Q COSTARICA — The subtropical jet stream, a high-altitude air current, is acting as a barrier, preventing cold fronts from descending into Central America and the Caribbean.
This phenomenon helps explain why several cold air systems have failed to directly impact Costa Rica in recent months.
This was explained by Rodrigo Castillo, a researcher at the Center for Geophysical Research and the Laboratory of Atmospheric Engineering and Physics at the University of Costa Rica (UCR).
This atmospheric current has intensified over Mexico.
“Furthermore, the subtropical jet stream is beginning to strengthen and acts as a block, preventing potential cold fronts from descending to tropical latitudes or even entering the Caribbean basin,” Castillo explained.
According to the expert, the strengthening of the jet stream began in March and is mainly due to changes associated with the transition of the La Niña phenomenon to a neutral phase.
“During La Niña, the cooling of the equatorial Pacific waters modifies tropical atmospheric circulation and can alter the distribution of rainfall and temperatures in different regions of the planet, including Central America,” he explained.
Effects
According to the expert, the subtropical jet stream is a very strong air current that, when it intensifies, can:
- Modify the trajectory of weather systems
- Limit the movement of cold air masses toward regions closer to the tropics
In the case of Central America, its strengthening can prevent cold fronts from the Northern Hemisphere from advancing.
This means that, although cold fronts will continue to occur, their direct influence on the country may be less.
Cold Air Outbreaks
According to the national weather service, the Instituto Meteorológico Nacional (IMN), the 2025-2026 cold air outbreak season is progressing as expected.
The seasonal forecast indicates that the following values are typically recorded:
- 22 cold air outbreaks between October and April
- 16 outbreaks between November and February
To date, 15 cold air outbreaks have been recorded in the Caribbean, but only two cold fronts have directly affected the national territory.
According to Karina Hernández, from the IMN’s Climatology Unit, not all of these systems directly impact the country.
“Cold air outbreaks are masses of cold air that move toward the Caribbean, but we only refer to a cold front when that system directly reaches the national territory,” she explained.
“Normally one or two cold fronts arrive in Costa Rica per season, so the two events recorded this year (one in January and another in February) are within expectations,” Hernández added.
Wind and Cold Weather
Although the impact of these weather systems has been limited in terms of rainfall, changes in the perceived temperature were noticeable.
This occurred during the first two months of 2026, when historically low temperatures were even recorded during the dry season.
“When these events occur, the most noticeable effects in the country are usually stronger winds and a drop in temperatures, especially in the Central Valley and mountainous regions,” noted the expert from the National Meteorological Institute (IMN).
“In the Caribbean, on the other hand, rainfall associated with the passage of these cold air masses is more common,” added Hernández.
According to the IMN forecast, a cold front is possible in the coming months due to its late start.