Isahaya climate
Isahaya (Japan) has a humid subtropical climate (Köppen Cfa). The average temperature over the year is 16 °C61 °F, and about 2,078 mm82 in of precipitation falls in an average year.
Temperature by month
Precipitation by month
Isahaya climate table
| Month | High °C°F | Low °C°F | Mean °C°F | Precip. mmin | Frost days |
|---|---|---|---|---|---|
| Jan | 948 | 337 | 643 | 712.8 | 3 |
| Feb | 1152 | 338 | 745 | 993.9 | 2 |
| Mar | 1457 | 642 | 1050 | 1315.2 | 0 |
| Apr | 1966 | 1050 | 1458 | 1676.6 | 0 |
| May | 2374 | 1458 | 1966 | 1867.3 | 0 |
| Jun | 2679 | 1966 | 2272 | 33313 | 0 |
| Jul | 2984 | 2373 | 2679 | 35214 | 0 |
| Aug | 3087 | 2475 | 2781 | 2258.9 | 0 |
| Sep | 2781 | 2068 | 2475 | 2017.9 | 0 |
| Oct | 2272 | 1559 | 1865 | 1174.6 | 0 |
| Nov | 1762 | 1050 | 1356 | 1034.1 | 0 |
| Dec | 1152 | 541 | 847 | 923.6 | 0 |
| Year | 3087 | 337 | 1661 | 2,07882 | 6 |
“Year” row: highest monthly high, lowest monthly low, annual mean and annual total. Frost days are for the whole grid cell.
| Month | Humid. | Cloud | Solar | Daylight |
|---|---|---|---|---|
| Jan | 79% | 69% | 2.4 | 10:12 |
| Feb | 78% | 66% | 3.1 | 10:58 |
| Mar | 77% | 65% | 4.1 | 11:53 |
| Apr | 78% | 65% | 4.9 | 12:57 |
| May | 80% | 69% | 5.2 | 13:50 |
| Jun | 84% | 81% | 4.3 | 14:18 |
| Jul | 86% | 71% | 4.9 | 14:07 |
| Aug | 83% | 62% | 5.2 | 13:21 |
| Sep | 84% | 64% | 4.4 | 12:19 |
| Oct | 81% | 55% | 3.7 | 11:18 |
| Nov | 80% | 58% | 2.8 | 10:25 |
| Dec | 79% | 64% | 2.2 | 9:00 |
Humid. = average relative humidity at 2 m; cloud = average cloud amount; solar = average daily solar energy reaching the ground in kWh/m² (all-sky); daylight in hours:minutes, calculated for the 15th of each month.
What the climate of Isahaya is like
The warmest month is August, with an average high of 30 °C87 °F and a low of 24 °C75 °F. The coldest is January, when highs average 9 °C48 °F and lows 3 °C37 °F. Seasons are strongly marked: the warmest month is on average 21.1 °C38 °F warmer than the coldest.
It is very wet, receiving about 2,078 mm82 in of precipitation per year. The wettest three-month stretch is June–August, which brings 44% of the annual total. The wettest month is July (352 mm14 in), the driest is January (71 mm2.8 in).
Relative humidity ranges from 77% in March to 86% in July. The clearest skies (lowest average cloud amount, 55%) are typical of October. Average wind speed near the ground ranges from 4 km/h (2 mph) in June to 7 km/h (4 mph) in January. Daylight lasts from about 10.0 hours in December to 14.3 hours in June.
Best time to visit Isahaya
Based on these averages, the most comfortable months for sightseeing and outdoor activities are October: average highs of 22 °C72 °F to 22 °C72 °F with 117 mm4.6 in to 117 mm4.6 in of precipitation per month.
The most challenging month is July, which is very wet (352 mm14 in) and humid (86% relative humidity).
Comfort score: months are ranked by how close they come to an average high of 21–28 °C (70–82 °F), lows above 5 °C (41 °F), little precipitation and moderate humidity. The best-ranked months of each place are recommended, even where none meets all of these. These are general rules of thumb applied to long-term averages.
What to pack for Isahaya
- Winter (December–February) — highs 948 to 11 °C52 °F, lows 337 to 5 °C41 °F, about 87 mm3.4 in of precipitation a month. Pack a warm coat, layers and closed shoes.
- Spring (March–May) — highs 1457 to 23 °C74 °F, lows 642 to 14 °C58 °F, about 162 mm6.4 in of precipitation a month. Pack light layers — T-shirts plus a light sweater or jacket and an umbrella or light rain jacket.
- Summer (June–August) — highs 2679 to 30 °C87 °F, lows 1966 to 24 °C75 °F, about 303 mm12 in of precipitation a month. Pack light summer clothes such as T-shirts, shorts or light dresses and a good rain jacket or umbrella and quick-drying shoes.
- Autumn (September–November) — highs 1762 to 27 °C81 °F, lows 1050 to 20 °C68 °F, about 141 mm5.5 in of precipitation a month. Pack light layers — T-shirts plus a light sweater or jacket and an umbrella or light rain jacket.
How Isahaya compares
Compared with Nagasaki, about 18 km to the southwest, Isahaya is on average 0.6 °C1 °F cooler and receives a similar amount of precipitation. The difference is largest in January (0.6 °C1 °F cooler).
Of the 111 places in Japan covered by World Climates, Isahaya is the 31st warmest by annual mean temperature and the 16th wettest by annual precipitation. See all of them on the Japan climate page.
Places in other countries with the most similar temperature and rainfall pattern: Jeju City (South Korea, Cfa), Chongming (China, Cfa) and Ningbo (China, Cfa).
Nearby places
- Nagasaki 18 km · 17 °C62 °F · 2,078 mm82 in
- Ōmuta 44 km · 17 °C62 °F · 2,130 mm84 in
- Sasebo 47 km · 17 °C62 °F · 2,078 mm82 in
- Saga 50 km · 17 °C62 °F · 2,078 mm82 in
- Kumamoto 61 km · 17 °C62 °F · 2,130 mm84 in
- Honmachi 64 km · 17 °C63 °F · 2,326 mm92 in
- Karatsu 67 km · 17 °C63 °F · 1,963 mm77 in
- Fukuoka 91 km · 16 °C61 °F · 1,901 mm75 in
Frequently asked questions
What is the warmest month in Isahaya?
August is the warmest month in Isahaya, with an average high of 30 °C (87 °F) and an average low of 24 °C (75 °F).
What is the coldest month in Isahaya?
January is the coldest month, with an average high of 9 °C (48 °F) and an average low of 3 °C (37 °F).
When does it rain the most in Isahaya?
July is the wettest month with about 352 mm (13.9 in) of precipitation; January is the driest with about 71 mm (2.8 in).
What is the best time to visit Isahaya?
Judging by long-term averages, the most comfortable months are October.
About this data
All figures are 25-year averages (January 2001 – December 2025) from the NASA POWER project. Temperature, humidity, wind and precipitation come from the MERRA-2 reanalysis (precipitation is the bias-corrected MERRA-2 product), cloud and solar values from CERES satellite data. They describe a grid cell of roughly 50–70 km, not a single weather station, so they can differ from airport records — most of all on coasts, in mountains and for rainfall. Average highs and lows are the monthly mean temperature plus/minus half of the average daily temperature range. Counts of rainy days are not part of this dataset.