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September Weather in Riverhead, United States

Last updated: June 24, 2025

In September, the average temperature in Riverhead, United States hovers around 21°C (70°F), offering a pleasant climate for outdoor activities. You can expect temperatures to range from a cool 11°C (53°F) to a warm 30°C (86°F). With a total precipitation of 89 mm (3.5 in) spread over 9 days, it's wise to keep an umbrella handy. The average humidity of 68% adds a touch of comfort to this lovely month!

September Temperature in Riverhead

In September in Riverhead, the average temperature is 21°C (70°F), with maximums reaching 30°C (86°F) and minimums dropping to as low as 11°C (53°F). It's an ideal time for travelers, offering pleasant weather for outdoor activities and exploration.

September Weather in Riverhead: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Riverhead, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Riverhead, September typically has an average temperature of 21°C (70°F), with highs reaching up to 30°C (86°F) and lows dropping to around 11°C (53°F).
JanFebMarAprMayJunJulAugSepOctNovDec353640485768757569614941
Data source: Temperature data for Riverhead generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Riverhead

In Riverhead in September, the precipitation amount is 89 mm (3.5 in) during a span of 9 days.

September Precipitation Trends in Riverhead

The chart displays monthly precipitation patterns in Riverhead, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Riverhead, September typically receives around 89 mm (3.5 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec79106101126114761179689139100137
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Riverhead

In Riverhead in September humidity is 68%. With an average temperature of 21°C (70°F), this humidity feels like a warm embrace, making the air feel slightly heavy and sticky, which can be quite exhausting for travelers.

September Average Humidity in Riverhead

This chart illustrates the average monthly humidity levels in Riverhead, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Riverhead is approximately 68%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec84%82%81%78%70%69%62%65%68%74%82%80%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Riverhead

In Riverhead in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Riverhead.

Maximum UV Index Levels in Riverhead for September

The chart shows the monthly maximum UV Index (UVI) for Riverhead in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Riverhead typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec3568910998642
Data source: Riverhead September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How September Weather in Riverhead Compares to Other Months

Weather in Riverhead varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Riverhead, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Riverhead, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather2°C (36°F)79 mm (3.1 inches)84%moderate
February Weather2°C (37°F)106 mm (4.2 inches)82%moderate
March Weather4°C (40°F)101 mm (4.0 inches)81%high
April Weather9°C (49°F)126 mm (5.0 inches)78%very high
May Weather14°C (58°F)114 mm (4.5 inches)69%very high
June Weather20°C (68°F)76 mm (3.0 inches)69%very high
July Weather24°C (75°F)117 mm (4.6 inches)62%very high
August Weather24°C (75°F)96 mm (3.8 inches)65%very high
September Weather21°C (70°F)89 mm (3.5 inches)68%very high
October Weather16°C (61°F)139 mm (5.5 inches)74%high
November Weather9°C (49°F)100 mm (3.9 inches)82%moderate
December Weather5°C (41°F)137 mm (5.4 inches)80%low

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