Castaic weather in September

In September, Castaic sees average daytime highs of 85°F and overnight lows near 61°F, with 0.2 in of rain across 0.7 wet days and about 12.2 hours of daylight. It is the 3rd-warmest and 9th-wettest month of the year here.

Highs ease over the month, from about 88°F in the first days to 82°F by the end. The sky is clear or mostly clear about 86% of the time in September, and the air most often feels dry.

Daylight stretches from about 12 h 48 min at the start of September to 11 h 42 min by month's end. Set against the rest of the year, September is Castaic's 2nd-clearest and 12th-windiest month. For the whole year in context, see Castaic's year-round climate.

Daytime high
85°
3rd warmest
Overnight low
61°
10th coldest
Rainfall
0.2 in
0.7 wet days
Daylight
12 h 12 min
5:42 AM – 5:55 PM
Cloud cover
14%
2nd clearest
Wind
4 mph
12th windiest
Solar energy
6.34 kWh/m²
Travel score
7.2
out of 10

Castaic is census-designated place in Los Angeles County, California, United States.

Density
1,009/km²
people per km²

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 88°F in the first days to 82°F by the end.

A typical September day in Castaic reaches about 85°F in the afternoon and slips back to 61°F overnight — a 24°F spread between the day's warmth and the night's chill. On most days the high lands between 76°F and 94°F. Set against its neighbours, September runs about 4°F cooler than August and about 8°F warmer than October.

60°80°100°151015202530
Avg high (°F)Avg low (°F)
18864
28864
38864
48764
58764
68764
78763
88763
98663
108662
118662
128562
138562
148561
158561
168561
178561
188460
198460
208460
218460
228460
238360
248359
258359
268359
278359
288258
298258
308258

Castaic weather by month

How September compares with the rest of the year at a glance. September is the 3rd-warmest and 9th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysDaylight (hours)Travel score
Jan60° / 41°2.85.7105.3
Feb61° / 42°3.2710.75.5
Mar65° / 44°2.2611.76.7
Apr70° / 48°0.83.512.87.9
May76° / 53°0.42.113.88.8
Jun82° / 59°0.10.414.38.2
Jul87° / 64°0.10.814.16.3
Aug89° / 65°0.00.213.35.9
Sep85° / 61°0.20.712.27.2
Oct77° / 54°0.62.511.18.7
Nov67° / 46°0.7310.27.6
Dec59° / 40°2.05.29.75.3

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 86% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 7% of September, with mostly cloudy or overcast conditions the remaining 7%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
1946
2946
3946
4946
5946
6946
7946
8946
9946
10946
11946
12946
13946
14946
15937
16937
17937
18937
19937
20937
21937
22937
23919
24919
25919
26919
27919
28919
299010
309010

Chance of precipitation in September

Any precipitation

Castaic gets around 0.2 in of rain over 0.7 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 3% and peaks near 4% on the wettest days.

0%10%20%30%151015202530
Rain chance (%)
12
22
32
42
52
62
72
82
92
102
112
122
132
142
152
162
172
182
193
203
213
223
233
243
253
263
274
284
294
304

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

Most of September feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, September lands in the dry band about 79% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)
168257
268257
369247
470237
570237
672226
772226
873216
974215
1075205
1176204
1277194
1378193
1478193
1580182
1680182
1781172
1881172
1982162
2082162
2183152
2283152
2383152
2485141
2585141
2686131
2787121
2887121
2988111
3088111

Wind in September

Winds average 4 mph in September, the calmest month.

Across September, daily wind ranges from about 4 mph on the calmest days to 4 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
14calm
24calm
34calm
44calm
54calm
64calm
74calm
84calm
94calm
104calm
114calm
124calm
134calm
144calm
154calm
164calm
174calm
184calm
194calm
204calm
214calm
224calm
234calm
244calm
254calm
264calm
274calm
284calm
294calm
304calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 48 min at the start of September to 11 h 42 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 66 minutes over September. Sunrise moves from 5:31 AM to 5:53 AM, and sunset from 6:17 PM to 5:35 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.85:316:17
212.75:326:16
312.75:336:14
412.65:346:13
512.65:346:11
612.65:356:10
712.55:366:08
812.55:376:07
912.55:376:05
1012.45:386:04
1112.45:396:03
1212.45:406:01
1312.35:406:00
1412.35:415:58
1512.25:425:57
1612.25:425:55
1712.25:435:54
1812.15:445:52
1912.15:455:51
2012.15:455:49
2112.05:465:48
2212.05:475:46
2312.05:485:45
2411.95:485:43
2511.95:495:42
2611.85:505:40
2711.85:515:39
2811.85:515:38
2911.75:525:36
3011.75:535:35

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 6.34 kWh/m².

