How the Saharan air layer (SAL) affects tropical cyclone intensity in the North Atlantic Ocean is an issue in debate. A composite study of 274 cases from 37 named tropical cyclones that formed during the period 2005–2007 is conducted using AIRS relative humidity between 600–700 hPa. Typically the dry SAL air is first observed within 1000 km north of the tropical cyclone center and then intrudes southward and towards the inner region of tropical cyclones along the cyclonic flow. This study provides evidence that the SAL can affect tropical cyclone intensity in both favorably and unfavorably manners by intensifying tropical cyclones when it is first found mostly in the northwest quadrant and then weakening tropical cyclones when its dry air intrudes within 360 km of the tropical cyclone center, mostly in the southwest and southeast quadrants. It appears that the SAL is favorable for the initial development of tropical cyclones but unfavorable for their subsequent intensification.