Half Moon Bay weather in September: Half Moon Bay, California: normal highs, lows, rain and records for September
Half Moon Bay in September has a normal high of 66°F and a normal low of 51°F, a daily mean of 59°F, holding near 66°F all month. Measurable precipitation falls on 6 days in a normal September, 0.21 inches in all. (NOAA 1991-2020 normals)
In metric: a normal high of 19°C and low of 11°C, 5 mm of precipitation in September.
- NOAA stationHalf Moon Bay
- Station IDUSC00043714
- Location37.47°N 122.44°W
- Elevation27 ft (8 m)
- Population11,324
- Jan 59° 43°
- Feb 60° 43°
- Mar 60° 44°
- Apr 61° 45°
- May 62° 48°
- Jun 64° 50°
- Jul 65° 53°
- Aug 66° 54°
- Sep 66° 51°
- Oct 66° 48°
- Nov 63° 45°
- Dec 59° 43°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
How warm is Half Moon Bay in September?
The normal high is 66°F and the normal low 51°F, for a daily mean of 58.8°F. September is 0.9°F cooler than August and 1.7°F warmer than October. September is the 2nd warmest month of the year in Half Moon Bay and the 11th wettest. Across the month the normal high rises 1°F, from 66°F on September 1 to 67°F on September 30. From one year to the next September's mean temperature typically moves about 1.9°F either way (NOAA's standard deviation), so roughly two Septembers in three average between 57°F and 61°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 23%).
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in |
|---|---|---|---|---|
| September 1 | 66°F | 53°F | 20% | 1% |
| September 8 | 66°F | 52°F | 20% | 1% |
| September 15 | 66°F | 51°F | 21% | 2% |
| September 22 | 67°F | 51°F | 22% | 2% |
| September 30 | 67°F | 50°F | 23% | 3% |
Every day of September: normal high, low and chance of precipitation (warmest afternoon September 30, coldest night September 30)
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in | Daylight |
|---|---|---|---|---|---|
| September 1 | 66°F | 53°F | 20% | 1% | 13 h |
| September 2 | 66°F | 53°F | 20% | 1% | 13 h |
| September 3 | 66°F | 53°F | 20% | 1% | 13 h |
| September 4 | 66°F | 53°F | 20% | 1% | 12 h 50 min |
| September 5 | 66°F | 53°F | 20% | 1% | 12 h 50 min |
| September 6 | 66°F | 52°F | 20% | 1% | 12 h 50 min |
| September 7 | 66°F | 52°F | 20% | 1% | 12 h 50 min |
| September 8 | 66°F | 52°F | 20% | 1% | 12 h 50 min |
| September 9 | 66°F | 52°F | 21% | 1% | 12 h 40 min |
| September 10 | 66°F | 52°F | 21% | 1% | 12 h 40 min |
| September 11 | 66°F | 52°F | 21% | 1% | 12 h 40 min |
| September 12 | 66°F | 52°F | 21% | 1% | 12 h 40 min |
| September 13 | 66°F | 52°F | 21% | 1% | 12 h 30 min |
| September 14 | 66°F | 52°F | 21% | 1% | 12 h 30 min |
| September 15 | 66°F | 51°F | 21% | 2% | 12 h 30 min |
| September 16 | 66°F | 51°F | 21% | 2% | 12 h 30 min |
| September 17 | 66°F | 51°F | 21% | 2% | 12 h 20 min |
| September 18 | 67°F | 51°F | 21% | 2% | 12 h 20 min |
| September 19 | 67°F | 51°F | 22% | 2% | 12 h 20 min |
| September 20 | 67°F | 51°F | 22% | 2% | 12 h 20 min |
| September 21 | 67°F | 51°F | 22% | 2% | 12 h 10 min |
| September 22 | 67°F | 51°F | 22% | 2% | 12 h 10 min |
| September 23 | 67°F | 50°F | 22% | 2% | 12 h 10 min |
| September 24 | 67°F | 50°F | 22% | 2% | 12 h 10 min |
| September 25 | 67°F | 50°F | 22% | 2% | 12 h 10 min |
| September 26 | 67°F | 50°F | 22% | 3% | 12 h |
| September 27 | 67°F | 50°F | 22% | 3% | 12 h |
| September 28 | 67°F | 50°F | 22% | 3% | 12 h |
| September 29 | 67°F | 50°F | 22% | 3% | 12 h |
| September 30 | 67°F | 50°F | 23% | 3% | 11 h 50 min |
- Normal high
- 66°FSeptember average
- Normal low
- 51°FSeptember average
- Precipitation
- 0.21 inmonth total
- Days with precipitation
- 60.01 inch or more
- Daylight
- 13 h to 11 h 50 minSeptember 1 to September 30
- Days at 70°F or more
- 6
- Days at 80°F or more
- 1
- Sunshine
- 82%of clear-sky sunlight (NASA)
Source: NOAA NCEI 1991-2020 daily normals, station USC00043714; monthly normals. Daylight is computed from the place's latitude with NOAA's solar equations.
Does it rain in Half Moon Bay in September?
On a given September day the chance of 0.01 inch or more is 21% on average, highest around September 30 (23%). In all, 0.21 in falls on 6 days of a normal September.
Source: NOAA NCEI 1991-2020 daily and monthly normals, station USC00043714.
What are the records for September in Half Moon Bay?
The warmest September temperature on this station's record (since 1939) is 92°F, on September 30, 2001; the coldest is 35°F, on September 30, 2007. The wettest September brought 3.66 in (1959).
The September mean against the 1991-2020 normal of 58.8°F: 2021 58.4°F (−0.4), 2022 59.9°F (+1.1), 2023 59.9°F (+1.1), 2024 56.5°F (−2.3), 2025 62.9°F (+4.1), 2026 61.0°F (+2.2). 4 of 6 ran warmer than normal.
| September | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 58.4°F | −0.4°F | 0.18 in |
| 2022 | 59.9°F | +1.1°F | 0.45 in |
| 2023 | 59.9°F | +1.1°F | 0.24 in |
| 2024 | 56.5°F | −2.3°F | 0.14 in |
| 2025 | 62.9°F | +4.1°F | 0.49 in |
| 2026 | 61.0°F | +2.2°F | 0.17 in |
Source: records: ACIS, station USC00043714; recent months: ACIS, station USC00043714. Records and recent months use complete months only.
How does September in Half Moon Bay compare across California?
Across the 219 places PlainClimate covers in California, September normal highs run from 64°F in Eureka to 104°F in Brawley; Half Moon Bay's is 66°F.
Source: NOAA NCEI 1991-2020 monthly normals for every station in the state.
Other months and places
- Half Moon Bay in August66°F by day, 54°F at night
- Half Moon Bay in October66°F by day, 48°F at night
- Half Moon Bay through the yearEvery month, frost dates, records and recent years
- California in SeptemberThe statewide normal and the warmest and coolest places
- Brawley: California's warmest Septembernormal high 104°F