Altsasu weather in September

In September, Altsasu sees average daytime highs of 21°C and overnight lows near 12°C, with 70 mm of rain across 11.6 wet days and about 12.3 hours of daylight. It is the 3rd-warmest and 10th-wettest month of the year here.

Highs ease over the month, from about 22°C in the first days to 20°C by the end. The sky is clear or mostly clear about 31% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 hours at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is Altsasu's 3rd-clearest and 9th-windiest month. For the whole year in context, see Altsasu's year-round climate.

Daytime high
21°
3rd warmest
Overnight low
12°
9th coldest
Rainfall
70 mm
11.6 wet days
Daylight
12 h 18 min
6:54 AM – 7:12 PM
Cloud cover
56%
3rd clearest
Wind
7 km/h
9th windiest
Solar energy
4.19 kWh/m²
Travel score
6.2
out of 10

Altsasu is municipality of Spain.

Density
276/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 22°C in the first days to 20°C by the end.

A typical September day in Altsasu reaches about 21°C in the afternoon and slips back to 12°C overnight — a 9°C spread between the day's warmth and the night's chill. On most days the high lands between 16°C and 27°C. Set against its neighbours, September runs about 3°C cooler than August and about 3°C warmer than October.

10°15°20°25°30°151015202530
Avg high (°C)Avg low (°C)
12313
22313
32313
42213
52213
62213
72213
82212
92212
102212
112212
122112
132112
142112
152112
162112
172112
182112
192111
202111
212011
222011
232011
242011
252011
262011
272011
282011
292011
302011

How September really feels in Altsasu

Once humidity and wind are folded in, September averages 0 days that feel above 32°C and 0 that feel at or below 0°C — the comfort signal a plain temperature reading hides.

Days feeling ≥ 32°C
0
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

September sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Altsasu weather by month

How September compares with the rest of the year at a glance. September is the 3rd-warmest and 10th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / 11315.13.39.21.5
Feb10° / 10313.6410.22.0
Mar13° / 100142.211.63.2
Apr15° / 113160.613.13.7
May18° / 10615.3014.45.0
Jun21° / 12°7911.6015.16.2
Jul23° / 14°5910.4014.86.9
Aug24° / 14°6511.8013.86.8
Sep21° / 12°7011.6012.36.2
Oct18° / 9612.70.110.85.3
Nov12° / 127150.89.52.8
Dec / 10113.82.28.91.8

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 31% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 16% of September, with mostly cloudy or overcast conditions the remaining 53%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
14852
24852
34852
44852
54951
65050
75050
85050
94951
104951
114951
125050
135050
144951
154951
164753
174753
184555
194555
204555
214555
224654
234654
244555
254555
264555
274555
284357
294357
304456

Chance of precipitation in September

Any precipitation

Altsasu gets around 70 mm of rain over 11.6 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 40% and peaks near 43% on the wettest days.

0%10%20%30%40%50%151015202530
Rain chance (%)
137
237
337
436
537
637
737
837
938
1039
1139
1240
1340
1441
1542
1642
1742
1843
1943
2043
2142
2242
2342
2441
2541
2641
2741
2840
2940
3040

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 52% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)
13442232
23542221
33642211
43842191
53942181
64141171
74241161
84341151
94540141
104639141
114839131
124938120
135038120
145237110
155337100
16553690
17563680
18583570
19583570
20603460
21613450
22613450
23623440
24623440
25643330
26643330
27643330
28653230
29663220
30673120

Wind in September

Winds average 7 km/h in September.

Across September, daily wind ranges from about 7 km/h on the calmest days to 8 km/h at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (km/h)Feels
17calm
27calm
37calm
47calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
147calm
158calm
168calm
178calm
188calm
198calm
208calm
218calm
228calm
238calm
248calm
258calm
268calm
278calm
288calm
298calm
308calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 hours at the start of September to 11 h 36 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 84 minutes over September. Sunrise moves from 6:38 AM to 7:10 AM, and sunset from 7:39 PM to 6:46 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.06:387:39
213.06:397:37
312.96:407:36
412.96:417:34
512.86:427:32
612.86:437:30
712.76:447:28
812.76:457:26
912.66:477:25
1012.66:487:23
1112.56:497:21
1212.56:507:19
1312.46:517:17
1412.46:527:15
1512.36:537:13
1612.36:547:12
1712.26:557:10
1812.26:577:08
1912.16:587:06
2012.16:597:04
2112.07:007:02
2212.07:017:00
2311.97:026:59
2411.97:036:57
2511.87:056:55
2611.87:066:53
2711.77:076:51
2811.77:086:49
2911.67:096:47
3011.67:106:46

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.19 kWh/m².

