The database of the HWind project sponsored by the National Oceanic and Atmospheric Administration (NOAA) for hurricanes between 1994 and 2013 is analysed. Moreover, the wind speed of Hurricane Sandy is studied.
Hurricanes are among the most destructive natural hazards, not only in terms of human life, but also on built infrastructure 
. Since their consequences are devastating, the effects of these winds on structures such as bridges, transmission lines, offshore wind turbines, skyscrapers, or water supplies are the subject of research 
. However, the most common constructions are usually low-rise buildings, where the direct impact perceived by most of the population is on the building roofs 
. Moreover, coastal economic activities, such as fisheries, are affected 
. Last but not least, the longest-lasting consequences are observed on human health 
Due to their global impact, hurricanes have been studied in numerous analyses, some of which, such as the relationship between pressure or temperature and wind, are experimentally based 
. Other studies consider the vertical wind profile 
, which is extremely useful for evaluating the structural safety of buildings in extreme wind conditions. The hurricane trajectory analysis is one line of research 
, with other studies focus on gauging their size 
. Theoretical research has also occasionally been conducted 
Due to the close link between ocean surface temperatures and hurricanes, Hosseini et al. 
obtained a high correlation between sea surface temperature, the increase in which was attributed to climate change, and hurricane frequency over the last century. Another consequence of recent atmospheric warming might be the decrease in translation speed and the increase in the rain rate 
. However, Rojo-Garibaldi et al. 
reported a decreasing trend in the number of hurricanes in the Gulf of Mexico and the Caribbean over a wider period, 1749–2010, which they correlated with sunspot activity.
2. Wind Speed Analysis of Hurricane Sandy
2.1. Database Analysis
Chavas et al. 
presented the spatial distribution of hurricane tracks on the Earth in the period 1999–2009 where the lowest number was observed over the Southern Pacific Ocean and Southern Indian Ocean. In the remaining basins, these trajectories were similar for the Atlantic and East Pacific basins. In both regions, hurricanes approached the continent from low latitudes, then veered and moved away from the continent to higher latitudes, with the greatest latitudes being reached in the Atlantic basin. However, hurricanes in the West Pacific basin were confined to low latitudes.
Delgado et al. 
reanalysed the North Atlantic hurricane database for the period 1954 to 1963. They obtained an average of around 11 storms (tropical storms and hurricanes) per year, with the number varying between 7 and 16. This average was around six for hurricanes each year, ranging between three and nine, and around three per year for major hurricanes, ranging between none and five.
Most hurricanes described in Section 3.1
occur in the second part of the year. This result is in agreement with the study presented by Corporal-Lodangco and Leslie 
, who investigated tropical cyclones in the Philippine region during the period 1945–2011. They reported two seasons: the less active season, from January to May, with a median seasonal frequency of two, and the more active season, from June to December, with a median seasonal frequency of 15. However, although hurricane seasons are usually felt to exist, their start is not fixed since this may be influenced by atmospheric processes. For example, a significant delay in the start of the hurricane season in the western North Pacific was observed after a strong El Niño in the preceding winter 
Anomalies in the sea surface are responsible for changes in hurricane frequency. Wang et al. 
investigated Atlantic hurricanes from 1951 to 2010 and concluded that warm anomalies in the sea surface temperature in wintertime in the main Atlantic development region are frequently followed by unusually active hurricane seasons. Moreover, the hurricane frequency may be affected by certain trends, since analyses of cyclone genesis frequency from October to December over the western North Pacific revealed a decreasing trend with two periods, the first from 1980 to 1995, with about ten hurricanes per year, seven of which could be assigned to the eastern region, and the second from 1996 to 2011, with about six hurricanes per year, where around four may be assigned to the western region 
. Another factor that may impact on this frequency could be climate change, since analyses of the strength and distribution of hurricanes during the 2016 North Atlantic hurricane season revealed that said year was noticeable for a series of events never before observed, such as the observation site for a high category or the number of high category hurricanes in the same month 
2.2. Wind Speed
These measurements have occasionally been taken if the experimental device is near the hurricane route 
. In these situations, the wind speed gradually increases to the maximum, and then decreases once the hurricane centre moves away from the experimental site. Although measurements are taken at a single point, they may be considered similar at sites that are an equal distance from the centre, since radial symmetry is assumed. Moreover, studies normally present the horizontal wind speed profile, where one maximum is reached at a certain distance 
, and this wind speed shape has occasionally been modelled 
Although analyses of wind speed distribution are not common, the current study considers the Laplace distribution of the wind speed due to the shape of the wind speed histogram. However, Cui and Caracoglia 
used the Weibull distribution for annual wind speed maxima.
For US tropical cyclone forecast centres, estimating the maximum extent of the 17.5, 25.7, and 32.9 m s−1
(34, 50 and 64 kt, respectively) winds in compass quadrants (northeast, southeast, southwest, and northwest) surrounding the hurricane centre is critical 
. These wind thresholds are known as gale-force, destructive, and hurricane-force, and the corresponding distances are called the “wind radii”. The average 17.5 m s−1
wind radius calculated in 2014–2015 in the western North Pacific basin was around 248 km, larger than those for the Atlantic and eastern North Pacific basins, which were around 176 and 152 km, respectively 
Chavas and Emanuel 
analysed the azimuthally-averaged radius of 12 m s−1
, and the radius of vanishing winds, r0
, for a dataset covering the period 1999–2008. Their global median values were 197 and 423 km, respectively. Moreover, they presented these values in each basin. The largest radii were reached in the West Pacific basin, around 250 and 500 km, whereas the smallest values were observed in the East Pacific basin, slightly below 150 and 350 km.
2.4. Air Parcel Trajectories
Wind speed vertical profiles in the boundary layer modelled by Snaiki and Wu 
revealed the noticeable influence of the surface below 300 m, where the change is around 5 m s−1
. Shu et al. 
presented the wind speed profile in the troposphere, with the maxima being reached at nearly 1000 m height and close to 35 m s−1
Myers and Malkin 
presented the spiral trajectory of air parcels in a hurricane and Niu et al. 
considered its mathematical form by a logarithmic spiral. Spirals observed in trajectories at low altitudes may be attributed to friction with the surface, whereas loops in the mid troposphere may be due to a composition of the wind rotation and the hurricane displacement.
This entry is adapted from 10.3390/atmos12111480