Original: Sometimes, a surge of dry air called the Saharan Air Layer (SAL) follows a tropical wave, leaving cloudless skies, as convection is capped by the dry layer inversion.
Simplified: Periodically, a surge of intensely dry air known as the Saharan Air Layer (SAL) is entrained behind a tropical wave, resulting in cloudless or nearly cloudless skies as convection is limited by the dry layer inversion.