According the US National Weather Service San Juan, there will be Saharan dust in the region until tomorrow.
Saharan Dust: How Does it Impact Atlantic Storms?
The Saharan Air Layer, or known more commonly as Saharan Dust, is a layer of tiny aerosols like sand, dirt, and dust that occasionally push from east to west across the tropical Atlantic Ocean during hurricane season. These aerosols originate over the very hot and dry deserts of Africa, like the Saharan Desert, and sometimes get picked up by African Easterly Waves which push westward from Africa into the Atlantic Ocean.
The Saharan Air Layer is a well-mixed dry pocket of air that usually resides between 5,000 and 15,000 feet above sea level. Since one of the key ingredients for tropical cyclone development is a deep feed of moisture, Saharan Dust often acts to inhibit tropical development. Research suggests that there are three primary reasons Saharan Dust has a negative impact on tropical development:
1) A surge in the mid-level African Easterly Jet increases the vertical wind shear.
2) The inclusion, or drawing in, of dry air into a tropical system
3) An enhanced trade wind inversion which acts to stabilizes the atmosphere. A stable atmosphere will make it more difficult for deep convection to develop.
Once a pocket of Saharan Dust begins moving westward over the Atlantic Ocean, it is relatively easy to track by using certain infrared satellite products. The algorithm in some infrared products is sensitive to dry, dusty air and, therefore, can track when pockets of this kind of air move from place to place.
Many factors go into forecasting the track and strength of a tropical system. Knowing whether or not a tropical cyclone will have Saharan Dust in its vicinity is one factor that can determine the cyclone’s intensity. (source: AccuWeather)