Castle Hill in Summer
In summer (December, January and February), Castle Hill sees average daytime highs around 27°C and overnight lows near 18°C, with 207 mm of rain over about 28 wet days across the season. It is the warmest season of the year and the wettest season of the year.
Across summer, daytime highs hold fairly steady around 27°C. The sky is clear or mostly clear about 33% of the time across summer, and the air most often feels humid.
Summer is Castle Hill's weakest season of the year to visit on our travel score. For the whole year in context, see Castle Hill's year-round climate.
- Avg daytime high
- 27°C
- warmest season of the year
- Avg overnight low
- 18°C
- Rainfall
- 207 mm
- 28 wet days
- Avg wind
- 11 km/h
- Travel score
- 6.4
- weakest season of the year
- Months
- Dec · Jan · Feb
Temperature in Castle Hill in Summer
Across summer, daytime highs hold fairly steady around 27°C.
A typical summer day in Castle Hill reaches about 27°C and drops to 18°C overnight. The warmest of the three months is January, the coolest December.
Castle Hill weather by month
How the three summer months (December, January and February) compare with the rest of the year — the season's months are highlighted.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|
| Jan | 28° / 19° | 66 | 9.1 | 14 | 6.2 |
| Feb | 27° / 19° | 84 | 10 | 13.3 | 6.3 |
| Mar | 26° / 17° | 66 | 10.6 | 12.3 | 6.8 |
| Apr | 23° / 13° | 51 | 7.8 | 11.2 | 7.4 |
| May | 20° / 10° | 45 | 6.3 | 10.3 | 7.1 |
| Jun | 18° / 8° | 61 | 7.4 | 9.8 | 6.3 |
| Jul | 17° / 7° | 35 | 5.7 | 10 | 6.5 |
| Aug | 19° / 7° | 35 | 5.2 | 10.7 | 7.2 |
| Sep | 22° / 10° | 39 | 6.1 | 11.8 | 7.5 |
| Oct | 24° / 13° | 49 | 7.3 | 12.8 | 7.5 |
| Nov | 25° / 15° | 66 | 8.6 | 13.8 | 7.0 |
| Dec | 27° / 17° | 58 | 8.7 | 14.2 | 6.7 |
Cloud cover in Summer
The sky is clear or mostly clear about 33% of the time across summer.
Chance of precipitation in Summer
Castle Hill gets around 207 mm of rain over 28 wet days across summer. The line is the day-by-day chance of measurable precipitation.
Humidity in Summer
Most of summer feels humid — the stacked bands show each day's mix of comfort levels, read off the dew point.
Wind in Summer
Winds average 11 km/h across summer.
Sunrise & sunset in Summer
Daylight runs from about 14 h 06 min in early December to 12 h 48 min by late February. The lit band spans sunrise to sunset each day.
Solar energy in Summer
Average shortwave solar energy reaching the ground each day across summer, about 6.2 kWh/m².
Hazard calendar for Castle Hill
In summer, Castle Hill overlaps its cyclone season. The full year is below, with each hazard's peak months called out.
Castle Hill sits in the South Indian Ocean cyclone belt; the season peaks January–March.
Is summer a good time to visit Castle Hill?
Our two travel scores rate summer for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal), averaged across the three months.
summer is a reasonable time to visit Castle Hill for sightseeing. The water and warmth also suit a beach or pool day.
What to pack for Castle Hill in Summer
From summer's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In summer, Castle Hill sees daytime highs around 27°C and nights near 18°C. Pack light clothes and sun protection. Worth having: rain gear. About 28 days see rain.
Sea temperature near Castle Hill in Summer
The nearest coast averages about 22°C across summer — the other half of the beach question. The full-year curve and swim-comfort zones are below.
The sea at the nearest coast (about 37 km away) is warmest in February at about 23°C and coldest in August near 18°C.
It's comfortable for a long swim from Nov 16 to Jun 4 — about 6.6 months when the water holds above 20°C.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 23 | 23 | 23 | 22 | 21 | 20 | 19 | 18 | 18 | 19 | 20 | 21 |
| Comfort | Refreshing | Refreshing | Refreshing | Refreshing | Refreshing | Cool | Cool | Cool | Cool | Cool | Refreshing | Refreshing |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 23 | Refreshing |
| Feb | 23 | Refreshing |
| Mar | 23 | Refreshing |
| Apr | 22 | Refreshing |
| May | 21 | Refreshing |
| Jun | 20 | Cool |
| Jul | 19 | Cool |
| Aug | 18 | Cool |
| Sep | 18 | Cool |
| Oct | 19 | Cool |
| Nov | 20 | Refreshing |
| Dec | 21 | Refreshing |
UV index in Castle Hill in Summer
Clear-sky midday UV across summer averages around 12 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.
Under clear skies, the midday UV index in Castle Hill peaks around January 16 at about 12 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near June 19 at about 2 (moderate).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 10 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 12 | 11 | 9 | 6 | 4 | 2 | 3 | 4 | 6 | 8 | 10 | 12 |
| Level | Extreme | Extreme | Very high | High | Moderate | Moderate | Moderate | Moderate | High | Very high | Very high | Extreme |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 12 | Extreme |
| Feb | 11 | Extreme |
| Mar | 9 | Very high |
| Apr | 6 | High |
| May | 4 | Moderate |
| Jun | 2 | Moderate |
| Jul | 3 | Moderate |
| Aug | 4 | Moderate |
| Sep | 6 | High |
| Oct | 8 | Very high |
| Nov | 10 | Very high |
| Dec | 12 | Extreme |
Air quality in Castle Hill in Summer
Average fine-particle pollution (PM2.5) through the year — so you can see where summer falls, not just the annual average.
Air quality in Castle Hill is worst in December — around 49 µg/m³ PM2.5 (poor), about 8.1× the cleanest month (June, 6 µg/m³).
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 11 | 7 | 7 | 8 | 8 | 6 | 6 | 8 | 10 | 10 | 25 | 49 |
| Level | Good | Good | Good | Good | Good | Good | Good | Good | Good | Good | Moderate | Poor |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 11 | Good |
| Feb | 7 | Good |
| Mar | 7 | Good |
| Apr | 8 | Good |
| May | 8 | Good |
| Jun | 6 | Good |
| Jul | 6 | Good |
| Aug | 8 | Good |
| Sep | 10 | Good |
| Oct | 10 | Good |
| Nov | 25 | Moderate |
| Dec | 49 | Poor |
Where is Castle Hill?
Castle Hill sits at 33.7°S, 151.0°E, 126 m above sea level, in Australia. The nearest listed city is Baulkham Hills, 3.0 km away.
Topography around Castle Hill
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Castle Hill.
Within 3 km, the terrain around Castle Hill has only modest variations in elevation — a maximum elevation change of 139 m around an average of 118 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 251 m; within 80 km, large variations in elevation — a maximum elevation change of 1,191 m.
The land around Castle Hill is covered by trees (64%) and artificial surfaces (31%) within 3 km, trees (55%) and artificial surfaces (32%) within 16 km, and trees (61%) and water (26%) within 80 km.
Australia travel facts
- Travel advisory
- Level 1
- Exercise Normal Precautions
- Power plugs
- Type I
- 230 V · 50 Hz
- Prices
- ≈ 90% of US
- price level, 2025
- GDP per capita
- $65,130
- 2025
- Happiness
- 6.9 / 10
- World Happiness, 2025
- Homicide rate
- 0.9
- per 100k, 2023
- Road deaths
- 4.9
- per 100k/yr, 2019
- Income group
- High
- World Bank
- Religion
Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Castle Hill (-33.7333°, 151°, elevation 126 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google.