The southwest (summer) monsoon drives the wet season across much of South and Southeast Asia. In India it normally sets in over Kerala around 1 June and covers the entire country around 8 July.[1] It withdraws from the whole country around 15 October.[2] Thailand's weather service dates the rainy season, driven by the southwest monsoon, from about mid-May to mid-October.[3]
When the southwest monsoon retreats, the northeast monsoon takes over and some coasts turn wet. October to December is the chief rainy season in Tamil Nadu, which receives 48% of its annual rain in these three months.[4] On the Gulf side of southern Thailand, normal rainfall is 254 mm in October and 361 mm in November, against 147 mm in September.[3] The east coast of Peninsular Malaysia gets the most rain from November to January, while June and July are the driest months in most districts.[5] For central Vietnam, the national forecasting centre treats October and November as the main rainy months from Ha Tinh to Hue and along the south central coast.[6] Sri Lanka's weather service splits the year into four seasons: the first inter-monsoon (March to April), the southwest monsoon (May to September), the second inter-monsoon (October to November) and the northeast monsoon (December to February).[7]
Indonesia sits between two monsoon systems. Its weather agency links the rainy season to the west monsoon from Asia and the dry season to the east monsoon from Australia, and the seasons do not start at the same time everywhere.[8] Where the rain follows the monsoon pattern, it peaks from December to February and the driest months are June to August; near the equator there are two peaks, around March and October.[9]
In the Philippines, the southwest monsoon (Habagat) brings rain to the western side of the country from May to September, while the northeast monsoon (Amihan) brings cold winds and rain to the east.[10] Typhoons peak from July to October, when nearly 70% of them develop.[11]
In Japan and Korea the early summer rains come with a stationary front. Japan's rainy season (Baiu or tsuyu) lasts from early June to late July everywhere except Hokkaido; around Tokyo it normally runs from about 7 June to about 19 July.[12] Korea's changma lasts on average from 25 June to 26 July in the central region.[13] Typhoons form most often later in the summer: in the western North Pacific, an average of 5.7 tropical storms or typhoons form in August and 5.0 in September, more than in any other month.[14]
On the map, the rain and typhoon layers show these shifts month by month for each place.
The climate values are averages for 1991 to 2020 from TerraClimate, a global climate data set with a grid of about 4 km. For each place the map uses the nearest grid cell on land. Temperatures are the average daily high and low, rain is the average total per month.
For tropical storms the map counts, for each month, in how many of the 30 seasons from 1995 to 2024 a tropical storm, typhoon or cyclone with winds of at least 34 knots passed within 200 km. The tracks come from NOAA's IBTrACS archive.
Every month starts with zero points. Rain adds 1 point above 130 mm, 2 points above 220 mm and 3 points above 350 mm. A daytime high of 34.5 °C or more adds 1 point, 37 °C 2 points and 40 °C 3 points. A daytime high below 11 °C adds 1 point, below 3 °C 2 points and below -5 °C 3 points. Tropical storms add 1 point if one came close in at least 20 % of the years and 2 points from 50 %. Fine particles (PM2.5) add 1 point from a typical monthly mean of 55 µg/m³ and 2 points from 125 µg/m³, where the US air quality index starts to call the air unhealthy and very unhealthy; from 35 µg/m³ the place is marked as unhealthy for sensitive groups, without points. 0 points means great, 1 good, 2 mixed, 3 or more poor.
Air quality comes from SatPM2.5, monthly estimates of fine particles (PM2.5) on a grid of about 11 km that combine satellite measurements with a chemical transport model and are calibrated to ground monitors. For each month the map shows the median of the 10 years from 2015 to 2024, so a single year with heavy smoke haze does not set the value. How often the monthly mean reached 55 µg/m³ is shown separately for each place.
Tropical rain often falls in short, heavy showers, so a wet month can still have plenty of sunshine. Humidity, sea conditions and festivals are not part of the rating. PM2.5 is a monthly mean: on single days, especially during fires, the air can be far worse. In the mountains and on small islands, the 4 km grid can differ from the weather in town.
