December is one of the warmer months of the year in Halfmoon Bay, with average highs near 13.9°C and lows around 10.2°C (mean 12.1°C). It is about average for rainfall, averaging 110 mm of rainfall and 81% relative humidity across the period.
December is one of the warmer months of the year in Halfmoon Bay. Across 45 years of records, the warmest Decembers in Halfmoon Bay were 2005 and 2017 — when the month averaged 14.2°C — while the coldest was 2004 at 9.5°C. Typical December days reach 13.9°C with nights near 10.2°C. The long-term trend is warming, about 0.2°C per decade.
December is about average for rainfall in Halfmoon Bay, averaging 110 mm of rainfall. The wettest December on record was 2004 with 189 mm, while the driest was 2018 at 48 mm.
Relative humidity in Halfmoon Bay during December averages 81%. The most humid December was 2005 at 85%, and the least humid was 1989 at 77%.
December receives about 6.1 kWh/m²/day of solar energy in Halfmoon Bay. The sunniest December was 2011 at 6.8 kWh/m²/day, and the cloudiest was 1984 at 5.3.
Average wind speed in Halfmoon Bay during December is 3.9 m/s. The windiest December was 1990 at 5.1 m/s, while the calmest was 2011 at 2.7 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 12.1°C | 11.6°C | 11.8°C | 12.5°C | 12.4°C | +0.3°C |
| Avg High | 13.9°C | 13.4°C | 13.6°C | 14.4°C | 14.2°C | +0.3°C |
| Avg Low | 10.3°C | 9.6°C | 10.0°C | 10.6°C | 10.6°C | +0.3°C |
| Avg Rain | 127 mm | 113 mm | 114 mm | 95 mm | 95 mm | -32 mm |
December temperatures in Halfmoon Bay have risen by about 0.5°C between 1981–1985 and 2021–2025.
December has ranged from a record low of 6°C (1997) to a record high of 20.6°C (2014).
Rainfall in December is about average for rainfall, averaging 110 mm, with a wettest year of 189 mm.
One of the best times to visit Halfmoon Bay
December is one of the best times to visit Halfmoon Bay. Expect days averaging 13.9°C and nights around 10.2°C (mean 12.1°C) — warmer than Halfmoon Bay's yearly average — with higher rainfall (110 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 13.6°C | 12.0°C | 10.3°C | 17.9°C | 7.3°C | 109 mm | 79% | 3.9 m/s | — |
| 2024 | 14.5°C | 12.9°C | 11.3°C | 18.7°C | 8.2°C | 135 mm | 85% | 3.9 m/s | 5.7 |
| 2023 | 14.2°C | 12.2°C | 10.2°C | 20.4°C | 8.0°C | 90 mm | 80% | 4 m/s | 6 |
| 2022 | 14.8°C | 12.9°C | 11.0°C | 19.7°C | 7.8°C | 63 mm | 82% | 3.3 m/s | 6 |
| 2021 | 14.4°C | 12.6°C | 10.8°C | 18.5°C | 8.6°C | 71 mm | 80% | 4.3 m/s | 6.4 |
| 2020 | 13.8°C | 11.9°C | 10.0°C | 16.4°C | 6.0°C | 103 mm | 80% | 4.2 m/s | 6.1 |
| 2019 | 13.4°C | 11.8°C | 10.2°C | 18.8°C | 8.7°C | 149 mm | 80% | 4.2 m/s | 5.4 |
| 2018 | 15.1°C | 13.2°C | 11.3°C | 19.6°C | 8.9°C | 48 mm | 80% | 3.5 m/s | 6.6 |
| 2017 | 16.1°C | 14.2°C | 12.4°C | 19.2°C | 9.4°C | 84 mm | 78% | 3.3 m/s | 6.3 |
| 2016 | 13.9°C | 11.9°C | 10.0°C | 19.8°C | 7.7°C | 75 mm | 78% | 4.4 m/s | 6.2 |
| 2015 | 13.8°C | 11.8°C | 9.7°C | 20.4°C | 7.8°C | 79 mm | 80% | 4.3 m/s | 6.4 |
| 2014 | 14.4°C | 12.2°C | 10.0°C | 20.6°C | 6.5°C | 92 mm | 82% | 3 m/s | 6.3 |
| 2013 | 13.9°C | 12.2°C | 10.5°C | 17.7°C | 7.6°C | 117 mm | 84% | 3.9 m/s | 5.8 |
| 2012 | 14.3°C | 12.5°C | 10.7°C | 18.2°C | 9.2°C | 139 mm | 81% | 3.8 m/s | 6.3 |
| 2011 | 15.0°C | 13.0°C | 11.0°C | 18.6°C | 8.4°C | 52 mm | 81% | 2.7 m/s | 6.8 |
| 2010 | 14.4°C | 12.5°C | 10.6°C | 19.9°C | 7.1°C | 118 mm | 81% | 4.3 m/s | 5.7 |
| 2009 | 13.1°C | 11.3°C | 9.4°C | 16.7°C | 6.8°C | 123 mm | 80% | 4.1 m/s | 5.8 |
| 2008 | 13.5°C | 11.7°C | 10.0°C | 18.4°C | 6.9°C | 95 mm | 81% | 3.6 m/s | 5.8 |
| 2007 | 14.1°C | 12.2°C | 10.2°C | 19.1°C | 8.2°C | 108 mm | 81% | 3.4 m/s | 6.2 |
