San Mateo Weather in September
In San Mateo, September brings high daytime temperatures around 28°C (82°F), with nights cooling to 21°C (70°F). This month falls within the rainy season, so expect frequent rainfall.
Rainfall in San Mateo in September
San Mateo is in the rainy season in September, with rain on around 23 days and an average of 522 mm (21 in). With high rainfall totals spread across the month, individual showers can be very heavy. Waterproof gear is strongly recommended.
Temperature in San Mateo in September
Daytime highs in San Mateo in September reach 28°C (82°F), with nights around 21°C (70°F). This gives the month a fairly typical daily rhythm, with warmer afternoons and more comfortable nights. Nights remain mild at 21°C (70°F), making evenings a pleasant time to be outdoors.
Sunshine in San Mateo in September
The area enjoys a moderate level of sunlight, with around 159 hours. It's a good balance between sunny and rainy days.If you're looking for dry conditions and comfortable temperatures, September may not be the ideal month to visit San Mateo. Our weather planner can help you explore destinations with more pleasant weather conditions.
Check the conditions for any month of the year.
For a detailed overview over the year and the best time to visit Costa Rica, check out our San Mateo's climate page.
San Mateo Temperature in September
Min Temperature
21°C (70°F)
Max Temperature
28°C (82°F)
Chance of Rain
75%
Precipitation
522 mm (21 in)
Rainy days
23 days
Sunshine
159 hours *
Percentage Sunshine
*
Daily Historical Temperatures
44-year average (1976-2025)
Based on our historical records, temperatures in San Mateo typically stay consistent throughout September, with daily highs averaging around 28°C (82°F). Nights are pleasant, with lows around 19°C (66°F).
Average temperatures in September
Daily Historical Precipitation
44-year average (1976-2025)
Average daily rainfall for each day of the month based on long-term records.
Average precipitation in September
Historical weather for San Mateo in September
Browse day-by-day weather records for San Mateo spanning 51 years. Select any month and year to see actual temperatures, rainfall, and conditions recorded on each day.
San Mateo historical weather extremes in September
Based on weather observations in San Mateo between 1996 and 2025, these are the recorded extremes during September.
- On September 7, 2009, temperatures climbed to 32°C (90°F), marking the warmest September day on record.
- On September 29, 2010, San Mateo saw its coldest September day with temperatures maxing out at 21°C (70°F).
- Nighttime temperatures dropped to 13°C (55°F) on September 29, 2010, marking the coldest September night on record.
- The wettest September day on record brought 167 mm (6.6 in) of precipitation to San Mateo (September 27, 2019).
Best Places in Costa Rica in September
Find out more about the weather in Costa Rica and which places have the best travel conditions in this month. See all of Costa Rica in September →
perfect weather
pleasant
tolerable
unpleasant
poor
What to Wear in San Mateo in September
Warm weather calls for comfortable, breathable clothing in September. Cotton t-shirts, shorts, light dresses, and sandals are perfect. You might still want a light layer for evenings or air-conditioned places (for example buses). Also bring a poncho, it will rain a lot! Waterproof everything you can. Bring sunglasses since you'll have some sunny periods throughout the monthWhat To Do in San Mateo in September
We rated the following activities from 1 (least suitable) to 10 (best) to do.
Check the conditions for any month of the year.
For a detailed overview over the year and the best time to visit Costa Rica, check out our San Mateo's climate page.
See the full San Mateo climate overview or explore weather in Costa Rica.
