October is shaping up to be a wetter-than-normal month in much of Costa Rica, according to the National Meteorological Institute (IMN). The Pacific coast, the Central Valley, Guatuso, Los Chiles, and Upala could see up to 15% more rainfall than average.
In contrast, the Caribbean will maintain a drier pattern, with a deficit close to 10%, in addition to slightly warmer temperatures. “In the Caribbean, deficit conditions of up to 10% are expected, with slightly warmer temperatures, up to half a degree above normal,” explained Karina Hernández, IMN climatologist.
On the other hand, the IMN will not publish the approximate dates for the end of the rainy season until mid-October. However, Hernández stated that they expect the onset of the cold snap season, from November to May, to be delayed, which could cause the rainy pattern to persist longer in Costa Rica.
According to the specialist, the scenario will favor a later-than-usual end to the rainy season. “It is likely that the end of the rainy season will be delayed,” she stated.
La Niña and the Bipole
On the other hand, although La Niña is under surveillance, the IMN estimates that 2025 will end in a neutral phase. Hernández noted that for it to be declared, at least three consecutive rolling quarters are required, which is approximately five months with cold ocean temperatures below -0.5°C and the corresponding atmospheric reaction. So far, it has been in that state for one month.
“What is expected is that the remainder of 2025 will end as a neutral phase; La Niña has not yet developed,” he stated. The current oceanic scenario creates a climate bipole: the equatorial Pacific remains neutral-cold while the Caribbean Sea remains warmer than normal, although not at record levels as in 2023 and 2024.
“Right now we don’t have La Niña, but we have a cold neutral phase with a Caribbean Sea that remains warm. So, associated with that, the end of the rainy season is even expected to be slightly delayed. Rainy scenarios are forecast for October and November on the Pacific side, and that all goes hand in hand. So, we won’t have La Niña, but we will have a greater contribution of rainfall,” he explained.
Weekly Forecast
The IMN extended forecast confirms that rainfall will be above normal in the Pacific and Central Valley for much of October, while the Caribbean will remain drier.
September 29 to October 5: The entire Pacific region will experience more than normal rainfall, with weekly amounts of 90 to 120 mm. The Caribbean region will experience less rain, and the rest of the country will experience normal rainfall.
October 5 to 12: The Pacific region will experience normal rainfall for the season. The Caribbean region will maintain a less rainy pattern.
October 13 to 19: The Pacific region and Central Valley will experience above-average rainfall. The Caribbean region will return to a normal pattern with little precipitation.
October 20 to 26: The Pacific region and Central Valley will experience more rain than normal. The Caribbean region will again experience less rain.
“October will be more consistently rainy compared to September, which is already one of the rainiest months of the year,” Hernández emphasized.
Meteorological Drought
The Mexican National Meteorological Institute (IMN) also clarified that there is currently no meteorological drought in Costa Rica. However, surveillance remains ongoing in the Caribbean, Limón, Valle de la Estrella, and northern Cartago, where specific deficits have been observed over the past four months that could evolve if sustained.
“There is currently no meteorological drought, but we are monitoring the Caribbean because it has shown deficits in recent months,” the climatologist indicated. To officially declare this phenomenon, three rolling quarters of precipitation deficits are required, a condition that has not yet been met.
“A year ago, we had a significant meteorological drought in the Caribbean. It lasted a long time, leading to problems with the electricity supply during the dry season, when we cannot rely as much on hydroelectric plants. Hence the importance of monitoring the potential for rainfall in the coming months,” she emphasized.
Rainfall from normal to surplus
So far, the annual balance shows that Costa Rica has had more rainfall than usual and within the normal range in some regions, despite variations and specific months with deficits.
“The first eight months of 2025 have seen more rainfall than usual in Costa Rica,” Hernández stated. He explained that, as of July, surpluses were recorded in almost the entire country, with the exception of the Caribbean. Although August showed a deficit and reduced accumulated rainfall, the annual total remains above the historical average.
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