Karatsu weather in September

In September, Karatsu sees average daytime highs of 26°C and overnight lows near 22°C, with 179 mm of rain across 12.6 wet days and about 12.2 hours of daylight. It is the 3rd-warmest and 3rd-wettest month of the year here.

Highs ease over the month, from about 28°C in the first days to 25°C by the end. The sky is clear or mostly clear about 36% of the time in September, and the air most often feels oppressive.

Daylight stretches from about 12 h 42 min at the start of September to 11 h 42 min by month's end. Set against the rest of the year, September is Karatsu's 3rd-clearest and 7th-windiest month. For the whole year in context, see Karatsu's year-round climate.

Daytime high
26°
3rd warmest
Overnight low
22°
10th coldest
Rainfall
179 mm
12.6 wet days
Daylight
12 h 12 min
6:08 AM – 6:21 PM
Cloud cover
58%
3rd clearest
Wind
14 km/h
7th windiest
Solar energy
4.2 kWh/m²
Travel score
6.2
out of 10

Karatsu is city in Saga Prefecture, Japan.

Density
241/km²
people per km²
Founded
2005

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 28°C in the first days to 25°C by the end.

A typical September day in Karatsu reaches about 26°C in the afternoon and slips back to 22°C overnight — a 4°C spread between the day's warmth and the night's chill. On most days the high lands between 24°C and 29°C. Set against its neighbours, September runs about 3°C cooler than August and about 4°C warmer than October.

15°20°25°30°35°151015202530
Avg high (°C)Avg low (°C)
12824
22824
32824
42824
52824
62824
72824
82724
92723
102723
112723
122723
132723
142723
152623
162622
172622
182622
192622
202622
212622
222522
232521
242521
252521
262521
272521
282521
292421
302420

How September really feels in Karatsu

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.

Karatsu weather by month

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

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / 7711.81.2101.9
Feb10° / 7810.30.810.82.2
Mar13° / 12411.60.211.73.5
Apr17° / 12°13411012.85.3
May21° / 16°14310.3013.76.4
Jun24° / 20°27714.7014.25.8
Jul28° / 24°26015.40145.1
Aug29° / 26°16213.7013.24.9
Sep26° / 22°17912.6012.26.2
Oct22° / 18°1038.1011.27.1
Nov17° / 13°959.3010.35.5
Dec12° / 8111.10.39.83.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 36% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 15% of September, with mostly cloudy or overcast conditions the remaining 49%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
14951
24951
35050
45050
55050
65050
75149
85149
95149
105149
115248
125248
135149
145149
155149
165149
175149
185149
195050
205050
215050
225050
235050
245149
255149
265149
275248
285248
295248
305446

Chance of precipitation in September

Any precipitation

Karatsu gets around 179 mm of rain over 12.6 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 41% and peaks near 47% on the wettest days. The odds ease toward the end of the month.

0%20%40%60%151015202530
Rain chance (%)
147
246
346
446
546
645
745
845
945
1044
1144
1243
1343
1442
1542
1641
1741
1840
1940
2039
2139
2238
2338
2437
2537
2636
2735
2835
2934
3033

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the oppressive band about 33% of days. Sticky, muggy-or-worse air turns up on roughly 70% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)Miserable (%)
1004225123
2005245021
3006255019
4006265117
5017274916
6018284815
7019294713
80111304612
90212304511
100213314410
11031431429
12131532418
13141732398
14151832377
15161932357
16272032336
17282232315
18292332295
193102431275
203112531264
213122631244
224132730223
234142830213
245152930193
255162929182
266183028162
277193028152
287203027142
298213127121
309233025111

Wind in September

Winds average 14 km/h in September.

Across September, daily wind ranges from about 13 km/h on the calmest days to 14 km/h at its breeziest. It stays fairly steady from day to day.

05101520151015202530
Wind speed (km/h)Feels
113light breeze
213light breeze
313light breeze
413light breeze
513light breeze
613light breeze
713light breeze
813light breeze
913light breeze
1013light breeze
1113light breeze
1214light breeze
1314light breeze
1414light breeze
1514light breeze
1614light breeze
1714light breeze
1814light breeze
1914light breeze
2014light breeze
2114light breeze
2214light breeze
2314light breeze
2414light breeze
2514light breeze
2614light breeze
2714light breeze
2814light breeze
2914light breeze
3014light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 42 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 60 minutes over September. Sunrise moves from 5:58 AM to 6:18 AM, and sunset from 6:42 PM to 6:01 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.75:586:42
212.75:596:40
312.75:596:39
412.66:006:38
512.66:016:36
612.66:016:35
712.56:026:33
812.56:036:32
912.56:046:31
1012.46:046:29
1112.46:056:28
1212.36:066:26
1312.36:066:25
1412.36:076:23
1512.26:086:22
1612.26:086:21
1712.26:096:19
1812.16:106:18
1912.16:106:16
2012.16:116:15
2112.06:126:13
2212.06:126:12
2312.06:136:11
2411.96:146:09
2511.96:156:08
2611.86:156:06
2711.86:166:05
2811.86:176:03
2911.76:176:02
3011.76:186:01

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.2 kWh/m².

