Mercer County (Princeton)
September
Weather in Mercer County, New Jersey for September 2026
Your guide to Mercer County weather in September - trends and predictions
Coastal Flood Advisory - See hour by hour.
So far, September 2026 in Mercer County is slightly warmer than the historical average by 1.6 °F.
The forecast for the next days in Mercer County predicts temperatures to be around 21 °F, close to the historical average.
In general, the average temperature in Mercer County at the beginning of September is 26.6 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 21.3 °F by the end of September.
The climate of Mercer County in September is notably wet, with an average of 15 rainy days, and a total of 169.5 mm of precipitation.
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Temperatures
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15
Dry days
15
Rainy days
0
Snow days
23°/15°
Temperatures
15 km/h
Avg max wind
74 %
Avg humidity
Mercer County Weather September
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Temperatures trend during September in Mercer County
See the weather trend as well as the moving average line
September weather in Mercer County day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Light rain shower | 28° /18° | 1.4 mm | 6 | |
| Sept. 2 |  Partly cloudy | 26° /16° | 0.2 mm | 5 | |
| Sept. 3 |  Sunny | 26° /14° | 20.6 mm | 4 | |
| Sept. 4 | Partly cloudy | 28° /16° | 2.4 mm | 6 | |
| Sept. 5 | Sunny | 28° /17° | 11.7 mm | 6 | |
| Sept. 6 | Patchy rain possible | 27° /18° | 13.6 mm | 7 | |
| Sept. 7 | Light rain shower | 23° /13° | 29.3 mm | 6 | |
| Sept. 8 | Sunny | 25° /10° | 0 mm | 6 | |
| Sept. 9 | Sunny | 25° /13° | 0 mm | 5 | |
| Sept. 10 | Sunny | 26° /16° | 0 mm | 5 | |
| Sept. 11 | Partly cloudy | 27° /15° | 0 mm | 6 | |
| Sept. 12 | Sunny | 26° /14° | 0.1 mm | 6 | |
| Sept. 13 | Sunny | 27° /16° | 11.5 mm | 5 | |
| Sept. 14 | Sunny | 27° /16° | 0.1 mm | 7 | |
| Sept. 15 | Sunny | 25° /14° | 0 mm | 6 | |
| Sept. 16 | Partly cloudy | 26° /15° | 0 mm | 6 | |
| Sept. 17 |  Fog | 23° /17° | 2 mm | 5 | |
| Sept. 18 | Fog | 25° /18° | 0 mm | 6 | |
| Sept. 19 |  Overcast | 24° /16° | 4.1 mm | 4 | |
| Sept. 20 |  Moderate or heavy rain shower | 21° /16° | 5.3 mm | 3 | |
| Sept. 21 | Overcast | 22° /15° | 1 mm | 3 | |
| Sept. 22 | Moderate rain at times | 22° /13° | 1.6 mm | 4 | |
| Sept. 23 | Overcast | 22° /15° | 0.6 mm | 4 | |
| Sept. 24 | Overcast | 20° /10° | 0 mm | 5.2 | |
| Sept. 25 | Overcast | 23° /13° | 0 mm | 5.3 | |
| Sept. 26 |  Light rain | 15° /12° | 20.7 mm | 0.7 | |
| Sept. 27 | Light drizzle | 15° /12° | 10.8 mm | 0.8 | |
| Sept. 28 | Overcast | 23° /15° | 0.1 mm | 3.7 | |
| Sept. 29 | Sunny | 25° /14° | 0 mm | 7 | |
| Sept. 30 | Sunny | 28° /15° | 0 mm | 7 | |
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Important Notice
Our weather forecast for Mercer County in September is based on the analysis of historical data rather than real-time forecast models. While this provides a general overview, weather conditions can change. We recommend that you check the Mercer County forecast closer to your planned date for the most up-to-date weather information.
Change Month
Mercer County in September - FAQ
What are the expected maximum and minimum temperatures in Mercer County during September?
During September, expect a variety of temperatures with highs around 23° and lows near 15°, suitable for diverse activities and preferences.
How much rainfall should be expected in Mercer County during September?
Significant rainfall exceeding 169.5 mm is expected in Mercer County during September, occurring over more than 15 days. Preparing for wet conditions is recommended in your planning.
What are the typical wind conditions in Mercer County during September?
The average wind speed in Mercer County during September is 15 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in Mercer County
Explore the daily rainfall trends and prepare for Mercer Countys September weather 💧
Typically, Mercer County has 15 rainy days in September with a total of 169.5 mm of rainfall.
UV exposure in Mercer County during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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Where is Mercer County?Get accurate weather forecasts for Mercer County, located at latitude 40.349 and longitude -74.659. Stay updated with localized weather information tailored for Mercer County.
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