospheric Administration (NOAA) has predicted a near-normal season with a likely range of 9 to 15 named storms with winds of 39 mph or higher, of which 4 to 8 could become hurricanes including 2 to 4 major hurricanes (category 3, 4 or 5).
Wind Speeds of Hurricanes
Category 1: 74 to 95 mph (119 to 153 km/h)
Category 2: 96 to 110 mph (154 to 177 km/h)
Category 3: 111 to 129 mph (178 to 208 km/h)
Category 4: 130 to 156 mph (209 to 251 km/h)
Category 5: 157 mph or higher (252 km/h or higher)
At heart, hurricanes are fueled by just two ingredients: heat and water. Hurricanes are created over the warm waters of the Atlantic and Pacific Oceans, where the air above the ocean’s surface takes in heat and moisture. As the hot air rises, it leaves a lower pressure region below it. This process repeats as air from higher pressure areas moves into the lower pressure area, heats up, and rises, in turn, producing swirls in the air. Once this hot air gets high enough into the atmosphere, it cools off and condenses into clouds. Now, this growing, swirling vortex of air and clouds grows and grows and can become a thunderstorm.
Warmer waters mean lower pressures and a more unstable atmosphere which is conducive to hurricanes developing and intensifying. Another key factor is wind shear; the shift in wind direction with height into the atmosphere. Reduced levels of wind shear, which happens in the warm tropical Atlantic, provides a situation that promotes hurricane development.
Ultimately all these factors are guided by larger weather cycles particularly El Niño / La Niña. During an El Niño, in which ocean water around the northwestern coast of South America becomes warmer than usual, Atlantic hurricanes are suppressed, while La Niña creates more favorable conditions for hurricanes.
Now that you have a better understanding of the factors that result in hurricanes and tropical storms you can better anticipate adverse weather conditions and educate colleagues and customers.