Q COSTARICA — Costa Rica has experienced eight episodes of Saharan dust this year. This is a higher figure than the frequency observed in previous years, according to the national weather service, the Instituto Meteorológico Nacional (IMN).
Meteorologist Daniel Poleo explained that this does not mean that there has been a higher concentration of dust in general, but rather that the arrivals have been more constant.
Furthermore, so far this year, the expert highlights episodes of Saharan dust with high values.
“These masses are continuous; on at least eight occasions we have had high records; for example, one of them lasted about five days,” the expert explained.
“So in general, this year we have had more frequent arrivals of Saharan dust to Central America. However, this does not mean that there has been a greater amount of dust in general; in other years there was more concentration, but in one or two events,” Poleo explained.
Why more dust?
Poleo explained that this situation is due to a series of factors, such as:
- Increased trade winds, especially in the Caribbean Sea.
- High-pressure systems in the Atlantic are strong enough to move dust masses from Africa to Central America.
Less Rain and Weaker Waves
Poleo explained that this dynamic has had direct consequences on the climate.
“With this large amount of Saharan dust arriving, one of the consequences was a more intense and much more widespread heat wave, drier conditions compared to normal in some areas, and even an impact on air quality,” he mentioned.
Although the heat wave had some breaks with days of heavy rain, it began on July 7 and for the second half of the month, it remains less rainy due to the presence of dry masses.
He also explained that the Saharan dust phenomenon has an effect on tropical waves.
“The waves tend to arrive with less intensity, and when they do, they generate less precipitation. What favors the dust is the less active Intertropical Convergence Zone,” he explained.
Regarding a new mass observed on Monday in satellite images, Poleo indicated that it will not directly hit Costa Rica.
“That mass will be carried northward by Hurricane Erin; at least until Saturday, we will have little impact from the Saharan dust,” he confirmed.
Coming Weeks
According to the IMN forecast, the Intertropical Convergence Zone (ITCZ) is expected to remain close to Costa Rica this week, along with weak trade winds.
“Under these conditions, local factors such as daytime warming and sea breezes, combined with the ITCZ, will favor the formation of showers and thunderstorms during the afternoons this week,” the Meteorological Institute predicts.
While the last week of August will continue with less rain than usual.
“On the other hand, a significant change in rainfall is expected starting in the first week of September, with the entire Pacific and Central Valley expected to experience more rain,” experts predict.
The weekly forecast is:
- August 25-31: This last week of August, the Caribbean and Northern Zone will tend to experience less rain than normal for this season. The Pacific and Central Valley will experience afternoon rainfall typical of the season, with weekly rainfall in the Pacific between 30 and 120 mm, the Caribbean and Northern Zone between 20 and 80 mm, and the Central Valley between 10 and 55 mm.
- September 1-7: Rainier-than-normal conditions are expected in the Pacific and Central Valley, due to weaker trade winds and increased humidity, particularly due to the proximity of the Intertropical Convergence Zone. Meanwhile, the Caribbean and Northern Zone will experience less rainfall than normal.
- September 8-14: Wetter-than-normal conditions are expected to continue in the Pacific, due to weak trade winds and increased humidity. The Caribbean and Northern Zone will experience less rainfall than normal, while the rest of the country will experience normal seasonal rainfall (higher probability of cyclones in the Atlantic basin).
- September 15-21: This week, the entire Pacific, Central Valley, and Northern Zone will experience more than normal rainfall for this season. On the other hand, the Caribbean will experience less than normal rainfall, while the rest of the country will experience normal rainfall for this season.
The IMN weather forecast for today, Tuesday, August 19, 2025:
The typical pattern for the rainy season will be present today. Local factors such as warm morning temperatures and sea breezes will facilitate cloud development, leading to rain and thunderstorms in the afternoon, which may extend into the early evening.
The regions most likely to experience rain and thunderstorms are the Central Pacific, South Pacific, Nicoya Peninsula, Tempisque Valley and its surroundings, as well as the Central Valley, the North Zone, and the mountainous areas of the Caribbean.
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