Last updated: February 24, 2025
In September, the weather in Princeton, United States showcases a delightful transition from summer to early autumn. Daily maximum temperatures can soar up to 35°C (95°F), while the average settles at a comfortable 21°C (70°F), providing pleasant daytime conditions. However, nights can cool off significantly, with minimum temperatures dropping to 6°C (43°F). Rainfall is a common occurrence, as 87 mm (3.4 inches) of precipitation typically falls over about 10 days, contributing to the area's lush landscapes. The humidity levels hover around 68%, adding a touch of mugginess to the warm days. Overall, September offers a mix of warmth and refreshing rainfall, perfect for enjoying the changing scenery.
In September, Princeton experiences a noticeable transition towards cooler weather as summer fades. The minimum temperature hovers around 6°C (43°F), providing a refreshing crispness to the air, while the average climbs to a comfortable 21°C (70°F), perfect for outdoor activities. Daytime highs can still reach up to 35°C (95°F), echoing the lingering warmth of summer, making this month a delightful blend of moderate warmth and cool evenings. This shift sets the stage for the upcoming fall, as the temperatures progressively dip into the cooler ranges of October and beyond, inviting an elegant palette of autumn colors to the landscape.
September in Princeton marks a transition into fall, with precipitation totaling 87 mm (3.4 in) over 10 days. This amount is significantly lower than the summer months, reflecting a shift from the peak rainfall seen in July and August, which averaged around 139 mm and 135 mm respectively. As the seasons change, September's precipitation serves as a gentle reminder of the approaching cooler weather. With fewer wet days compared to the preceding months, residents experience a more consistent and mild climate, making it a perfect time to enjoy the beauty of early autumn without the interruptions of heavy rain.
September in Princeton brings a noticeable shift in humidity, with levels sitting at 68%. This slight increase from the drier summer months—where July and August boasted 62% and 65%, respectively—signals a transition into the more humid autumn atmosphere. As the year progresses from the sweltering heights of summer, humidity trends show a gradual ascent, peaking in winter months, notably January and February at 84% and 82%. The refreshing change in September not only hints at cooler temperatures ahead but also prepares the landscape for the vibrant fall colors, creating an ideal backdrop for outdoor activities amidst the comfortable, albeit slightly moist, air.
As summer transitions to autumn in Princeton, the UV Index remains significant, with September recording a UV Index of 8, categorized as very high. This reflects a slight decrease from the summer months, where the index peaked at 10, yet it still warrants caution. With a burn time of just 15 minutes, it's crucial for sun lovers to continue prioritizing skin protection. The trend throughout the year indicates a notable increase in UV exposure from the lower indices found in the winter months, highlighting the importance of awareness as the seasons shift. For more insights on UV exposure in Princeton, you can visit Princeton UV Index.
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As summer gracefully transitions into autumn, September in Princeton bathes in a warm embrace of 272 sunshine hours, a delightful continuation of the vibrant sun-drenched days that July and August offered. Although September sees a decrease from the sizzling peak of July's 349 hours, it still stands out as one of the sunniest months of the year. This pleasant surplus of sunlight offers ample opportunities for outdoor activities and community gatherings, perfect for enjoying the beautiful early fall scenery. Following September, October brings a mild drop to 226 hours, hinting at the approaching chill of winter, yet the lingering warmth of September serves as a lovely reminder of summer's enduring spirit.
In Princeton, September enjoys a noteworthy chance of sunny weather, with approximately 49% of days typically featuring sunshine. This slight uptick in sunny conditions marks a notable increase from the summer months, when the likelihood dips as low as 30% in August. Additionally, comparing September to its early autumn counterparts, it remains more favorable than October's 37%, hinting at a lingering warmth before the chill of fall fully sets in. As the seasons transition, September emerges as a pleasant bridge, often graced by bright days that invite outdoor activities and vibrant fall foliage.
As September arrives in Princeton, the summer's long, sun-filled days begin to wane, offering about 12 hours of daylight. This month marks a gentle transition from the vibrant, extended daylight of summer—peaking at 14 hours in June and July—toward the shorter days of fall. As the leaves start to turn and temperatures cool, the gradual reduction in sunlight reflects nature's rhythm, with each month revealing a carefully balanced dance between light and darkness. Following September, daylight slips further as October brings 11 hours and November sees a return to the shorter days of winter, each shift reminding us of the cyclical beauty of the seasons.
