Taiwan's plum rain season (梅雨季) runs from May to June each year. The current page of the Central Weather Administration (CWA) climate portal also compiles rainfall for the "plum rain season (May-June)", and the CWA's 2020 edition of its meteorology Q&A booklet (氣象常識問答集) explains that this is a fixed period set in 1994 for disaster-prevention outreach, not an "onset" or "end" of plum rain (入梅、出梅) announced each year according to the weather. In climate terms, the notable rain from the plum rain front mostly falls from mid-May to mid-June; after mid-to-late June the weather turns to mainly afternoon thunderstorms, and the typhoon season does not start until mid-August; but it varies a great deal from year to year.
This article sets out how the CWA defines the plum rain season, the yearly statistics, and how it differs from the typhoon season, and ends with a home preparation checklist that points to existing articles on this site for the details. To see whether the next few days suit drying laundry, use Is today good for laundry, airing quilts or washing the car?; during extremely heavy rain, see Real-time flood reports and heavy-rain warning dashboard.
How the CWA defines the plum rain season
The CWA's Q&A booklet explains that plum rain is a weather and climate phenomenon unique to East Asia, occurring in late spring and early summer over Japan, Taiwan and southern China. When the winter northeast monsoon and the summer southwest monsoon alternate, the two airflows meet and form a nearly stationary plum rain front, causing continuous or intermittent rain, sometimes with heavy rain. Because the precipitation is mostly persistent, the air is humid and things easily go moldy, it is also called "mold rain" (霉雨).
The same booklet states that Taiwan's plum rain period occurs from May to June, Japan's lags by about half a month, and the middle and lower Yangtze lags by about 1 month; because atmospheric circulation differs from year to year, the plum rain period varies greatly. The Central Weather Bureau (中央氣象局) therefore set May to June of each year as Taiwan's plum rain season starting in 1994, to coordinate with the relevant agencies in stepping up disaster-prevention outreach (this comes from the March 2020 edition of the booklet; this article did not find a newer edition; for the current wording of May to June, see the climate portal below). The booklet also notes that how to define clearly the start and end of a season is still a scientific question awaiting research.
This article infers that when the news says "this year's plum rain season has begun," it usually means the plum rain front has arrived; this article did not find any CWA announcement or operating rule that declares an onset date or end date of plum rain (入梅日、出梅日).
Where mid-May to mid-June comes from
The CWA climate portal divides late spring through summer into four stages, summarized below.
| Time (climate average) | Stage | Weather characteristics | Basis |
|---|
| Before mid-May | Before plum rain starts | The Pacific high-pressure ridge covers the South China Sea area, and there is often a hot period | CWA climate portal |
| Mid-May to mid-June | Taiwan plum rain | The northeast wind and the southwest monsoon face off near Taiwan, forming a slow-moving or nearly stationary front that brings notable rain | Same as above |
| After mid-to-late June | East Asian plum rain | The subtropical high strengthens and extends west, Taiwan's weather settles, with mainly afternoon thunderstorms; the front moves north and affects the Yangtze basin and Japan | Same as above |
| Mid-August | Typhoon season | The subtropical high jumps north to Japan, the monsoon trough dominates the western North Pacific, and the typhoon season begins | Same as above |
The portal also looks at the seasonal change through the "onset of the summer monsoon": the statistical average date is around the 28th pentad (候) (May 16 to 20), the normal range is about May 11 to 25, and there is no obvious long-term trend from year to year. The portal also explains that the timing of the monsoon onset and the timing of actual rain in Taiwan are close in about 65% of years, and in some years the rain comes earlier or later than the monsoon onset.
How much rain, and how it differs from typhoon season
Plum rain season rainfall differs every year. The CWA climate portal says that in the plum rain season (May to June) the average rainfall at 11 lowland stations in Taiwan is about 440.7 mm; the highest since 1951 was 891.1 mm in 2012 and the lowest was 193.4 mm in 1980. Terrain also matters a lot: the windward western side gets far more rain than the east, and heavy-rain frequency in the plum rain season in the west is about 2 to 4 times that of the east.
The Q&A booklet describes two sides of plum rain: plum rain season rainfall averages about 1/4 of the annual total and is the most effective way to end the spring drought, and a dry or missing plum rain season (乾梅、空梅) can lead to drought; on the other hand, heavy rain in the plum rain season has also caused several major floods. The booklet's statistics for direct property losses from weather causes from 1985 to 2017 show about 82% from typhoons and a little over 12% (12.3%) from plum rain; typhoons and plum rain are Taiwan's two most serious weather disasters.
Compared with the typhoon season, plum rain is characterized by continuous or intermittent rain from the stationary front, and by strong convection near the front. A CWA press release forwarded by the Ministry of Transportation and Communications in April 2026 warns that in recent years total plum rain season rainfall has not clearly increased or decreased, but rainfall is more concentrated in time and short bursts of intense rain are more frequent; plum rain fronts also often come with lightning, so guard against lightning strikes and strong gusts. For what to do when you receive a short-term heavy-rain alert, see What is a severe thunderstorm nowcast message? and How are heavy rain and extremely heavy rain classified?.
