Q COSTA RICA — Costa Rica’s 2026 rainy season is expected to begin withdrawing during the first days of November, though the transition will vary considerably by region.
According to the national weather service, the Instituto Meteorológico Nacional (IMN), the country could experience drier-than-usual conditions before the traditional dates associated with the end of the rainy season.
The change will begin in the North Pacific, including Guanacaste, which is forecast to be the first region to settle into the dry season. The Central Valley and the Central and South Pacific will follow several weeks later, with rainfall likely to continue intermittently through much of November.
Daniel Poleo of the IMN’s Climatology Unit said the transition is not necessarily expected to occur earlier than normal on the calendar. The difference, he explained, is that the shift could be noticeably drier than usual.
“We are expecting it to fall within the normal dates, but the transition could be dry,” Poleo said, according to the report.
North Pacific likely to enter the dry season first
The reduction in rainfall was expected to become more apparent during the second half of October. Between October 26 and November 1, the IMN forecast a particularly dry period in the North Pacific, Central Pacific and Central Valley, while other parts of the country were also expected to record rainfall below historical averages.
During the week of November 2–8, the dry pattern was projected to extend across the country. That development would support the establishment of the dry season in the North Pacific, where communities could see a sustained reduction in rainfall at the beginning of November.
The Central Valley and South Pacific, by contrast, are likely to experience a slower transition. Rainfall could persist across those regions for a significant part of November before declining more consistently.
The expected change will not necessarily mean that storms disappear. Rather, residents may notice fewer rainy days and longer intervals without precipitation. The IMN cautioned that short, intense downpours could continue even as monthly rainfall totals remain below normal.
October rainfall already showing a marked deficit
The shift comes after an unusually dry October in several areas. Weather stations near San José airport in Alajuela recorded a rainfall deficit of nearly 80%, despite October normally being one of Costa Rica’s wettest months.
The IMN’s October 16 climate update projected rainfall declines of up to 60% in the Central Pacific and northern Caribbean by the end of the month. Other regions were expected to see reductions of roughly 40%.
Those figures do not mean that every location remained dry. Much of the country recorded more than 100 millimeters of rain during the first 11 days of October, excluding the Caribbean.
The issue was the uneven distribution of that rainfall: some communities received heavy rain over a few hours, while nearby areas went several days without precipitation.
In Guanacaste, some locations experienced six or seven consecutive dry days. Certain parts of the Central Pacific went even longer without significant rain. The South Pacific also recorded totals below expectations.
Why heavy storms can coexist with dry conditions
The apparent contradiction—intense storms alongside a monthly rainfall deficit—is central to understanding this year’s transition.
According to the IMN explanation, warming associated with El Niño can increase evaporation and contribute to the development of cumulonimbus clouds. These clouds can produce very intense rainfall over short periods.
That pattern can lead to flooding in one community while neighboring areas remain unusually dry. A single storm may cause localized damage, but it does not necessarily erase a broader rainfall deficit accumulated over several weeks.
Recent heavy rain in parts of Heredia and Escazú illustrated that contrast. Other sections of the Central Valley received considerably less precipitation during the same period.
The decline in average rainfall also does not eliminate the risk of flooding. Dry intervals and concentrated storms can occur during the same phase of the season, meaning that reduced rainfall should not be interpreted as a complete end to hazardous weather.
Caribbean and Northern Zone face a different seasonal pattern
The Caribbean and Northern Zone do not have a fixed start date for the dry season in the same way that the Pacific regions and Central Valley do. Their rainfall patterns differ, and precipitation can continue throughout the year.
Even so, the IMN’s outlook for November 2026 through January 2027 projected rainfall roughly 30% below normal in both regions.
The forecast also distinguishes between areas experiencing meteorological drought. The Western Northern Zone, including Guatuso, Los Chiles and Upala, had moved out of drought conditions after receiving substantial rainfall in July and August—months that typically contribute significant precipitation there.
The Pacific regions and Central Valley, on the other hand, continued to show signs of meteorological drought and were expected to maintain conditions more typical of the dry season during the following three months.
Analysis: a dry-season transition, not a clean break
The most important point in the IMN outlook is that Costa Rica will not switch from rain to dryness all at once. The transition will be regional, uneven, and marked by sharp contrasts.
Guanacaste and the North Pacific are likely to feel the change first, while the Central Valley and South Pacific may continue to receive sporadic rainfall into November. The Caribbean and Northern Zone will follow a different rhythm altogether, with no single date defining the end of their rainy period.
The early signs are already visible: extended dry intervals, below-average rainfall totals and a widening gap between communities that experience intense storms and those that receive almost none. For agriculture, water management and disaster planning, that unevenness may matter more than the national average.
Residents should therefore avoid treating the beginning of November as a guarantee of uninterrupted dry weather. A longer dry spell may arrive, yet isolated storms can still produce flash flooding, especially where rainfall falls in concentrated bursts.
The 2026 transition is best understood as a gradual retreat of the rainy season. The first clear shift is expected in the North Pacific in early November, while other regions will move toward drier conditions at different speeds.