For context, solar energy here swings from a low near 2.98 kWh/m² to a high of 8.34 kWh/m² in June across the year — September's 6.34 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
16.9Intense
26.9Intense
36.8Intense
46.8Intense
56.8Intense
66.7Intense
76.7Intense
86.7Intense
96.6Intense
106.6Intense
116.5Intense
126.5Intense
136.5Intense
146.4Intense
156.4Intense
166.3Intense
176.3Intense
186.3Intense
196.2Intense
206.2Intense
216.1Intense
226.1Intense
236.0Intense
246.0Bright
255.9Bright
265.9Bright
275.8Bright
285.8Bright
295.7Bright
305.7Bright
Planning a trip in September

Is September a good time to visit Castaic?

Our two travel scores rate September for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

7.2
Sightseeing
6th-best month of the year
9.1
Beach & pool
1st-best month of the year

September is one of the better times to visit Castaic for general sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Castaic in September

From September's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In September, Castaic sees daytime highs around 85°F and nights near 61°F. Pack light clothes and sun protection.

light clothessun protection

Sea temperature near Castaic in September

The nearest coast averages about 67°F in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 38 mi away) is warmest in August at about 67°F and coldest in March near 58°F.

The water stays below 68°F all year — cool enough that most swimmers want a wetsuit.

55°60°65°70°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshing
Sea temperature (°F)Comfort
Jan58Bracing
Feb58Bracing
Mar58Bracing
Apr58Bracing
May60Cool
Jun63Cool
Jul66Cool
Aug67Cool
Sep67Cool
Oct65Cool
Nov62Cool
Dec60Cool

UV index in Castaic in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 8 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Castaic peaks around June 23 at about 11 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 15 at about 3 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 11 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highExtremeVery highHighModerateJun 23UV 11Dec 15UV 3
UV index (midday)Level
Jan4Moderate
Feb5Moderate
Mar5Moderate
Apr8Very high
May8Very high
Jun11Extreme
Jul11Extreme
Aug11Extreme
Sep8Very high
Oct6High
Nov3Moderate
Dec3Moderate

Air quality in Castaic in September

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where September falls, not just the annual average.

Air quality in Castaic is worst in December — around 29 µg/m³ PM2.5 (moderate), about 2.4× the cleanest month (May, 12 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateDec 1428 µg/m³May 1812 µg/m³
PM2.5 (µg/m³)Level
Jan18Moderate
Feb17Moderate
Mar17Moderate
Apr15Moderate
May12Good
Jun14Moderate
Jul25Moderate
Aug26Moderate
Sep24Moderate
Oct18Moderate
Nov23Moderate
Dec29Moderate
Location & terrain

Where is Castaic?

Castaic sits at 34.5°N, 118.6°W, 1,227 ft above sea level, in United States. The nearest listed city is Valencia, 3.1 mi away.

Topography around Castaic

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Castaic.

Within 2 miles, the terrain around Castaic has significant variations in elevation — a maximum elevation change of 1,043 ft around an average of 1,401 ft above sea level; within 10 miles, large variations in elevation — a maximum elevation change of 3,425 ft; within 50 miles, extreme variations in elevation — a maximum elevation change of 9,318 ft.

The land around Castaic is covered by grassland (41%) and shrubs (26%) within 2 miles, shrubs (35%) and grassland (35%) within 10 miles, and grassland (35%) within 50 miles.

2 miles
1,043 ft
10 miles
3,425 ft
50 miles
9,318 ft
treesshrubsgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Valencia 3.1 mi · Stevenson Ranch 7.5 mi · Santa Clarita 8.1 mi · Canyon Country 9.9 mi · Sylmar 16 mi · Chatsworth 16 mi · Simi Valley 17 mi · San Fernando 18 mi

United States travel facts

Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 100% of US
price level, 2025
GDP per capita
$90,027
2025
Happiness
6.8 / 10
World Happiness, 2025
Safe drinking water
98%
of population, 2024
Homicide rate
5.8
per 100k, 2023
Road deaths
12.7
per 100k/yr, 2019
Income group
High
World Bank
Religion
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 2%

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 Castaic (34.4889°, -118.6229°, elevation 1,227 ft), 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. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).