 In July the trade winds south of the northward @-@ moving subtropical ridge expand northwestward into Florida . On occasion , dust from the Sahara moving around the southern periphery of the ridge moves into the state , suppressing rainfall and changing the sky from a blue to a white appearance and leads to an increase in red sunsets . Its presence negatively impacts air quality across the Southeastern United States during the summer , by adding to the count of airborne particulates . This is in sharp contrast to the normally clean air over Florida and the southeastern USA , which on average is the cleanest air in the USA . Over 50 % of the African dust that reaches the United States affects Florida . Since 1970 , dust outbreaks have worsened due to periods of drought in Africa . There is a large variability in the dust transport to the Caribbean and Florida from year to year . Dust events are possibly linked to a decline in the health of coral reefs across the Caribbean and Florida , primarily since the 1970s . 
