Allentown weather in September: Allentown, Pennsylvania: normal highs, lows, rain and records for September
Allentown in September has a normal high of 77°F and a normal low of 55°F, a daily mean of 66°F, falling from 82°F on the 1st to 72°F by the 30th. Measurable precipitation falls on 10 days in a normal September, 4.84 inches in all. (NOAA 1991-2020 normals)
In metric: a normal high of 25°C and low of 13°C, 123 mm of precipitation in September.
- NOAA stationAllentown Lehigh Valley International Airport
- Station IDUSW00014737
- Location40.65°N 75.45°W
- Elevation390 ft (119 m)
- From the center4 miles
- Population127,138
- Jan 38° 22°
- Feb 42° 23°
- Mar 51° 31°
- Apr 63° 40°
- May 74° 51°
- Jun 82° 60°
- Jul 86° 65°
- Aug 84° 63°
- Sep 77° 55°
- Oct 66° 44°
- Nov 54° 34°
- Dec 43° 27°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
How warm is Allentown in September?
The normal high is 77°F and the normal low 55°F, for a daily mean of 66.3°F. September is 7.3°F cooler than August and 11.7°F warmer than October. September is the 4th warmest month of the year in Allentown and the 2nd wettest. Across the month the normal high falls 10°F, from 82°F on September 1 to 72°F on September 30. From one year to the next September's mean temperature typically moves about 2.3°F either way (NOAA's standard deviation), so roughly two Septembers in three average between 64°F and 69°F.
Bars above: each day's normal high to low. Columns below: the chance of 0.01 inch or more of precipitation that day, on a scale of 0 to 100% (highest 33%).
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in |
|---|---|---|---|---|
| September 1 | 82°F | 60°F | 31% | 21% |
| September 8 | 80°F | 58°F | 31% | 20% |
| September 15 | 78°F | 56°F | 31% | 21% |
| September 22 | 75°F | 53°F | 32% | 21% |
| September 30 | 72°F | 50°F | 33% | 21% |
Every day of September: normal high, low and chance of precipitation (warmest afternoon September 1, coldest night September 30)
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in | Daylight |
|---|---|---|---|---|---|
| September 1 | 82°F | 60°F | 31% | 21% | 13 h 10 min |
| September 2 | 82°F | 60°F | 31% | 21% | 13 h 10 min |
| September 3 | 82°F | 59°F | 31% | 21% | 13 h |
| September 4 | 81°F | 59°F | 31% | 21% | 13 h |
| September 5 | 81°F | 59°F | 31% | 21% | 13 h |
| September 6 | 81°F | 59°F | 31% | 21% | 13 h |
| September 7 | 81°F | 58°F | 31% | 20% | 12 h 50 min |
| September 8 | 80°F | 58°F | 31% | 20% | 12 h 50 min |
| September 9 | 80°F | 58°F | 31% | 20% | 12 h 50 min |
| September 10 | 80°F | 57°F | 31% | 20% | 12 h 50 min |
| September 11 | 79°F | 57°F | 31% | 20% | 12 h 40 min |
| September 12 | 79°F | 57°F | 31% | 20% | 12 h 40 min |
| September 13 | 79°F | 56°F | 31% | 21% | 12 h 40 min |
| September 14 | 78°F | 56°F | 31% | 21% | 12 h 30 min |
| September 15 | 78°F | 56°F | 31% | 21% | 12 h 30 min |
| September 16 | 78°F | 55°F | 31% | 21% | 12 h 30 min |
| September 17 | 77°F | 55°F | 31% | 21% | 12 h 30 min |
| September 18 | 77°F | 55°F | 32% | 21% | 12 h 20 min |
| September 19 | 76°F | 54°F | 32% | 21% | 12 h 20 min |
| September 20 | 76°F | 54°F | 32% | 21% | 12 h 20 min |
| September 21 | 76°F | 53°F | 32% | 21% | 12 h 20 min |
| September 22 | 75°F | 53°F | 32% | 21% | 12 h 10 min |
| September 23 | 75°F | 53°F | 33% | 21% | 12 h 10 min |
| September 24 | 74°F | 52°F | 33% | 21% | 12 h 10 min |
| September 25 | 74°F | 52°F | 33% | 21% | 12 h 10 min |
| September 26 | 74°F | 51°F | 33% | 21% | 12 h |
| September 27 | 73°F | 51°F | 33% | 21% | 12 h |
| September 28 | 73°F | 51°F | 33% | 21% | 12 h |
| September 29 | 72°F | 50°F | 33% | 21% | 11 h 50 min |
| September 30 | 72°F | 50°F | 33% | 21% | 11 h 50 min |
- Normal high
- 77°FSeptember average
- Normal low
- 55°FSeptember average
- Precipitation
- 4.84 inmonth total
- Days with precipitation
- 100.01 inch or more
- Days at 90°F or more
- 2
- Daylight
- 13 h 10 min to 11 h 50 minSeptember 1 to September 30
- Days at 70°F or more
- 25
- Days at 80°F or more
- 11
- Sunshine
- 75%of clear-sky sunlight (NASA)
Source: NOAA NCEI 1991-2020 daily normals, station USW00014737; monthly normals. Daylight is computed from the place's latitude with NOAA's solar equations.