As summer gently transitions to fall in Princeton, September presents a subtle increase in wind speed, averaging 2.9 m/s (7 mph). This marks a shift from the calmer breezes of July and August, which hovered around 2.3 m/s (5 mph), indicating that the whisper of autumn is beginning to stir the air. With the sun's warmth still lingering, the mild winds blend seamlessly with the freshening atmosphere, creating a pleasant backdrop for outdoor activities. As the months progress, average wind speeds usually see a slight uptick; for instance, October and November both return to around 3.0 m/s (7 mph) and 3.1 m/s (7 mph), respectively. This trend reflects the gradual intensification of the winds, echoing the seasonal changes as Princeton prepares for the crisp days ahead.
The weather in Princeton changes throughout the year, offering a unique experience in each season. Below is a month-by-month comparison of September's weather with other months, highlighting differences in temperature, precipitation, and other key factors. Click on each section to discover seasonal trends in Princeton and find detailed weather information for every month.
September and January present markedly contrasting weather patterns. In September, temperatures range from a mild 6°C (43°F) to a scorching 35°C (95°F), with an average of 21°C (70°F), making it a vibrant and warm month. The humidity sits at 68%, and the month experiences about 87 mm (3.4 in) of precipitation over roughly 10 days. Conversely, January is defined by an average temperature of just 2°C (35°F), with nighttime lows plummeting to -17°C (2°F) and daytime highs peaking at 20°C (68°F). Although precipitation during January is slightly lower at 64 mm (2.5 in) over 8 days, the humidity is higher at 84%, giving the month a distinctly colder and more damp feel. For more detailed insights about the winter climate, you can visit Princeton weather in January.
September and February present stark contrasts in weather conditions. In September, the climate is generally warm, with average temperatures around 21°C (70°F) and maximums reaching up to 35°C (95°F). The month experiences occasional rain, totaling about 87 mm (3.4 inches) over approximately 10 days, and the humidity sits at a moderate 68%. In contrast, February is characterized by much colder temperatures, with averages dipping to just 3°C (38°F) and minimums plummeting to -16°C (4°F). The precipitation increases slightly to 109 mm (4.3 inches) across 11 days, and the humidity rises to 82%, creating a much chillier atmosphere. For more detailed insights, you can refer to Princeton weather in February.
September and March present contrasting weather profiles. In September, temperatures range from a mild 6°C (43°F) at night to a warm 35°C (95°F) during the day, offering an average of 21°C (70°F). The month sees about 87 mm (3.4 in) of precipitation over 10 days, with a relative humidity of 68%. In contrast, March experiences much cooler temperatures, with a minimum of -12°C (10°F) and a maximum of 28°C (83°F), averaging only 6°C (43°F). Despite March being wetter, with 109 mm (4.3 in) of precipitation over the same number of days, humidity levels rise slightly to 81%. For a detailed look at March weather, you can check Princeton weather in March.
When comparing the weather in September and April, notable differences emerge in temperature and precipitation. September typically sees milder conditions with an average temperature of 21°C (70°F) and a maximum of 35°C (95°F), while April has cooler temperatures, averaging 12°C (54°F) with a high of 31°C (88°F). Precipitation is slightly higher in April, with 106 mm (4.2 in) over 12 days compared to September’s 87 mm (3.4 in) over 10 days, and April also experiences a higher humidity level of 78% compared to September's 68%. For a detailed overview of April weather, you can visit Princeton weather in April.
September and May present quite different weather profiles. In September, temperatures range from a minimum of 6°C (43°F) to a maximum of 35°C (95°F), with an average temperature of 21°C (70°F). The month sees about 87 mm (3.4 in) of precipitation over roughly 10 days, accompanied by humidity levels around 68%. In contrast, May experiences cooler minimum temperatures as low as 1°C (35°F) and an average of 17°C (63°F), while also peaking at 35°C (94°F). Precipitation is higher at 131 mm (5.1 in) spread over 13 days, with similar humidity levels of 69%. For more detailed insights into the weather patterns, you can visit Princeton weather in May.