| 2006 | 12.2°C | 10.5°C | 8.9°C | 15.5°C | 6.9°C | 91 mm | 81% | 3.9 m/s | 5.6 |
| 2005 🔥 | 16.0°C | 14.2°C | 12.3°C | 18.9°C | 9.0°C | 125 mm | 85% | 3.4 m/s | 5.9 |
| 2004 ❄️ 🌧️ | 11.0°C | 9.5°C | 8.1°C | 16.3°C | 6.9°C | 189 mm | 82% | 4.7 m/s | 5.4 |
| 2003 | 13.5°C | 11.5°C | 9.5°C | 19.1°C | 6.9°C | 99 mm | 79% | 4.3 m/s | 6.5 |
| 2002 | 13.4°C | 11.6°C | 9.8°C | 16.7°C | 7.8°C | 123 mm | 82% | 4.2 m/s | 6.1 |
| 2001 | 14.4°C | 12.9°C | 11.3°C | 20.4°C | 8.6°C | 80 mm | 82% | 3.6 m/s | 5.7 |
| 2000 | 14.5°C | 12.5°C | 10.5°C | 18.2°C | 7.6°C | 109 mm | 80% | 4.1 m/s | 6.1 |
| 1999 | 13.7°C | 11.8°C | 9.9°C | 17.7°C | 7.7°C | 67 mm | 78% | 3.9 m/s | 6.1 |
| 1998 | 13.8°C | 12.0°C | 10.1°C | 19.4°C | 7.6°C | 92 mm | 82% | 3.9 m/s | 5.8 |
| 1997 | 12.5°C | 10.5°C | 8.5°C | 18.4°C | 6.0°C | 145 mm | 80% | 4.4 m/s | 6 |
| 1996 | 13.5°C | 11.7°C | 9.9°C | 17.6°C | 7.6°C | 82 mm | 79% | 4 m/s | 6.1 |
| 1995 | 13.6°C | 11.8°C | 9.9°C | 18.0°C | 7.0°C | 185 mm | 82% | 3.6 m/s | 5.6 |
| 1994 | 13.3°C | 11.4°C | 9.5°C | 18.1°C | 6.7°C | 106 mm | 79% | 4.7 m/s | 6.7 |
| 1993 | 13.2°C | 11.5°C | 9.7°C | 17.5°C | 7.2°C | 128 mm | 83% | 3.6 m/s | 5.8 |
| 1992 | 13.3°C | 11.2°C | 9.1°C | 18.3°C | 6.2°C | 101 mm | 78% | 3.7 m/s | 5.9 |
| 1991 | 13.5°C | 11.6°C | 9.7°C | 17.6°C | 6.1°C | 49 mm | 81% | 3.6 m/s | 6.6 |
| 1990 | 13.8°C | 12.0°C | 10.1°C | 19.0°C | 7.9°C | 174 mm | 78% | 5.1 m/s | 6.4 |
| 1989 | 14.2°C | 12.2°C | 10.3°C | 17.8°C | 7.6°C | 150 mm | 77% | 4.3 m/s | 6.4 |
| 1988 | 15.3°C | 13.2°C | 11.1°C | 19.8°C | 7.1°C | 121 mm | 80% | 3.7 m/s | 6.5 |
| 1987 | 13.0°C | 11.3°C | 9.7°C | 17.4°C | 7.8°C | 96 mm | 79% | 4 m/s | 5.7 |
| 1986 | 14.3°C | 12.4°C | 10.5°C | 18.3°C | 8.1°C | 105 mm | 81% | 3.3 m/s | 6.3 |
| 1985 | 14.4°C | 12.5°C | 10.6°C | 19.2°C | 7.0°C | 93 mm | 81% | 3.1 m/s | 6.3 |
| 1984 | 14.4°C | 12.7°C | 11.0°C | 16.9°C | 9.2°C | 143 mm | 82% | 3.2 m/s | 5.3 |
| 1983 | 12.9°C | 11.2°C | 9.5°C | 17.3°C | 7.7°C | 166 mm | 78% | 4.3 m/s | — |
| 1982 | 12.5°C | 10.8°C | 9.1°C | 17.3°C | 6.8°C | 120 mm | 80% | 4.2 m/s | — |
| 1981 | 14.4°C | 12.6°C | 10.9°C | 18.7°C | 8.5°C | 146 mm | 83% | 3.7 m/s | — |
Actual recorded December data for each year, 1981–2025 — sourced from NASA POWER.
The average high in December is around 13.9°C with lows near 10.2°C (mean 12.1°C), based on 45 years of NASA POWER data.
December averages 110 mm of rainfall in Halfmoon Bay, about average for rainfall. The wettest on record was 189 mm in 2004.
The hottest December reached 20.6°C in 2014. The coldest dipped to 6°C in 1997.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average December temperatures have risen by about 0.5°C. Daytime highs moved from 13.7°C to 14.3°C and overnight lows from 10.2°C to 10.7°C over the same span.
December is one of the warmer months of the year in Halfmoon Bay and about average for rainfall, so plan for around 13.9°C daytime highs and 10.2°C at night.
Not quite — December is the 9th coolest month in Halfmoon Bay, averaging 12.1°C.
For December in Halfmoon Bay, pack light layers you can adjust through the day, with typical highs of 13.9°C and lows of 10.2°C. Bring an umbrella or light rain jacket too.
Relative humidity in December averages 81% — quite humid.
Average wind speed in December is 3.9 m/s. The windiest December on record averaged 5.1 m/s (1990).
The wettest December on record was 2004 with 189 mm. On average, December sees 110 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Halfmoon Bay behaves each December, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for December specifically, along with year-by-year records and how the month has changed over the decades.
