Saharan Dust outbreak across San Fernando on Sunday morning, bringing orange skies to the area with dense, Saharan Dust.
An unprecedented event. This Saharan Dust Outbreak is nothing Trinidad and Tobago has experienced in recent history. Initial peak concentrations occurred across Tobago at 4:00 AM Sunday, reducing air quality levels to hazardous for the first time in recorded history due to Saharan Dust. Peak concentrations occurred across Trinidad at 9:00 AM Sunday, with air quality levels between unhealthy to very unhealthy.
The Journey of The Saharan Dust Outbreak
This particular plume of dust moved off the coast of Africa on June 10th into June 11th, behind Tropical Wave 10.
We’re in a period where the ITCZ and tropical waves shield Trinidad and Tobago from the Saharan Dust events. While tropical waves play a notable role in moving dust across the Atlantic and the Eastern Caribbean, these frequent tropical waves also aid in improving 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.
Larger, more concentrated plumes of Saharan dust begin to occur in April and continue through November.
This surge of Saharan Dust also coincided with a trade wind surge. Trade wind surges are increases in the surface wind speed, which come from the general direction of the trade winds and are caused by any feature which causes a tightening in the pressure gradient. This could include the strengthening of a nearby high-pressure system or the passage of a low-pressure system. This is presently moving across the Southern Windwards, with wind speeds peaking overnight across T&T. Gusts up to 70 KM/H possible, with sustained winds up to 50 KM/H.
A trade wind surge can cause an increase in wind convergence along the monsoon trough, which generally results in increased convection and the development of clouds and thunderstorms. This will also be the case as Tropical Wave 12 moves across the Southern Windwards overnight.
Overwhelming Model Support
Forecast models quickly picked up on the severity of the dust plume, with long-range modeling showing a significant plume of dust arriving across the Eastern Caribbean on Friday, with a more severe surge following Tropical Wave 11.
Our forecast called for unprecedented air quality levels across Trinidad and Tobago, with the air quality reaching very unhealthy (due to Saharan Dust) on Sunday into Monday. However, this surge of Saharan Dust exceeded the forecast particulate matter, which affects air quality, with initial peak PM10 concentrations at 530 µg/m3 across Tobago and 303 µg/m3 across Trinidad. Initial peak PM2.5 concentrations were 151 µg/m3 across Tobago and 108 µg/m3 across Trinidad.
PM2.5 are particulates the size of 2.5 micrometers and smaller, usually associated with increases in Saharan Dust, vehicle exhaust and smoke and PM10 particulates are the particles we use to track Saharan Dust air quality, though the overall air quality is also made up of carbon dioxide, ozone, sulfur dioxide, and nitrogen dioxide.
Why is this Saharan Dust Outbreak significant?
The air quality index: a hazardous air quality alert.
For the first time since the establishment of the Environmental Management Agency’s Ambient Air Quality Monitoring Stations, the air quality for particulate matter has reached “hazardous” for Tobago, and “very unhealthy” for Trinidad.
The air quality index: a very unhealthy air quality alert.
With air quality at very unhealthy levels, health alerts may be issued as everyone may experience more serious health effects. There will be a significant aggravation of heart or lung disease & premature mortality in persons with cardiopulmonary disease and the elderly. A significant increase in respiratory effects in the general population is expected.
With air quality at hazardous levels, health warnings of emergency conditions. The entire population is more likely to be affected. There will be a serious aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly. In addition, there will be a serious risk of respiratory effects in the general population.
This is particularly significant due to the established link between Saharan Dust events and increased mortality. One study in the Canary Islands, where severe dust events are common noted an “86% of in-hospital heart failure mortality cases occurred during Saharan dust episodes that resulted in PM10 > 50 µg/m3.” This particular dust event, initial peak PM10 concentrations at 530 µg/m3 across Tobago and 303 µg/m3 across Trinidad were recorded on Sunday.
For the first time since we’ve been monitoring Saharan Dust events across Trinidad and Tobago, visibility dropped to 700 meters across Trinidad and 4 kilometers across Tobago. This presents a real hazard for air traffic and mariners. Mariners should remain in port particularly if GPS is not on the vessel.
This plume of dust will continue its westward journey, heading across the Greater Antilles, Central America and the U.S. Gulf Coast this upcoming week, reducing visibility and air quality across the regions.
Presently, as of 2:00 PM Sunday 21st June 2020, air quality across Trinidad and Tobago are both at unhealthy levels. Further improvement is forecast over the next 12-24 hours as a weak tropical wave (Tropical Wave 12) moves across both islands. Increasing moisture will fuel showers mainly across Trinidad, improving air quality into mid-Monday.
As the wave moves west, another significant (but less severe) surge of dust is forecast to move in late Monday, with peak concentrations Monday night into Tuesday. Concentrations are forecast to slowly decrease across T&T into Thursday, with Tropical Wave 13 moving across the island, bringing elevated chances for showers and thunderstorms.
Looking past the 5-day forecast, longer-range modeling shows another moderate surge arriving across the region on Friday, lingering into the weekend, gradually improving into next week with mild to moderate concentrations persisting into the end of June.
Sensitive groups such as persons with respiratory ailments, children, the elderly and cardiopulmonary disease should take the necessary precautions on days where dust concentrations degrade air quality to moderate and beyond, as there is more Saharan Dust forecast.