When would you evacuate for a hurricane?


If wind force 12 is forecast in Germany, we have to be prepared for a storm with a speed of at least 118 kilometers per hour. However, the 12-point Beaufort scale is by no means sufficient to express the strength of a hurricane. Wind speeds of over 118 km / h are only the limit above which meteorologists speak of hurricanes at all. Therefore, a new scale - the Saffir-Simpson Hurricane Scale - had to be created for their classification. It was developed in 1969 and includes five levels that follow the Beaufort scale.

The namesake and developers were the engineer Herbert Saffir and Bob Simpson, then director of the National Hurricane Center (NHC). In the late 1960s, the World Meteorological Organization (WMO) worked on behalf of the United Nations on a study of building damage caused by storms. Saffir was in charge of developing a scale for classifying hurricanes. Simpson added information on storm surge levels accompanying hurricanes of each category.

The measure with which the strength of hurricanes is measured is the highest mean wind speed (MWG) occurring in their area. According to the recommendation of the WMO, the time average should be calculated over ten minutes. A short-term gust can falsify the mean value less than with a shorter measurement period. However, the meteorological services of the USA use the time average formed over just one minute. In the classification, the maximum MWG is the value most considered of a tropical cyclone. It determines the type and extent of the damage that may be caused, the wave height in the open sea and the height of the storm surge on the coasts. The MWG is a good indicator both for the air pressure near the eye and for the intensity of the air and water volume turnover and thus the precipitation. However, there is no connection between wind speed, core pressure and amount of precipitation.

Category 1: weak

Average wind speed (MWG): 118 - 153 km / h (32.7 - 42.6 m / s)

Air pressure:> 980 hPa

Flood height (storm surge above normal): 1.2-1.6 meters

Damage to trees, bushes and unanchored mobile homes or caravans. Possible flooding of coastal roads and slight damage to port facilities.

Category 2: moderate

Average wind speed (MWG): 154 - 177 km / h (42.7 - 49.5 m / s)

Air pressure: 980-965 hPa

Flood height (storm surge above normal): 1.7 - 2.5 meters

Damage to roofs, windows and doors of buildings. Greater damage to docks and caravans. Trees break down. Coastal and low-lying roads are flooded two to four hours before the storm center arrives. Small boats tear themselves from their berths, cars are swept away.

Category 3: strong

Average wind speed (MWG): 178 - 209 km / h (49.6 - 58.5 m / s)

Air pressure: 964-945 hPa

Flood height (storm surge above normal): 2.6 - 3.7 meters

Structural damage to smaller buildings, partial damage to house walls. Leaves are torn off, larger trees are knocked over, caravans and street signs are destroyed. Coastal flooding - Coastal areas that are 1.5 meters or less above sea level are under water 15 kilometers inland. Evacuations begin.

Category 4: very strong

Average wind speed (MWG): 210 - 249 km / h (58.6 - 69.4 m / s)

Air pressure: 944-920 hPa

Flood height (storm surge above normal): 3.8 - 5.4 meters

Severe damage to the walls and roofs of even larger buildings. Houses are damaged to the point of being uninhabitable. All trees and bushes are blown over. Trees are swept away hundreds of meters. Beaches are being eroded. Low-lying coastal roads are flooded three to five hours before the storm center arrives. Coastal areas that are less than three meters above sea level are flooded.

Category 5: devastating

Average wind speed (MWG):> 250 km / h (> 69.5 m / s)

Air pressure: < 920="">

Flood height (storm surge above normal):> 5.5 meters

Houses and bridges are destroyed, smaller buildings completely blown around or blown away. Ships are thrown hundreds of meters ashore. Coastal areas less than five meters are flooded up to 16 kilometers inland.

Status: July 2nd, 2004