Context : In this paper we present an analysis of wind speed , wind direction , relative humidity and air pressure taken at Telescopio Nazionale Galileo ( TNG ) , Carlsberg Automatic Meridian Circle ( CAMC ; now called Carlsberg Meridian Telescope ) and Nordic Optical Telescope ( NOT ) at Observatorio del Roque de Los Muchachos , in the Canary Islands .

Aims : Data are also compared in order to check local variations and both long term and short term trends of the microclimate .
Furthermore , influence of wind speed on the astronomical seeing is estimated to the aim to better understand the influence of wide scale parameters on local meteorological data .

Methods : The analysis is done using a statistical approach .
From each long series of data we compute the hourly , daily and monthly averages .
A particular care is used to minimize any effect due to biases in case of missing of data .
Wind direction is estimated by the annual percentage of the time in which the wind come from fixed directions .

Results : We found that relative humidity presents a negative correlation with temperature and pressure , while pressure is correlated to the temperature .
The three telescopes show different prevailing wind direction , wind speed , relative humidity and air pressure confirming differences in local microclimate .
We found that seeing deteriorates when wind speed is lower than 3.3 m s ^ { -1 } .
Comparison in terms of wind speed and high relative humidity ( > 90 \% ) shows that TNG seems to have optimal observational conditions with respect to CAMC and NOT .
Air pressure analysis shows that ORM is dominated by high pressure , that means prevailing stable good weather , as is to be expected from anticyclonic conditions .
Finally , short time variations of pressure anticipate temperature variations tipically by 2-3 hours , this property vanishes in time scales higher than some hours and disappear in longer time scales .

Conclusions :