September is one of the warmer months of the year in Harlingen, with average highs near 32.6°C and lows around 24.9°C (mean 28.8°C). It is a relatively wet time of year, averaging 125 mm of rainfall and 73% relative humidity across the period.
September is one of the warmer months of the year in Harlingen. Across 45 years of records, the warmest September in Harlingen was 2023 — when the month averaged 32.2°C — while the coldest was 1984 at 26.4°C. Typical September days reach 32.6°C with nights near 24.9°C. The long-term trend is warming, about 0.4°C per decade.
September is a relatively wet time of year in Harlingen, averaging 125 mm of rainfall. The wettest September on record was 1984 with 314 mm, while the driest was 2011 at 14 mm.
Relative humidity in Harlingen during September averages 73%. The most humid September was 2014 at 81%, and the least humid was 2011 at 62%.
September receives about 5.2 kWh/m²/day of solar energy in Harlingen. The sunniest September was 2023 at 6.1 kWh/m²/day, and the cloudiest was 1984 at 4.1.
Average wind speed in Harlingen during September is 2.9 m/s. The windiest September was 1986 at 3.7 m/s, while the calmest was 2007 at 2.1 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 28.4°C | 28.3°C | 28.4°C | 29.2°C | 29.8°C | +1.4°C |
| Avg High | 32.3°C | 32.0°C | 32.2°C | 33.0°C | 34.0°C | +1.7°C |
| Avg Low | 24.5°C | 24.5°C | 24.6°C | 25.4°C | 25.5°C | +1°C |
| Avg Rain | 120 mm | 121 mm | 154 mm | 126 mm | 91 mm | -29 mm |
September temperatures in Harlingen have risen by about 2°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 15.4°C (2020) to a record high of 40.3°C (2005).
Rainfall in September is a relatively wet time of year, averaging 125 mm, with a wettest year of 314 mm.
A quieter season to visit Harlingen
If your dates are flexible, the more temperate months of March and November tend to be the most comfortable for visiting Harlingen. That said, September — with days averaging 32.6°C and nights around 24.9°C (mean 28.8°C) and higher rainfall (125 mm) — can still be rewarding for travellers who don't mind the warmth, and often means fewer crowds.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 34.4°C | 30.3°C | 26.1°C | 38.3°C | 22.9°C | 71 mm | 69% | 2.6 m/s | 5.5 |
| 2024 | 33.1°C | 29.2°C | 25.4°C | 35.6°C | 21.6°C | 201 mm | 78% | 2.7 m/s | 4.9 |
| 2023 🔥 | 37.3°C | 32.2°C | 27.1°C | 39.6°C | 24.6°C | 14 mm | 64% | 2.9 m/s | 6.1 |
| 2022 | 33.3°C | 29.2°C | 25.1°C | 35.6°C | 20.9°C | 90 mm | 70% | 2.3 m/s | 5.3 |
| 2021 | 33.5°C | 29.4°C | 25.3°C | 36.2°C | 20.2°C | 61 mm | 71% | 2.8 m/s | 5.6 |
| 2020 | 32.2°C | 28.2°C | 24.2°C | 35.2°C | 15.4°C | 108 mm | 75% | 3.3 m/s | 4.8 |
| 2019 | 33.3°C | 29.9°C | 26.4°C | 36.5°C | 24.8°C | 91 mm | 74% | 3.3 m/s | 5.2 |
| 2018 | 32.1°C | 28.9°C | 25.7°C | 36.0°C | 22.9°C | 153 mm | 78% | 2.6 m/s | 4.7 |
| 2017 | 34.0°C | 29.8°C | 25.5°C | 36.7°C | 20.4°C | 63 mm | 67% | 3.4 m/s | 5.3 |
| 2016 | 34.3°C | 30.3°C | 26.3°C | 36.9°C | 23.1°C | 55 mm | 69% | 2.9 m/s | 5.6 |
| 2015 | 32.9°C | 29.0°C | 25.0°C | 36.0°C | 20.5°C | 120 mm | 74% | 2.8 m/s | 5.5 |
| 2014 | 31.2°C | 28.3°C | 25.3°C | 35.2°C | 22.7°C | 257 mm | 81% | 2.9 m/s | 4.8 |
| 2013 | 31.4°C | 28.2°C | 24.9°C | 36.0°C | 19.5°C | 227 mm | 79% | 3 m/s | 4.8 |
| 2012 | 34.0°C | 29.6°C | 25.2°C | 37.4°C | 22.2°C | 52 mm | 67% | 3.3 m/s | 5.6 |
| 2011 | 35.4°C | 30.2°C | 25.0°C | 38.5°C | 21.0°C | 14 mm | 62% | 3 m/s | 5.9 |
| 2010 | 31.5°C | 28.2°C | 24.9°C | 34.6°C | 16.9°C | 227 mm | 78% | 2.8 m/s | 5 |
| 2009 | 32.5°C | 28.6°C | 24.7°C | 37.2°C | 19.1°C | 183 mm | 75% | 2.5 m/s | 4.8 |
| 2008 | 30.8°C | 26.9°C | 23.1°C | 36.3°C | 17.5°C | 181 mm | 78% | 2.7 m/s | 5 |
