A wind rose is a graphic tool used by meteorologists to give a picture view of how wind speed and direction are typically distributed at a particular location. In most parts of the world strong winds usually come from certain directions and the frequency of winds from each direction varies throughout the year.
This can be extremely useful information for sailors when planning a trip in advance. You get an idea of the conditions you are most likely to find. The length of each “spoke” around the circle is related to the frequency that the wind blows from that direction.
Historically, wind roses were predecessors of the compass rose found on charts. They were included in order to let the sailor know which directions the major winds in an area blew.
A more modern use for wind roses today is when designing airport runways, as aircraft perform their most optimal take-offs and landings pointing into the wind.
Presented in a circular format, a wind rose shows the frequency of winds blowing from particular directions. Remember that winds blow FROM a direction but currents flow TO a direction. So a northerly wind and a northerly current are going in opposite directions.
The data from which wind roses are produced has been collected over a period of many years – sometimes going back to the 19th century.
This data came from a numerous sources, including automated observation platforms, ships’ logs, meteorological services, and scientific research projects. It was collected from all types of equipment, ranging from those found aboard 19th century ships to sophisticated electronic equipment on modern research vessels. Needless to say there are errors and discrepancies in the data due to the varying quality of the input sources and changes in observing practices over time.
Wherever possible these have been corrected by the National Oceanic and Atmospheric Administration (NOAA) to increase the accuracy of the data upon which the wind rose is based.
If you are planning a sailing holiday in Greece or Turkey you’ll find wind roses for this area on the Sailing Issues website. This is a very useful site with many resources for the Mediterranean sailor.
You will find links to wind roses for each month of the year shown on the appropriate part of Greece here. The wind roses shown are a little different from those commonly used at airports and other locations but they are fairly simple to read.
Click here for the page leading to the wind roses in Sailing Issues. You can see an example of the wind roses shown used below – they include information on normal Beaufort wind speeds in each direction.
Percentage of calms: The number in the centre of the circle represents percent occurrence of calms for a given month.
Percentage occurrence of wind in eight compass directions: The length of the 8 lines radiating out from the circle indicates the percent occurrence of winds from each compass direction. The longer the line the higher the occurrence from that direction. If the length of the line exceeds 30 percent, the actual percentage (in the example:31 percent from the west) is displayed.
Beaufort wind force: The number of feathers on the line indicates the Beaufort force of the wind from that direction. Each small feather equals 1 Beaufort of wind force. If the Beaufort wind force exceeds force 6, a single large red arrow is displayed instead of the individual feathers.
These wind roses are useful when planning a week or more cruising as you can see how likely it is that you can make your planned route without having to spend a lot of time beating against the prevailing wind.
Remember that wind roses only tell you what is normal for the time of year you intend to sail in an area. You will need to back this up with local knowledge and weather forecasts each day. Some areas, such as the Saronic, can have wind blowing from the north in the morning and from the south in the afternoon!