Tropical Wave 51, Trough To Sheild T&T From Significant Saharan Dust Surge

As Hurricane Sam pulls northward, a mild surge of Saharan Dust is moving Trinidad and Tobago, as forecast, with a more significant surge arriving north of the country this weekend. Rainfall associated with a Tropical Wave 51 and a trough is also forecast to affect T&T from Saturday, tempering the air quality impacts across the country.

Higher concentrations of dust are forecast to remain north of Trinidad and Tobago through the next ten days.

Over the last 24 hours, air quality has been good with visibility near and above 10 kilometers across Trinidad and Tobago. The Environmental Management Agency (EMA) air quality monitoring stations are recording AQI values at levels that are good across the country. These measurements are based on PM2.5 (particulates the size of 2.5 micrometers and smaller, usually associated with increases in Saharan Dust, vehicle exhaust, and smoke) and PM10 particulates.

The Saharan Dust Forecast

Tropical cyclones have continued to keep Saharan Dust concentrations at bay across the Lesser Antilles, with only minimal concentrations moving across the island chain over the last few weeks.

Model guidance suggests a mild surge is forecast to continue moving across T&T through Sunday 3rd October 2021. However, as mentioned above, rainfall is also set to increase from this weekend into next week as a mix of Tropical Wave 51 and a trough affects the country.

The trough system is forecast to “scrub” the air, resulting in good air quality from mid-Sunday through Monday, with mild Saharan Dust lingering into the weekend.

Generally, air quality levels are forecast to remain good levels, only becoming moderate during high-traffic periods. Outside of rainfall, visibility is forecast to remain at or above 10 kilometers.

12Z 30th September 2021, NASA GEOS-5 Dust Extinction Model Monitoring Tropical Atlantic Dust Aerosol Optical Depth showing Saharan Dust.

What does this mean for you?

Over the next 10 days, air quality is forecast to remain at mostly good levels. However, during high traffic periods, particularly between 6:00 AM and 9:00 AM, and again during 3:00 PM through 6:30 PM, air quality may dip to moderate levels in localized areas.

For sensitive groups, such as children, the elderly, and persons who suffer from respiratory ailments and allergies, you may need to avoid prolonged exertion outdoors during these high traffic periods.

We’re in a period where the ITCZ, tropical cyclones, and tropical waves may shield Trinidad and Tobago from significant dust events. While tropical waves play a notable role in moving dust across the Atlantic and the Eastern Caribbean, these periodic tropical waves also improve air quality.

The concentration of the dust that follows the wave depends on the strength of the wave as it moves off the West African Coast. This is because of stronger thunderstorms across Central Africa. As strong winds move downward and outward from these thunderstorms, the wind kicks up dust as it moves across parts of the Saharan Desert and transports it into the upper atmosphere. This “plume” of dust follows the axis of the wave as it progresses westward into the Atlantic.

Dust that makes it into the upper levels of the atmosphere can then get transported across the Atlantic Ocean. The plumes of dust eventually affect the Eastern Caribbean.

Larger, more concentrated plumes of dust begin to occur in April and continue through November.

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