Hong Kong Enters Rainy Season in April, Annual Rainfall Expected to Be Near Normal
As April approaches, Hong Kong is about to officially enter its annual rainy season. The Hong Kong Observatory (HKO) stated that the city’s rainy season generally runs from April to September, during which about 80 percent of the annual rainfall is concentrated. In its annual outlook released on March 23, the Observatory indicated that the total annual rainfall in Hong Kong for 2026 is expected to be near normal, ranging between 2,100 and 2,700 millimeters.
Climate Characteristics of the Rainy Season: April Humid and Foggy, May to August Hot with Frequent Showers
According to HKO data, Hong Kong is located in the subtropics. March and April are relatively warm but at times extremely humid. Fog and drizzle can reduce visibility, sometimes affecting air and ferry services. From May to August, the weather is hot and humid with occasional showers and thunderstorms, which are more common in the morning. Afternoon temperatures often exceed 31 degrees Celsius.
In terms of rainfall distribution, the average annual rainfall varies significantly across different districts of Hong Kong. For example, Peng Chau receives about 1,400 millimeters, while areas near Tai Mo Shan receive over 3,000 millimeters. June and August are typically the wettest months, while January and December are the driest.
Thunderstorms and Tropical Cyclones: High-Risk Period from May to September
The HKO noted that severe weather affecting Hong Kong includes tropical cyclones, intense monsoons, monsoon troughs, and frequent thunderstorms from April to September. Data shows that thunderstorms are common in Hong Kong from April to September, and the annual number of thunderstorm days recorded at HKO headquarters showed an increasing trend of about 1.6 days per decade between 1947 and 2012.
Additionally, Hong Kong may be affected by tropical cyclones of varying intensities from May to November, with July to September being the months most likely to be affected by such cyclones. The Observatory predicts that the number of tropical cyclones entering within 500 kilometers of Hong Kong in 2026 will be near normal, approximately 4 to 7, and the typhoon season may begin in June or later and end in October or earlier.
Extreme Rainfall Trends: Increasing Frequency of Short-Duration Intense Rainfall
It is worth noting that extreme rainfall events in Hong Kong have shown an increasing trend in recent years. HKO analysis indicates that between 1947 and 2012, the number of “heavy rain days” – when hourly rainfall exceeds 30 millimeters – increased at a rate of 0.2 days per decade. Over the past century or more, the frequency of record-breaking hourly rainfall at HKO headquarters has shifted from once every few decades to repeatedly breaking records in recent decades.
For example, in August 2025, Hong Kong experienced a black rainstorm warning that lasted more than 11 hours, becoming the second-longest black rain event on record. The HKO headquarters recorded 355.7 millimeters of rainfall, breaking the highest single-day rainfall record for August since 1884. The heavy rain caused severe flooding in many districts. A car park in Tseung Kwan O was submerged twice, and traffic on Tai Po’s Bride’s Pool Road was disrupted due to the collapse of a roadbed.
Rainstorm Warning System: Three-Tier Alert Mechanism
The Hong Kong Observatory operates a three-tier rainstorm warning system to alert the public to approaching heavy rain. The Amber Rainstorm Warning Signal indicates that heavy rain exceeding 30 millimeters per hour has been recorded or is expected across a wide area of Hong Kong and may persist. The Red Rainstorm Warning Signal indicates that rainfall has reached more than 50 millimeters per hour, while the Black Rainstorm Warning Signal indicates that rainfall has reached more than 70 millimeters per hour.
The HKO noted that when the Red or Black Rainstorm Warning Signal is issued, students who have already left home should continue on their way to school, and schools must keep their premises open until normal dismissal time. Employers should not require employees to report for work during a Black Rainstorm warning unless prior arrangements have been made.
Additionally, the HKO also issues Localized Heavy Rain Advisories. When heavy rain exceeding 70 millimeters per hour is recorded or expected in a particular area but does not meet the threshold for issuing a Red or Black Rainstorm Warning on a wide scale, the Observatory will issue a relevant advisory to remind residents in the affected area to take preventive measures.
Recommendations: Public Should Prepare Early
As the rainy season approaches, the HKO urges the public to take the following precautions:
- Check the latest weather warnings and radar images issued by the Observatory before going out
- Carry rain gear at all times, and avoid visiting mountain streams, rivers, and low-lying areas during heavy rain
- Residents in low-lying areas should check drainage systems in advance; fishpond operators may consider lowering pond water levels to reduce potential losses
- If a Black Rainstorm Warning is issued, stay in a safe place and take shelter until the heavy rain has passed.
The Hong Kong Observatory stated that it will closely monitor weather changes and issue timely warnings. The public can obtain the latest weather information through the Observatory’s website, the “MyObservatory” mobile app, and the media.