Saharan Dust in the Virgin Islands

Is there Saharan dust in the Virgin Islands today?

No. Copernicus's forecast has no Saharan dust to speak of over the Virgin Islands through October 12: under 10 µg/m³ at the surface every day. Dust season at the islands peaks from late June to mid-August (NOAA).

The Copernicus CAMS forecast through the Open-Meteo Air Quality API, read again every hour. Copernicus’s cells are about 40 km across: St. Thomas, St. John, Tortola and Jost Van Dyke share one. A model reading, not a measurement on the ground. In Florida this week: Miami clear, Clearwater clear.

The 2026 dust season at the islands

From May to early October 2026 Copernicus's model put 42 days of noticeable dust over St. Thomas, St. John, Tortola and Jost Van Dyke (a daily mean of 25 µg/m³ or more at the surface), 13 of them 50 or more. July was the dustiest month. The single dustiest day was September 12, when the model's PM10 reached 180 µg/m³: the only day since August 2022 over the EPA's 24-hour standard of 150 µg/m³, in the range the EPA's Air Quality Index calls unhealthy for sensitive groups.

Daily means of the dust at the surface over St. Thomas, St. John, Tortola and Jost Van Dyke (one Copernicus CAMS cell). A model reading, not a measurement on the ground: the USVI’s own air monitors are not public in real time.

The September 2026 plume, from Africa to the islands

On September 7 NASA's AERONET sun photometer on Sal, Cape Verde, measured an aerosol optical depth (AOD) of 1.10. NASA calls a value under 0.1 crystal clear and 1 very hazy. In NASA's GEOS-FP model the plume's front went from 28° W on September 5 to past the islands at 66° W on September 10: 4,000 km in 5.0 days, about 33 km an hour, close to the 1,000 km a day found for the great plume of June 2020 (Yu and others, 2021).

On September 12 the photometer at Cape San Juan, on Puerto Rico's north-east tip, 4,500 km west of Sal, measured AOD 0.62 with an Ångström exponent of 0.09. A low exponent means coarse particles, which over the Caribbean in summer is desert dust. That day Copernicus put 224 µg/m³ of dust in the air over the islands. The table follows the front in NASA's model, once a day.

Every summer since 2023

Copernicus's daily record for the islands, as served by Open-Meteo, goes back to August 2022, and every summer since has brought dust; the counts below use the same thresholds. Measured records go back much further. On Barbados the University of Miami has sampled the trade winds for dust since 1965: the dust rises and falls with drought in the Sahel, and in 1983 and 1984 ran four times its pre-drought levels (Prospero and Nees, 1986; Prospero and Lamb, 2003). The record day there, 272 µg/m³, was April 9, 1994 (Zuidema and others, 2019).

What the sun photometers measured

NASA's AERONET network measures the haze directly, with sun photometers that look at the sun through the day. There is none in the Virgin Islands; the nearest is at Cape San Juan, on Puerto Rico's north-east tip, 73 km west of St. Thomas. The Ångström exponent tells dust from smoke and pollution: dust grains are coarse, so their exponent is low. This page calls a day desert dust when it is under 0.4. These are Level 1.5 data (cloud-screened, not yet given NASA's final quality check).

How Saharan dust crosses the Atlantic

The dust is lifted from the Sahel and the western Sahara, often by the storms called haboobs (the June 2020 plume came mainly from Niger, Mali and Mauritania), and carried as high as 6 to 7 km in hot, dry air. At the African coast that air rides up over the cooler, moister trade winds and becomes the Saharan Air Layer: 1.5 to 6 km up, about half as moist as ordinary tropical air, with winds of 10 to 25 m/s inside it (NOAA AOML; Prospero and others, 2021).

In summer an outbreak leaves the coast every 3 to 5 days (NOAA AOML) and reaches the Caribbean about a week later (Prospero, 2006). This summer the dust over the islands followed the dust over Sal by about 3.8 days in Copernicus's model (the best-fitting lag; correlation 0.43). From NASA's CALIPSO lidar, about 182 million tonnes a year leave the coast at 15° W, 132 million reach 35° W and 43 million pass 75° W, west of the islands (Yu and others, 2015; uncertain by 45 to 70%).

Summer dust reaches the Caribbean and North America because the tropical rain belt moves north in summer; in winter and spring the dust goes to South America instead, where about 28 million tonnes a year fall on the Amazon (Yu and others, 2015).

What the dust means on the islands

The sky. On a dusty day it looks milky white, and the sunsets can glow orange (NOAA AOML), though heavy haze tends to mute them to pale yellows and pinks (NOAA Storm Prediction Center).

