Reading the weather station

On entering the weather station page, you will see a number of arrows showing where we have weather stations in place. If you move your mouse over a station, weather information for that station is shown in the information bar on the left hand side of the screen. Information presented here is a five minute average value for the five minutes prior to the time in the date tag. The "high" data shown for some variables is the highest value recorded within the five minute period.

Clicking on a station takes you to a web page that presents a few graphs showing what the weather did over the past few days which is very informative for those who want to follow weather systems currently influencing the region.

Below is a description of the data presented on the website.

Wind

Wind direction is often the source of much confusion. Is the arrow pointing to where the wind is blowing to or where the wind is blowing from? Think of the arrow as an old-style wind vane on a steeple. As the wind blows, the wind vane swings around to point into the wind, showing where it is blowing from. This is the convention that has been adopted by the general meteorological community. Thus the arrow on the web page points to where the wind is blowing from. When one hears that the south-easter is blowing in Cape Town, this means the wind is blowing from the south-east and the arrow on the web page should be pointing to the south-east.

Wind speed is in kilometers per hour.

Hi wind speed is the highest recorded gust speed in the five minute period from the direction as shown in the Hi wind direction.

Watch how wind direction changes with passage of weather systems over Cape Town. Also interesting is to observe how wind speeds and directions vary from place to place under the same wind regime as a result of the effect of the Cape Peninsula.

Temperature

Shown in degrees Celsius. It is very interesting to see how temperature varies spatially within the region as well as with height. During winter, dramatic temperature inversions can be seen between low lying stations (eg. COSAT) and higher lying stations (eg. UCT), sometimes up to 10 degrees.

Pressure

Shown in hecto-Pascals (hPa) or millibars. Pressure will vary with height between stations. In the time series graphs the passage of cold fronts and ridging high pressure cells is very evident.

Relative Humidity

Relative Humidity (RH) is a measure of the amount of moisture in the air. It is the ratio between how much moisture there is currently in the air and how much moisture there would be in the air if it were saturated. Saturated air has a RH of 100%. The "wetter"or "damper" the air feels, the higher the relative humidity; the "drier" the air feels, the lower the relative humidity. RH is very dependent on temperature.

Rainfall

Rainfall is measured in millimeters (mm) of rain.
Todays rain is an incremental measurement of rainfall from 00h00 to 23h59 of that day.
Monthly rain is the amount of rain recorded so far in the particular month and yearly rainfall is the amount of rain recorded in the particular year.
Rain rate measures how heavily it is raining. It is a calculated value showing how much rain would fall if it were to rain at that same rate for a full hour and is measured in mm per hour. A higher rain rate means it is raining more heavily.

Should you have any questions please contact us.