October continues delivering classic rainy season conditions as the Intertropical Convergence Zone maintains its position over Costa Rica, generating the bulk of rainfall we’ll experience in the coming days. This week brings two tropical waves through the region, which are normal features of October weather that will enhance rainfall patterns.
Tropical Wave #39 arrives early Tuesday morning, intensifying rain across the country, particularly affecting the Caribbean, Northern Zone, and mountainous regions with overnight and morning precipitation. This represents a departure from the typical afternoon-focused pattern we’ve been in.
Tropical Wave #40 is currently being monitored by the US National Hurricane Center with a 90% probability of developing into a tropical depression by midweek (October 23-26). Current forecast models indicate its primary impacts would concentrate on Caribbean islands, with possible influence reaching Central America starting Wednesday. This could bring rainier conditions during the second half of the week, mainly across Pacific regions.
Important Context: Tropical waves are normal October weather features in Costa Rica. While TW#40’s potential development warrants monitoring, there’s a lot of uncertainty about its exact evolution and trajectory.
This week has started off with only moderate rainfall in many parts of Costa Rica. But heavy storms have caused localized flooding and landslides in the past weeks.
Soil Saturation Alert: Ground moisture levels remain high in Guanacaste, Nicoya Peninsula, Northern Zone, and throughout the South Pacific. These areas have increased vulnerability to flooding, landslides, and river overflow. Urban areas are a specific concern due to potential stormwater drainage issues.
Generally cloudy to overcast conditions dominate with possible rain moving inland from coastal areas. Starting Wednesday, the South Pacific coast may experience rainfall during early morning hours as TW#40’s potential influence begins affecting the country.
Tuesday morning deserves special attention as Tropical Wave #39 arrives, bringing enhanced overnight and morning precipitation to Limón province and surrounding areas including the Northern Zone and the Central Valley and Talamanca mountain ranges.
Cloudy skies blanket the nation with showers and thunderstorms throughout Pacific and Central Valley regions. The afternoon storm pattern intensifies during the week’s second half as TW#40’s possible influence increases atmospheric moisture and instability. Moderate rainfall develops across Northern Zone and Caribbean plains toward the end of the period, spreading storm activity beyond typical mountain-focused patterns.
The consistency of afternoon storms this week reflects the combined influence of the ITCZ and passing tropical waves. Expect daily thunderstorm development rather than occasional isolated cells.
Mostly cloudy conditions persist nationwide with moderate rainfall along the Pacific coast and Northern Zone. The Central Valley and Caribbean regions maintain rainfall potential, accompanied by fog bank development in the Greater Metropolitan Area and mountain ranges.
Nighttime fog can be particularly dense this week given elevated humidity levels, creating challenging driving conditions on mountain routes and elevated valley locations. The fog combines with potential rainfall to create low-visibility situations that require extra caution during evening and overnight travel. My advice, stay off the roads at night!
Tuesday Timing: Tropical Wave #39’s arrival shifts rainfall patterns earlier than typical, with overnight Monday into Tuesday morning bringing rain to Caribbean and Northern Zone areas. Plan Tuesday morning activities accordingly.
Mid-to-Late Week Preparation: As TW#40’s potential influence arrives Wednesday onward, rainfall coverage and intensity increase across Pacific regions. Schedule critical outdoor activities for early week if possible.
Saturated Area Caution: Guanacaste, Nicoya Peninsula, Northern Zone, and South Pacific residents should exercise particular vigilance given high soil saturation. Even moderate rainfall can trigger flooding or landslides in vulnerable areas.
Urban Drainage Awareness: City dwellers should be mindful of stormwater drainage capacity during heavy afternoon and evening storms, particularly in areas with known flooding issues.
Given active weather conditions and saturated soils, the National Meteorological Institute advises:
Flood-Prone Areas: Exercise caution where streams or drainage systems may become overwhelmed by water accumulation. Urban areas with limited drainage capacity face particular vulnerability.
Thunderstorm Safety: When thunderstorms approach or strong wind gusts develop near storm clouds, seek shelter in safe locations. Winds can reach up to 80 km/h (50 mph) in isolated cases, potentially causing falling tree branches, downed power lines, or other hazards.
Temperatures remain within typical October ranges, moderated by persistent cloud cover and regular rainfall activity:
| Region | High °C (°F) | Low °C (°F) |
|---|---|---|
| Central Valley | 31° (87.8°) | 14° (57.2°) |
| North Pacific | 35° (95°) | 19° (66.2°) |
| Central Pacific | 32° (89.6°) | 16° (60.8°) |
| South Pacific | 33° (91.4°) | 16° (60.8°) |
| Caribbean | 31° (87.8°) | 18° (64.4°) |
| Northern Zone | 33° (91.4°) | 17° (62.6°) |
This forecast is based on outlooks from Costa Rica’s National Meteorological Institute (IMN) and the US National Hurricane Center.
