A new push of Saharan dust is expected to spread across Costa Rica this week, bringing hazy skies, reduced visibility and poorer air quality, with Thursday and Friday forecast to be the most difficult days. The dust will affect nearly all of Costa Rica, although higher concentrations are expected in Alajuela, western parts of the Central Valley and some areas of Cartago.
Residents may notice a pale or milky appearance in the sky known as calima, caused by fine particles suspended in the atmosphere. Visibility over mountains and other distant landmarks could also become noticeably worse. The conditions are expected to become more apparent beginning Wednesday before reaching their strongest point on Thursday, July 30, and Friday, July 31. Air quality should begin improving Saturday as the dust moves north toward other parts of Central America and Mexico.
People with asthma, allergies and other respiratory conditions face the greatest risk. Children and older adults should also reduce the amount of time they spend outdoors during the highest concentrations. The warning extends beyond people with existing health problems. Residents in generally good health are being advised to avoid long periods of strenuous outdoor activity on Thursday and Friday, including extended runs, cycling or outdoor exercise lasting several hours.
Fine particles carried within the dust can enter the respiratory system and cause irritation. Possible symptoms include coughing, itchy eyes or throat, headaches, chest discomfort, breathing difficulty and worsening asthma or allergy attacks. People who must remain outdoors should limit their exposure and consider wearing a well-fitting mask, particularly if they have respiratory problems. Anyone who develops discomfort while exercising should stop the activity and move indoors.
The Saharan dust originated over North Africa and traveled thousands of kilometers across the Atlantic Ocean and Caribbean Sea before reaching Central America. These events are common during the middle of the year, when strong trade winds carry dry air and mineral particles westward.
The approaching dust will combine with stronger winds, locally raised soil particles, pollen and smoke still present from regional burning. Together, those elements can increase the amount of material suspended in the air even when the Saharan particles are not clearly visible. Lower rainfall will make the situation more noticeable. Rain normally helps remove dust and other particles from the atmosphere, but Costa Rica is expecting a significant reduction in precipitation over the next several days.
The dry air associated with Saharan dust can also limit the development of rain clouds, allowing particles to remain suspended longer. The episode is not expected to produce dangerously polluted conditions across the country. However, prolonged exposure could cause problems for sensitive people and make outdoor activity uncomfortable even for otherwise healthy residents.
You may also encounter hazier views from mountain overlooks, volcanoes and higher-elevation destinations. Flights are not currently expected to face major disruptions, although distant visibility could be reduced. Conditions are forecast to improve considerably over the weekend as the main concentration of dust moves away from Costa Rica.
