# Hurricanes, Tropical Cyclones and Typhoons

## What is the average size of the eye of a hurricane?

The average size (diameter) of the eye of a hurricane is 30 km (18.5 mi). The eye of the hurricane, a region of calm and light winds at the center of the storm, typically forms when the windspeeds reach 138 km/hr or 85 mph. The eye can be as small as a few km in diameter, or as large as 320 km in diameter (the diameter of Typhoon Carmen).

Source: NOAA

## What is the size of the typical hurricane/tropical cyclone?

Approximately 170 km (100 miles) wide. The size of the storm is determined by a balance of atmospheric forces, the two major ones being the Coriolis acceleration due to the rotation of the earth, and the low pressure region at the center of the storm. In order for hurricanes and cyclones to form and grow in size, the winds aloft ("wind shear") must also be low.

Source: NOAA

## Which hurricane/tropical cyclone was the largest?

The Great Hurricane of 1938 in the Atlantic Ocean, which was 800 km (500 miles) wide, may have been the largest. It was certainly the largest to strike New England and the northeast since the Great Colonial Hurricane of 1635. The 1-minute sustained wind speed of the Great Hurricane of 1938 was estimated to be 260 kilometers per hour (160 mph). The storm's central pressure was 940 millibars, compared to normal atmospheric pressure of 1013 millibars. The entire east coast of the United States was impacted, causing 600 to 800 deaths and \$306 million in damages (1938 US dollars).

## Which way do hurricanes/tropical cyclones spin?

North of the Earth's equator, hurricanes spin counterclockwise, when looking down from above the hurricane. South of the equator, hurricanes spin clockwise. The reason for this difference is the earth's rotation, which gives rise to what is known as the Coriolis acceleration, balanced by the low pressure at the center of the hurricane, typhoon, or cyclone. In fact, this spin direction of hurricanes is known as "cyclonic". The opposite spin direction is known as "anti-cyclonic".

## Which hurricane/tropical cyclone was the strongest?

It may have been tropical cyclone Olivia, April 3-12, 1996, at Barrow Island, Australia, which had peak wind speeds of 408 km/h (253 mph) as reported by the World Meteorological Organization. The storm's central pressures were around 925 millibars, some of the lowest pressures for such a major hurricane. 10 injuries were reported, along with about \$2 million damage in US dollars. Super typhoon Haiyan of November 6-9, 2013 may also rank as one of the strongest typhoons ever.

## Which hurricane/tropical cyclone lasted the longest?

Hurricane/Typhoon John in the Pacific Ocean lasted from August 11, 1994, to September 10, 1994, a total of 31 days. The affected areas were the Hawaiian Islands, Johnson Atoll, and Alaska. Damages were about \$15 million in 1994 US dollars. The storm's central pressure was recorded as 929 millibars, where normal atmospheric pressure is 1013 millibars. Maximum 10-minute sustained wind speeds were 155 kilometers per hour, about 100 miles per hour.

Source: NOAA and the WMO

## Which hurricane/tropical cyclone was the deadliest?

Probably the Bhola cyclone, 1970, Bangladesh, in which 300,000-500,000 people died. It was a category 3 tropical cyclone on the Saffir-Simpson scale.