| 2007 | 31.4°C | 28.2°C | 24.9°C | 34.1°C | 22.2°C | 125 mm | 80% | 2.1 m/s | 5.3 |
| 2006 | 32.0°C | 28.4°C | 24.8°C | 36.3°C | 20.4°C | 203 mm | 75% | 3 m/s | 5.1 |
| 2005 | 34.4°C | 30.2°C | 26.0°C | 40.3°C | 24.5°C | 65 mm | 70% | 2.8 m/s | 5.4 |
| 2004 | 32.5°C | 28.7°C | 24.9°C | 35.8°C | 22.3°C | 140 mm | 74% | 2.5 m/s | 5.3 |
| 2003 | 30.7°C | 27.7°C | 24.8°C | 34.0°C | 21.4°C | 292 mm | 80% | 2.6 m/s | 4.7 |
| 2002 | 32.5°C | 28.3°C | 24.2°C | 37.6°C | 19.6°C | 194 mm | 74% | 3 m/s | 5.3 |
| 2001 | 31.8°C | 28.0°C | 24.2°C | 35.4°C | 19.2°C | 128 mm | 75% | 3.2 m/s | 5.5 |
| 2000 | 33.8°C | 29.0°C | 24.3°C | 39.7°C | 18.0°C | 32 mm | 66% | 3.2 m/s | 5.7 |
| 1999 | 32.2°C | 28.0°C | 23.8°C | 36.1°C | 19.8°C | 109 mm | 72% | 2.9 m/s | 5.5 |
| 1998 | 32.0°C | 28.6°C | 25.1°C | 36.1°C | 22.4°C | 235 mm | 80% | 2.8 m/s | 4.6 |
| 1997 | 32.8°C | 28.8°C | 24.7°C | 36.0°C | 20.6°C | 107 mm | 72% | 2.6 m/s | 5.5 |
| 1996 | 31.5°C | 28.1°C | 24.6°C | 34.2°C | 18.5°C | 114 mm | 79% | 3 m/s | 5.4 |
| 1995 | 33.0°C | 28.9°C | 24.8°C | 35.5°C | 16.1°C | 76 mm | 72% | 2.6 m/s | 5.4 |
| 1994 | 32.5°C | 28.0°C | 23.6°C | 35.8°C | 18.6°C | 89 mm | 69% | 2.5 m/s | 5.3 |
| 1993 | 31.5°C | 28.0°C | 24.5°C | 35.7°C | 19.1°C | 150 mm | 76% | 2.9 m/s | 5.3 |
| 1992 | 32.3°C | 28.6°C | 24.9°C | 36.2°C | 19.9°C | 93 mm | 71% | 3.4 m/s | 5.1 |
| 1991 | 30.4°C | 27.2°C | 24.0°C | 34.1°C | 16.3°C | 146 mm | 78% | 2.7 m/s | 4.8 |
| 1990 | 31.9°C | 28.3°C | 24.7°C | 34.2°C | 22.2°C | 92 mm | 73% | 2.5 m/s | 5 |
| 1989 | 32.7°C | 28.2°C | 23.8°C | 35.7°C | 16.1°C | 45 mm | 65% | 3.1 m/s | 5.7 |
| 1988 | 32.0°C | 28.1°C | 24.1°C | 34.7°C | 20.6°C | 162 mm | 74% | 3.6 m/s | 5.2 |
| 1987 | 33.4°C | 29.1°C | 24.8°C | 37.5°C | 19.3°C | 126 mm | 69% | 3.2 m/s | 5.4 |
| 1986 | 33.1°C | 29.5°C | 25.8°C | 35.0°C | 24.5°C | 63 mm | 72% | 3.7 m/s | 5.1 |
| 1985 | 32.6°C | 28.8°C | 25.0°C | 36.5°C | 16.6°C | 125 mm | 72% | 3.4 m/s | 5.3 |
| 1984 ❄️ 🌧️ | 29.5°C | 26.4°C | 23.3°C | 34.2°C | 15.7°C | 314 mm | 80% | 3.5 m/s | 4.1 |
| 1983 | 31.3°C | 27.8°C | 24.4°C | 36.5°C | 17.4°C | 143 mm | 76% | 3.2 m/s | — |
| 1982 | 33.5°C | 29.1°C | 24.8°C | 36.7°C | 20.8°C | 37 mm | 67% | 3 m/s | — |
| 1981 | 32.5°C | 28.5°C | 24.5°C | 35.2°C | 18.0°C | 65 mm | 71% | 2.9 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 32.6°C with lows near 24.9°C (mean 28.8°C), based on 45 years of NASA POWER data.
September averages 125 mm of rainfall in Harlingen, a relatively wet time of year. The wettest on record was 314 mm in 1984.
The hottest September reached 40.3°C in 2005. The coldest dipped to 15.4°C in 2020.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2°C. Daytime highs moved from 31.9°C to 34.3°C and overnight lows from 24.4°C to 25.8°C over the same span.
September is one of the warmer months of the year in Harlingen and a relatively wet time of year, so plan for around 32.6°C daytime highs and 24.9°C at night.
Not quite — September is the 9th coolest month in Harlingen, averaging 28.8°C.
For September in Harlingen, pack light, breathable clothing and sun protection, with typical highs of 32.6°C and lows of 24.9°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 73% — moderately humid.
Average wind speed in September is 2.9 m/s. The windiest September on record averaged 3.7 m/s (1986).
The wettest September on record was 1984 with 314 mm. On average, September sees 125 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Harlingen behaves each September, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for September specifically, along with year-by-year records and how the month has changed over the decades.