Home moisture-prevention checklist
The checklist below is compiled by this article, ordered as "keep water out first, drain it second, dehumidify last." Each item already has an article on this site, so only the key points are listed here.
- Drainage: before May, clear the drain holes and downspout heads of balconies, rooftops and awnings; in the rainy season, water that cannot drain in time easily backs up over the threshold. The CWA press release also calls on everyone to dredge drainage systems early. For pipe diameter and slope problems, see Balcony and rooftop drainage upgrades.
- Window frames and exterior walls: after days of rain, check whether water marks or wall efflorescence and peeling (壁癌) have spread at the bottom edge of window frames and at wall corners. To judge whether it is a leak, see How to deal with wall leaks in the plum rain season; for water seeping around window frames, see Testing and fixing window frames that leak in the rain.
- Dehumidifying: put out a hygrometer first, so you know the actual humidity at home before deciding how long to run the dehumidifier; for target levels, see What indoor humidity counts as damp. For where to place the dehumidifier and whether it can be used to dry clothes, see the article under laundry below.
- Appliances: for appliance care and breakdown prevention in humid seasons, see Protecting appliances from moisture in the plum rain season; this article does not repeat it.
- Laundry: if clothes will not dry after days of rain, see Drying laundry indoors on rainy days: dehumidifiers and dryers.
- Low floors: if your home has flooded or had drainage back up before, confirm before the rainy season where the flood barriers and sandbags are kept, and take them out when an extremely heavy rain advisory (豪雨特報) is issued.
What not to do yourself
Climbing onto the roof, an awning or an exterior wall in the rain to clear drain holes or patch silicone sealant carries a risk of slipping and falling; wait for the rain to stop or call a tradesperson. If an exterior wall or window frame leaks in the rain, catch the water with towels and a bucket first, and do not run an extension cord to a dehumidifier near standing water. If seeping water reaches a socket, switch or wiring, turn off the appliances on that circuit and have a qualified plumbing and electrical worker check it; do not open up the socket yourself.
FAQ
Which months is the plum rain season?
May to June. The current page of the CWA climate portal compiles rainfall for the "plum rain season (May-June)"; the CWA's 2020 Q&A booklet says it was set starting in 1994. In climate terms the notable rain from the plum rain front mostly falls from mid-May to mid-June, but the timing differs from year to year.
Does typhoon season start as soon as the plum rain season ends?
There is a stretch in between. The CWA climate portal says that after mid-to-late June Taiwan's weather settles, with mainly afternoon thunderstorms, and the typhoon season does not start until mid-August. This is only the climate average and does not mean there will be no typhoon before mid-August.
Will this year's plum rain be heavy?
The outlook for the 2026 plum rain season was released on April 28 (Ministry of Transportation and Communications press release of April 28, 2026), predicting that this year's plum rain season is more likely to have normal to above-normal average temperatures and normal to below-normal rainfall. The outlook is a probability forecast and does not mean there will be no heavy rain.
Why does mold grow so easily in the plum rain season?
The CWA Q&A booklet explains that in the plum rain period the precipitation is mostly persistent and the air is humid, so things easily go moldy, which is why it is also called "mold rain." For removing and preventing mold on walls, see Getting rid of mold on home walls and preventing it.
Last updated: 2026-10-30
This article is compiled by SOSfix editors from public information and is for general reference only; for actual weather and warnings, rely on the latest releases from the Central Weather Administration, and for leaks and electrical problems, contact a qualified plumbing and electrical or waterproofing worker.
Sources
- Central Weather Bureau (中央氣象局), meteorology Q&A booklet (氣象常識問答集), March 2020 edition (in Chinese): Chapter 4, questions 5 and 6: causes of plum rain and its other name "mold rain," Taiwan's plum rain period of May to June, May to June set as the plum rain season from 1994 (this history appears only in this edition), plum rain season rainfall about 1/4 of the annual total, dry or missing plum rain; Chapter 4, question 1: share of losses from 1985 to 2017 (typhoons about 82%, plum rain 12.3%); the start and end of natural seasons remain to be researched.
- Central Weather Administration (CWA) climate portal: seasonal climate, plum rain season (viewed 2026-10-30) (in Chinese): the four stages (before mid-May, mid-May to mid-June, after mid-to-late June, mid-August typhoon season), the current "plum rain season (May-June)" wording, average rainfall of 440.7 mm at 11 lowland stations, 891.1 mm in 2012 and 193.4 mm in 1980, heavy-rain frequency in the west 2 to 4 times that of the east, the average 28th pentad for the summer monsoon onset with its normal range, and about 65% of years being close.
- Central Weather Administration (CWA) climate portal: climate encyclopedia, the plum rain season under climate change (viewed 2026-10-30) (in Chinese): large year-to-year variation in plum rain season rainfall, wettest and driest years (consistent with the item above).
- Ministry of Transportation and Communications press release: plum rain season temperatures normal to above normal, rainfall normal to below normal (April 28, 2026) (in Chinese): the 2026 plum rain season outlook, more concentrated rain and more frequent short bursts of intense rain, dredging drainage early, guarding against lightning strikes and strong gusts.