For context, solar energy here swings from a low near 2.14 kWh/m² to a high of 5.41 kWh/m² in May across the year — September's 4.2 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.5Bright
24.5Bright
34.5Bright
44.5Bright
54.4Bright
64.4Bright
74.4Bright
84.4Bright
94.4Bright
104.3Bright
114.3Bright
124.3Bright
134.3Bright
144.3Bright
154.2Bright
164.2Bright
174.2Bright
184.2Bright
194.2Bright
204.1Bright
214.1Bright
224.1Bright
234.1Bright
244.0Bright
254.0Bright
264.0Bright
274.0Moderate
284.0Moderate
294.0Moderate
303.9Moderate
Planning a trip in September

Hazard calendar for Karatsu

In seasonPeak

In September, Karatsu sits inside its pacific typhoon and rainy season season. The full year is below, with each hazard's peak months called out.

Karatsu sits in the Pacific typhoon belt; the season peaks July–October.

Karatsu's rainy season runs April–September, when most of the year's rain falls.

Pacific typhoon
Rainy season
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is September a good time to visit Karatsu?

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
6.1
Beach & pool
2nd-best month of the year

September is a reasonable time to visit Karatsu for sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Karatsu in September

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

In September, Karatsu sees daytime highs around 26°C and nights near 22°C. Worth packing: light clothes and rain gear. About 13 days see rain.

light clothesrain gear

Sea temperature near Karatsu in September

The nearest coast averages about 25°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 22 km away) is warmest in August at about 27°C and coldest in February near 14°C.

It's comfortable for a long swim from Jun 8 to Nov 21 — about 5.5 months when the water holds above 20°C.

15°20°25°30°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmtropicalcomfortable to swim
Sea temperature (°C)Comfort
Jan16Cool
Feb14Bracing
Mar14Bracing
Apr16Cool
May18Cool
Jun21Refreshing
Jul24Warm
Aug27Warm
Sep25Warm
Oct23Refreshing
Nov21Refreshing
Dec18Cool

UV index in Karatsu in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 9 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Karatsu peaks around July 23 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 22 at about 3 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 10 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highModerateJul 23UV 9Dec 22UV 3
UV index (midday)Level
Jan3Moderate
Feb4Moderate
Mar6High
Apr8Very high
May8Very high
Jun7Very high
Jul9Very high
Aug9Very high
Sep9Very high
Oct6High
Nov4Moderate
Dec3Moderate

Air quality in Karatsu 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 Karatsu is worst in April — around 24 µg/m³ PM2.5 (moderate), about 2.2× the cleanest month (July, 11 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateApr 924 µg/m³Jul 2211 µg/m³
PM2.5 (µg/m³)Level
Jan17Moderate
Feb20Moderate
Mar24Moderate
Apr24Moderate
May21Moderate
Jun16Moderate
Jul11Good
Aug11Good
Sep12Good
Oct11Good
Nov14Moderate
Dec13Moderate
Location & terrain

Where is Karatsu?

Karatsu sits at 33.4°N, 130.0°E, 7 m above sea level, in Japan. The nearest listed city is Imarichō-kō, 21 km away.

Topography around Karatsu

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

Within 3 km, the terrain around Karatsu has only modest variations in elevation — a maximum elevation change of 218 m around an average of 38 m above sea level; within 16 km, large variations in elevation — a maximum elevation change of 899 m; within 80 km, very significant variations in elevation — a maximum elevation change of 1,318 m.

The land around Karatsu is covered by trees (41%), artificial surfaces (28%) and water (24%) within 3 km, trees (59%) and water (29%) within 16 km, and water (58%) and trees (29%) within 80 km.

3 km
218 m
16 km
899 m
80 km
1,318 m
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Imarichō-kō 21 km · Taku 23 km · Itoshima 23 km · Maebaru-chūō 25 km · Ogi 28 km · Matsuura 28 km · Takeo 28 km · Arita 30 km

Japan travel facts

Travel advisory
Level 1
Exercise Normal Precautions
Power plugs
Type A / B
100 V · 50 / 60 Hz
Prices
≈ 65% of US
price level, 2025
GDP per capita
$35,951
2025
Happiness
6.1 / 10
World Happiness, 2025
Safe drinking water
99%
of population, 2024
Homicide rate
0.2
per 100k, 2023
Road deaths
3.6
per 100k/yr, 2019
Income group
High
World Bank
English
Very low
EF EPI 446
Religion
Shintoism 49%Buddhism 46%other 4%Christianity 1%

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 Karatsu (33.4425°, 129.9697°, elevation 7 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. Tropical-cyclone seasons are the published climatological basin seasons (NOAA National Hurricane Center / regional warning centres). 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).