In Part I of the two-part paper, we describe the results of a field program that was especially designed for testing the results of a theoretical model. The observations included measurements by an instrumented aircraft and a special surface network over an island with physical features that satisfy approximately the model assumptions. Panoramic cloud photographs and time-lapse movies of the clouds were also taken. The observations show that evaporational cooling of the environment has an important, influence on the behavior of perturbations induced by the heated island. Abstract In Part I of the two-part paper, we describe the results of a field program that was especially designed for testing the results of a theoretical model. The observations included measurements by an instrumented aircraft and a special surface network over an island with physical features that satisfy approximately the model assumptions. Panoramic cloud photographs and time-lapse movies of the clouds were also taken. The observations show that evaporational cooling of the environment has an important, influence on the behavior of perturbations induced by the heated island.