Consider what your main argument or hypothesis regarding the spacing of isobars and wind speed will be. Think about your goals pertaining to the general statement. Do you want to inform a novice audience about this phenomena or do you want to introduce possible problems with the study of wind speed?
Write a thesis statement. This statement will set the tone for the rest of the general statement. If you are writing a statement that educates the public, simply state the observed relationship between the spacing of isobars and wind speed. For example:
"The spacing of isobars and wind speed are intimately connected. The closer the isobars are to one another, the faster the wind speed."
Follow up on the introductory thesis statement by giving some general information surrounding the topic. For example, you could discuss the approach meteorologists use to measure the distance between isobars to determine wind speed. Another topic to discuss in the general statement would be the centrality of understanding wind patterns on world weather patterns.
Keep the general statement to one paragraph, and possibly two if you have a lot of information. A general statement should simply introduce the reader to the wider literature on the topic of wind speed and isobars.