Does it rain in Allentown in September?
On a given September day the chance of 0.01 inch or more is 32% on average, highest around September 29 (33%). In all, 4.84 in falls on 10 days of a normal September, 2 of them with an inch or more.
In a normal September in Allentown, 2 days reach 90°F.
Source: NOAA NCEI 1991-2020 daily and monthly normals, station USW00014737.
How humid and windy is Allentown in September?
At 3 p.m. the normal temperature is 69°F with 53% relative humidity and a dew point of 51°F; at 6 a.m. it is 53°F with 88% humidity. The wind averages 6.1 mph, most often from the west in the afternoon.
| Time | Temperature | Dew point | Humidity | Wind | Clear or few clouds |
|---|---|---|---|---|---|
| 6 a.m. | 53°F | 49°F | 88% | 4.5 mph | 54% |
| 9 a.m. | 60°F | 52°F | 74% | 6.7 mph | 55% |
| noon | 67°F | 52°F | 58% | 8.5 mph | 51% |
| 3 p.m. | 69°F | 51°F | 53% | 8.9 mph | 53% |
| 6 p.m. | 64°F | 51°F | 62% | 6.2 mph | 64% |
| 9 p.m. | 59°F | 52°F | 77% | 4.9 mph | 67% |
Source: NOAA NCEI 1991-2020 hourly normals, station USW00014737. Hourly normals exist only for NOAA's first-order stations; a dash where NOAA publishes no value for that hour (the sky at some hours).
What are the records for September in Allentown?
The warmest September temperature on Allentown's official record (since 1922) is 99°F, on September 3, 1953; the coldest is 30°F, on September 28, 1947. The wettest September brought 12.99 in (2011).
The September mean against the 1991-2020 normal of 66.3°F: 2021 66.4°F (+0.1), 2022 64.9°F (−1.4), 2023 65.8°F (−0.5), 2024 65.2°F (−1.1), 2025 67.6°F (+1.3), 2026 67.2°F (+0.9). 3 of 6 ran warmer than normal.
| September | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 66.4°F | +0.1°F | 8.12 in |
| 2022 | 64.9°F | −1.4°F | 3.47 in |
| 2023 | 65.8°F | −0.5°F | 4.03 in |
| 2024 | 65.2°F | −1.1°F | 1.30 in |
| 2025 | 67.6°F | +1.3°F | 2.66 in |
| 2026 | 67.2°F | +0.9°F | 4.44 in |
Source: records: ACIS, NWS threaded record ABEthr; recent months: ACIS, station USW00014737. Records and recent months use complete months only.
How does September in Allentown compare across Pennsylvania?
Across the 108 places PlainClimate covers in Pennsylvania, September normal highs run from 68°F in Laporte to 80°F in Marcus Hook; Allentown's is 77°F.
Source: NOAA NCEI 1991-2020 monthly normals for every station in the state.
Other months and places
- Allentown in August84°F by day, 63°F at night
- Allentown in October66°F by day, 44°F at night
- Allentown through the yearEvery month, frost dates, records and recent years
- Pennsylvania in SeptemberThe statewide normal and the warmest and coolest places
- Marcus Hook: Pennsylvania's warmest Septembernormal high 80°F