For context, solar energy here swings from a low near 1.42 kWh/m² to a high of 5.91 kWh/m² in June across the year — September's 4.19 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.7Bright
24.7Bright
34.7Bright
44.6Bright
54.6Bright
64.6Bright
74.5Bright
84.5Bright
94.4Bright
104.4Bright
114.3Bright
124.3Bright
134.3Bright
144.2Bright
154.2Bright
164.1Bright
174.1Bright
184.0Bright
194.0Moderate
203.9Moderate
213.9Moderate
223.9Moderate
233.8Moderate
243.8Moderate
253.8Moderate
263.7Moderate
273.7Moderate
283.6Moderate
293.6Moderate
303.5Moderate
Planning a trip in September

Is September a good time to visit Altsasu?

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

6.2
Sightseeing
3rd-best month of the year
3.9
Beach & pool
3rd-best month of the year

September is a reasonable time to visit Altsasu for sightseeing.

What to pack for Altsasu in September

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

In September, Altsasu sees daytime highs around 21°C and nights near 12°C. Worth packing: rain gear. About 12 days see rain.

rain gear

Sea temperature near Altsasu in September

The nearest coast averages about 21°C 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 53 km away) is warmest in August at about 22°C and coldest in February near 12°C.

It's comfortable for a long swim from Jul 2 to Sep 25 — about 2.8 months when the water holds above 20°C.

10°15°20°25°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmcomfortable to swim
Sea temperature (°C)Comfort
Jan13Bracing
Feb12Bracing
Mar13Bracing
Apr14Bracing
May16Cool
Jun19Cool
Jul21Refreshing
Aug22Refreshing
Sep21Refreshing
Oct18Cool
Nov16Cool
Dec14Bracing

UV index in Altsasu in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 6 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Altsasu peaks around July 15 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 20 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJul 15UV 9Dec 20UV 1
UV index (midday)Level
Jan2Low
Feb2Moderate
Mar5Moderate
Apr6High
May7High
Jun9Very high
Jul9Very high
Aug8Very high
Sep6High
Oct4Moderate
Nov2Low
Dec1Low
Location & terrain

Where is Altsasu?

Altsasu sits at 42.9°N, 2.2°W, 0 m above sea level, in Spain. The nearest listed city is Tolosa, 27 km away.

Topography around Altsasu

How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Altsasu.

Within 3 km, the terrain around Altsasu has large variations in elevation — a maximum elevation change of 625 m around an average of 594 m above sea level; within 16 km, very significant variations in elevation — a maximum elevation change of 1,365 m; within 80 km, very significant variations in elevation — a maximum elevation change of 1,532 m.

The land around Altsasu is covered by trees (66%) and grassland (24%) within 3 km, trees (72%) and grassland (23%) within 16 km, and trees (44%) and cropland (22%) within 80 km.

3 km
625 m
16 km
1,365 m
80 km
1,532 m
treesshrubsgrasslandcroplandartificial surfaceswater
September weather nearby: Tolosa 27 km · Arrasate / Mondragón 32 km · Eibar 40 km · Barañáin 41 km · Oria 41 km · Gasteiz / Vitoria 42 km · Ermitagaña 42 km · Ermua 42 km

Spain travel facts

Travel advisory
Level 2
Exercise Increased Caution
Power plugs
Type C / F
230 V · 50 Hz
Prices
≈ 65% of US
price level, 2025
GDP per capita
$38,627
2025
Happiness
6.5 / 10
World Happiness, 2025
Safe drinking water
99%
of population, 2024
Homicide rate
0.7
per 100k, 2023
Road deaths
3.9
per 100k/yr, 2019
Income group
High
World Bank
English
Moderate
EF EPI 540
Religion
Roman Catholic 58%atheist 16%agnostic 11%non-believer 11%

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 Altsasu (42.9°, -2.1652°, elevation 0 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. 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. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).