Q COSTARICA — The national weather service, the Instituto Meteorológico Nacional (IMN), confirms that the North Pacific and the Central Valley will begin to notice the decrease in rainfall starting on November 18.
Yes, tomorrow.
This is due to a shift in cold fronts that is expected to bring forward the dry season in Costa Rica.
The IMN confirmed that the early arrival of the first cold front altered atmospheric behavior and predicts it will accelerate the transition to the dry season.
According to IMN meteorologist Daniel Poleo, the observed variation in the cold fronts for November will cause a gradual reduction in humidity in the northern and central regions of the country.
“There has been a significant change in the configuration of the cold fronts for the month of November,” Poleo stated.
“This modifies the start of the dry season in some areas. In the North Pacific and the Central Valley, the transition will be normal, occurring around the second half of November,” he added.
From Delayed to Normal Start
At the beginning of October, the IMN warned that the end of the rainy season would be delayed by at least a week, with rains potentially extending into December.
However, the new scenario presents a different picture.
According to Poleo, the arrival of the first cold front and the change in wind direction gradually reduced humidity, allowing the transition to return to the usual schedule.
“The fact that we have an early front favors a decrease in rainy conditions in some areas of the Pacific. The dry season will still be delayed in the South Pacific and the Central Pacific, but in the North Pacific and the Central Valley, we will have a normal start,” he added.
The meteorologist also noted that updates are part of the natural forecasting process and respond to normal climate variations.
“Climatic conditions vary from one period to another, which is why updates are made. Forecasts become much more precise as the predicted period approaches,” he pointed out.
Regional Transition
The new analysis from the IMN indicates that the North Pacific and the Central Valley will begin to experience a decrease in rainfall starting November 18, when the transition to the dry season will solidify.
In contrast, the Central Pacific and the South Pacific will continue to experience intermittent rainfall due to the influence of the Intertropical Convergence Zone (ITCZ), although with a downward trend as the weeks progress.
Poleo explained that, although the current cold front over the Caribbean Sea is not intense, it will be sufficient to mark the change in atmospheric patterns.
“This first cold front isn’t very strong, but it helps to reduce rainfall and favors the shift toward drier conditions,” he emphasized.
Meanwhile, the Caribbean slope and the Northeastern Zone do not have a defined dry season like the Pacific and the Central Valley, as they are affected by moisture from the Atlantic and the cold front systems typical of the Northern Hemisphere winter. Weekly
Forecast
The IMN forecast, valid from November 4 to December 1, summarizes the expected weather patterns:
- November 3-10: Heavy rains in the South Pacific due to the proximity of the Intertropical Convergence Zone (ITCZ) and windy conditions in the Caribbean. The rest of the country will experience typical seasonal rainfall.
- November 11-17: Decreased rainfall throughout the Pacific region and the beginning of the transition to the dry season.
- November 18-24: Establishment of the dry season in the North Pacific, Central Pacific, and Central Valley; the Caribbean will remain dry.
- November 25-December 1: Stable weather pattern with predominantly dry conditions across most of the country, except for isolated showers in the South Pacific.
The weather forecast for today, Monday, November 17, 2025:
Weak trade winds will persist throughout Monday, along with a drier air mass that will create a more stable atmosphere. However, isolated showers and thunderstorms are still possible during the afternoon in parts of the Central and South Pacific slopes.
On Monday afternoon, cloud cover will be partly cloudy across most of the country, with the possibility of overcast conditions and isolated showers and thunderstorms in the Central and South Pacific.
Showers or rain with occasional thunderstorms are possible in the mountains of the southern Northern Zone and north and west of the Central Valley. No precipitation is expected in the North Pacific and Caribbean, where mostly clear skies will prevail throughout the day.
Click here for your daily weather forecast from the IMN.