The weather. The dry, dusty air smothers clouds and showers, and some places have their hottest days of summer under it (NOAA AOML). Its dry air and strong winds can weaken tropical storms, but how much is debated: a NASA study found the layer "is not a determinant" of whether a storm strengthens (Braun, 2010), and what the dust itself does is "not yet clear" (NOAA AOML).

Health. Fine particles matter most for people with heart or lung disease, older adults and children (EPA). On heavy days the VI Department of Health advises them to stay indoors with their asthma plan and rescue inhaler at hand, and everyone to walk instead of run, wear a mask outdoors, and shower and change clothes after coming in. Studies in the Caribbean disagree on how much dust adds to asthma: links were found in Trinidad and Guadeloupe, a weak one in Grenada, none obvious in Barbados.

Alerts. In the USVI the Department of Planning and Natural Resources issues air-pollution alerts for Sahara dust; its 2025 network plan lists a PM2.5 monitor at Vendor's Plaza on St. Thomas, set up for daily reporting in dust storms, and a coarse-particle monitor at Bethlehem Village on St. Croix kept for dust episodes. On the EPA's Air Quality Index, a day's PM10 over 154 µg/m³ is unhealthy for sensitive groups and over 254 unhealthy.

The same dust in Florida

The same summers reach Florida, Texas and the Gulf coast (NOAA AOML). In July 2026 Copernicus put 62 µg/m³ of dust over Miami on July 12 and 86 over Clearwater on July 13; Miami's measured record, kept since 1974, peaks in July (Zuidema and others, 2019). On June 27, 2020 the great plume known as Godzilla pushed fine-particle levels at 62 of 150 monitors in the southern U.S. over the EPA's 24-hour standard (Yu and others, 2021).

How this map is made

The film's dust: NASA GEOS-FP dust aerosol optical depth at 550 nm (DUEXTTAU), 3-hourly time averages read every 6 hours from June 1 to October 7, 2026 (NCCS OPeNDAP, 0.5° × 0.625°), drawn as haze whose opacity rises with the depth. Between two model times the field is carried along by the model's own 700 hPa wind in the shader, so plumes move instead of cross-fading; the drifting grains follow the same wind. The Earth is NASA's Blue Marble Next Generation; the photographs are VIIRS true colour from NOAA-20 (September 9) and Suomi NPP (September 11).

The plume's front: for each model time, the westernmost longitude between 13° and 23° N where the dust optical depth exceeds 0.45, following the September plume from Africa to past the islands.

Dust at the islands, Florida, Barbados and Cape Verde: the Copernicus CAMS global model (about 40 km cells) through the Open-Meteo Air Quality API, hourly surface dust and PM10 averaged into daily means; the record served there starts in August 2022. A day is dusty at 25 µg/m³ or more and very dusty at 50 or more (thresholds chosen for this page). St. Thomas, St. John, Tortola and Jost Van Dyke share one model cell. The lag between Sal and the islands is the shift that best correlates the two daily series over the summer (3.8 days, r = 0.43).

The measurements: NASA AERONET Version 3 Level 1.5 daily means of aerosol optical depth at 500 nm and the 440–870 nm Ångström exponent, for Sal (Capo_Verde), Ragged Point (Barbados), Cape San Juan and La Parguera (Puerto Rico).

1. NASA GEOS-FP (GMAO), dust aerosol optical depth and 700 hPa wind
2. Copernicus Atmosphere Monitoring Service (CAMS) global forecast
3. Open-Meteo Air Quality API (CAMS)
4. NASA AERONET sun photometers (Version 3, Level 1.5)
5. NASA GIBS / Worldview (VIIRS true colour, Blue Marble)
6. NOAA AOML, the Saharan Air Layer
7. NOAA AOML Hurricane FAQ A17, the Saharan Air Layer and hurricanes
8. Prospero (2006), Saharan dust impacts and climate change, Oceanography 19(2)
9. Yu and others (2015), the trans-Atlantic dust flux from CALIPSO, Remote Sensing of Environment 159
10. Yu and others (2015), the fertilizing role of African dust in the Amazon, GRL 42
11. Yu and others (2021), the June 2020 trans-Atlantic dust event, ACP 21
12. Mayol-Bracero, Prospero and others (2025), African dust in the Greater Caribbean, BAMS 106
13. Zuidema and others (2019), the Barbados and Miami dust records, BAMS 100
14. Prospero and Nees (1986), Nature 320
15. Braun (2010), Reevaluating the role of the Saharan Air Layer in Atlantic tropical cyclogenesis, Monthly Weather Review 138
16. EPA, particle pollution standards and the Air Quality Index
17. Virgin Islands Department of Health, Saharan dust advice
18. USVI DPNR, Air Monitoring Annual Network Plan 2025
19. NASA Earth Observatory, aerosol optical depth