When comparing the weather in September and June, both months exhibit somewhat similar temperature ranges, with June slightly warmer overall. In June, temperatures range from a minimum of 9°C (48°F) to a maximum of 36°C (97°F), with an average of 22°C (73°F), whereas September has a minimum of 6°C (43°F) and a maximum of 35°C (95°F), averaging around 21°C (70°F). Precipitation is a bit higher in June, totaling 100 mm (3.9 in) over 12 days, compared to September's 87 mm (3.4 in) over 10 days. Both months share comparable humidity levels, with September at 68% and June at 69%. For a more detailed overview of June weather, you can check Princeton weather in June.
In comparing the weather between September and July, September tends to be slightly cooler, with average temperatures ranging from a minimum of 6°C (43°F) to a maximum of 35°C (95°F), while July experiences milder nights and hotter days, with temperatures ranging from 13°C (56°F) to 37°C (98°F). July also sees higher average temperatures, peaking at around 26°C (78°F), compared to September's average of 21°C (70°F). In terms of precipitation, July is wetter, receiving 139 mm (5.5 in) over 14 days, in contrast to September's 87 mm (3.4 in) spread over 10 days. Humidity levels are slightly higher in September at 68%, compared to July's 62%. For more details on July weather, you can visit Princeton weather in July.
September weather in Princeton shows a notable shift compared to August. While both months experience similar maximum temperatures, with September peaking at 35°C (95°F) and August at 35°C (96°F), September boasts a lower average temperature of 21°C (70°F) compared to August's warmer 24°C (76°F). Precipitation in September is reduced to 87 mm (3.4 in) over 10 days, down from August’s higher 135 mm (5.3 in) over 14 days, indicating drier conditions as summer transitions to fall. Additionally, September’s humidity is slightly higher at 68%, compared to 65% in August. For more detailed insights on August weather, check out Princeton weather in August.
September and October present a notable shift in weather patterns. In September, temperatures range from a minimum of 6°C (43°F) to an average of 21°C (70°F), peaking at 35°C (95°F), alongside a relatively comfortable humidity level of 68% and precipitation totaling 87 mm (3.4 in) over about 10 days. By contrast, October experiences cooler temperatures, with a minimum of 1°C (34°F) and an average of 16°C (61°F), while still reaching similar highs of 35°C (96°F). However, October is characterized by increased precipitation, climbing to 121 mm (4.8 in) over the same number of days, alongside a slightly higher humidity of 74%. For more detailed insights into October's weather, visit Princeton weather in October.
September and November display striking contrasts in weather conditions. September typically enjoys mild to warm temperatures, ranging from a minimum of 6°C (43°F) to a maximum of 35°C (95°F), with an average of 21°C (70°F). The month experiences about 87 mm (3.4 in) of precipitation over approximately 10 days, alongside a relative humidity of 68%. In contrast, November brings cooler weather, with temperatures dropping significantly, from a minimum of -9°C (15°F) to a maximum of 25°C (77°F) and an average of just 8°C (46°F). While precipitation levels are slightly lower at 83 mm (3.3 in) over 9 days, the humidity rises to 82%, creating a notably different atmosphere. For more details, check Princeton weather in November.
September and December present markedly different weather patterns. In September, temperatures range from a mild 21°C (70°F) on average, reaching highs of 35°C (95°F), while the minimum temperature remains relatively warm at 6°C (43°F). The humidity is moderate at 68%, and precipitation occurs over 10 days, totaling 87 mm (3.4 in). In contrast, December brings a significant drop in temperatures, with an average of just 4°C (39°F), and lows plummeting to -12°C (11°F). The maximum temperature reaches a comfortable 19°C (67°F), but the humidity increases to 80%. Precipitation is slightly higher in December, accumulating 104 mm (4.1 in) over the same number of days. For more detailed insights into December's weather, you can visit Princeton weather in December.
September in Princeton brings a delightful transition from the heat of summer, with average temperatures settling around a comfortable 21°C (70°F). Unlike the warmer months that boast relentless heat, September’s highs can still reach 35°C (95°F), but cool nights can drop as low as 6°C (43°F), offering refreshing relief and a hint of autumn’s approach. While rain visits the area approximately 10 days during the month, totaling about 87 mm (3.4 in), the humidity remains at a moderate 68%, lending the air a pleasant crispness that contrasts sharply with the muggy conditions often seen in summer. This unique period of fluctuating temperatures and a refreshing atmosphere marks September as a time of transformation in Princeton. For more insights into the area's distinct weather patterns, check out Princeton Climate.