Saharan Air Layer dust reaches the Lesser Antilles, Puerto Rico and the Gulf of MexicoThe major Saharan Air Layer dust outbreak (previously discussed here and here) continued its westward progression — and on 21 June 2020, GOES-16 (GOES-East) Split Window Difference (10.3 µm – 12.3 µm) and Dust RGB images (above) showed signatures of the dust (shades of tan to light brown in Split Window Difference, and shades of magenta in Dust RGB images) as it moved over the Lesser Antilles, the eastern Caribbean Sea and Puerto Rico. Surface reports at Port of Spain, Trinidad and Tobago (plot | data) indicated a drop in visibility below 1/2 mile for several hours, until some of the airborne dust was scavenged by convective precipitation; farther to the north, dust restricted the visibility to 3 miles at Barbados (plot | data). At San Juan, Puerto Rico (plot | data) the surface visibility only dropped to 7 miles, as most of dust remained aloft.
GOES-16 True Color RGB images created using Geo2Grid (below) showed the characteristic tan hues of the dust plume during daylight hours (1000-2200 UTC).
===== 22 June Update =====On 22 June, GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Aerosol Optical Depth (AOD) images (above) showed that the SAL dust had continued moving west, overspreading Puerto Rico, Hispaniola and much of the Caribbean Sea. Widespread AOD values of 1.0 to 1.8 were seen across that region.
A closer look at GOES-16 Split Window Difference and AOD images centered over Puerto Rico (below) revealed that the surface visibility was reduced to 3 miles at two sites in eastern Puerto Rico — and an AOD value of 2.0 was noted just south of San Juan TJSJ at 2201 UTC. The visibility was further reduced to 2-3 miles at nearby islands.
The visibility in San Juan, PR, was 3 miles for a while today due to Sahara Desert dust. Looking at the Local Climatological Data (LCD) files from the San Juan airport, there are no cases of sub–4 mile visibility since the early 1950s due to Haze in the summer months.
— Brian Brettschneider (@Climatologist49) June 23, 2020
GOES-16 True Color RGB images (below) depicted the thick plume of dust. A 9-day animation of a GOES-16 Split Window Difference “Saharan Air Layer product” covering the period 13-22 June 2020 (below) displayed the westward progress of the SAL plume (darker red to shades of white) across the Atlantic Ocean.
===== 24 June Update =====A 17-day animation of GOES-16 True Color RGB (daytime) and Dust RGB (nighttime) images during the period from 08-24 June (above) showed that (1) the primary strong SAL dust plume eventually reached the Gulf of Mexico on 24 June, (2) a second SAL dust plume emerged off the northwest coast of Africa on 22-23 June, and (3) the Dust RGB only exhibited a strong signature (brighter shades of magenta) for the most highly-concentrated areas of dust as they began to move westward off the coast of Africa — once the dust became more diffuse over the middle Atlantic, it lost a recognizable signature in the Dust RGB (while still retaining a good daytime signature in the True Color RGB).
A 12-day animation of GOES-16 Split Window Difference “Saharan Air Layer product” covering the period 13-24 June (below) also displayed the primary SAL plume reaching the Gulf of Mexico on 24 June, in addition to the secondary SAL plume emerging on 22-23 June.