Hong Kong's October Heat Records Reveal Warmer Days, Hotter Nights and Delayed Autumn Relief

October 2025 sets records for average and overnight warmth

Hong Kong recorded an average temperature of 27.4 degrees Celsius in October 2025, its highest October reading since records began in 1884, according to figures the Hong Kong Observatory announced on November 4. The average daily minimum reached 25.6 degrees, also an October record, as persistent high pressure over southern China delayed the arrival of cooler northern air.

The month included seven hot nights and four very hot days. On October 19, the temperature stayed at or above 28.2 degrees, making it the latest hot night recorded in any year. Rainfall totalled just 31.2 millimetres, about a quarter of the October normal.

The Observatory's dated October 2025 figures differ from another set attributed to the agency: an average temperature of 27.6 degrees, an average maximum of 30.5 degrees and an average minimum of 25.8 degrees, all described as records. The year attached to that higher set is unclear. For October 2025, the average maximum was 29.9 degrees, the second highest behind October 2024's 30.3 degrees.

Keeping the reporting periods separate matters for understanding the records. The dated 2025 announcement describes unprecedented average and overnight warmth, while the higher figures describe records across all three temperature measures.

What the three temperature measures tell us

The monthly average describes how warm October was across the month. The average maximum brings together each day's highest temperature, while the average minimum brings together each day's lowest. Together, they show whether unusual warmth was concentrated in daytime peaks or continued through the hours when people normally expect relief.

October 2025's record average minimum is especially relevant to residents trying to cool their homes at night. A month can become exceptionally warm even when its daytime average falls short of a previous record, if temperatures remain high after sunset.

The alternative figures also come with comparisons against the usual October conditions. The average maximum of 30.5 degrees was described as 2.4 degrees above normal, while the average of 27.6 degrees and average minimum of 25.8 degrees were each 1.9 degrees above normal. Those differences imply reference values of 28.1, 25.7 and 23.9 degrees respectively, although the reference period was not specified.

For October 2025, the average daytime maximum was 0.4 degrees below the October 2024 record, calculated from 29.9 and 30.3 degrees. Yet the monthly average and average minimum still reached new highs. The combination shows how much warm nights contributed to the month's persistent heat.

Why cooler air arrived late

The Observatory attributed October 2025's exceptional warmth to a stronger than normal upper air anticyclone over southern China. An anticyclone is an area of high atmospheric pressure. When it persists above a region, sinking air can limit cloud formation and favour sunshine, allowing the ground to heat up during the day.

The weather agency said cooler air from the north reached the southern China coast only later in the month. Hong Kong therefore spent more of October under conditions that supported heat before the seasonal change brought relief.

The explanation accompanying the higher temperature series named four influences: climate warming, an extremely strong El Niño event, a weaker than normal northeast monsoon and stronger than normal high pressure aloft. El Niño is a periodic warming of the central and eastern tropical Pacific that can alter weather patterns far beyond the ocean itself.

The northeast monsoon normally helps carry cooler continental air towards southern China. A weaker flow can leave Hong Kong warmer, while persistent high pressure supports sunny conditions. Climate warming raises the temperature baseline on which these changing weather patterns act.

Seven hot nights extended the heat into late October

Hong Kong experienced seven hot nights during October 2025, including four consecutive nights beginning on October 16. In the Observatory's terminology, a hot night has a daily minimum temperature of at least 28 degrees. A very hot day reaches a maximum of at least 33 degrees.

October 19 stood out because its minimum temperature was 28.2 degrees. Even at the coolest point of that day, the Observatory remained above the hot night threshold. Its timing established a record for how late in the calendar year such a night had occurred.

Warm nights affect daily life differently from a brief afternoon temperature peak. Homes have less opportunity to release accumulated heat, and residents may need cooling for longer. People without effective ventilation or air conditioning have fewer opportunities to escape the warmth.

The month's four very hot days added daytime exposure to those uncomfortable nights. The figures describe a prolonged warm spell across different parts of the daily cycle, rather than simply one unusually hot afternoon.

From a hot National Day to a sharp temperature drop

October 2025 began with sunshine and very hot conditions under high pressure aloft. The Observatory's temperature reached 33.6 degrees on October 1, the month's highest reading. Another spell of generally fine and very hot weather followed from October 7 to 11, interrupted by a few showers.

The Hong Kong Observatory, the city's official weather agency, described the opening conditions in its monthly account:

Under the influence of an anticyclone aloft, the local weather was generally fine and very hot on the first three days of the month.

October 8 reached 33.1 degrees at the Observatory, making it the hottest Cold Dew on record. Cold Dew is one of the 24 solar terms in the traditional Chinese calendar, associated with the transition towards cooler weather. In 2025, the weather remained hot despite that seasonal marker.

The main temperature changes during the dated October 2025 account were:

• October 1: The Observatory reached 33.6 degrees, the month's maximum.
• October 8: A maximum of 33.1 degrees set a record for Cold Dew.
• October 16 to 19: Four consecutive hot nights occurred.
• October 19: A minimum of 28.2 degrees marked the latest hot night of any year.
• October 22: The temperature fell to 18.2 degrees, the month's minimum.
• November 4: The Observatory announced the October records.

The change from October 19 to October 22 was abrupt: the daily minimum fell by 10 degrees, from 28.2 to 18.2 degrees. Severe Tropical Storm Fengshen and an intense northeast monsoon combined to bring the cooler conditions.

A dry month despite tropical cyclone activity

October 2025's rainfall of 31.2 millimetres was well below the normal 120.3 millimetres. The shortfall was 89.1 millimetres, meaning the month received about 26 percent of normal rainfall, or roughly three quarters less than usual.

Tropical cyclones still brought episodes of unsettled weather. Typhoon Matmo brought strong winds, squally showers and violent gusts during the first week. Later, Fengshen and the northeast monsoon helped end the heat with a sharp temperature drop.

Rainfall totals measure how much water accumulated across the month, while cyclone conditions can change rapidly over a shorter period. Hong Kong experienced disruptive wind and showers within a month that remained unusually dry.

The Observatory said in early October that Hong Kong had already experienced at least 12 tropical cyclone warning episodes during 2025, a record since 1946. That placed the October heat within a year of unusually frequent cyclone warnings.

Cooler forecasts depend on location as well as wind

The outlook accompanying the higher temperature series anticipated a fresh to strong northeast monsoon reaching the Guangdong coast, followed by an additional supply of dry air. Breezy conditions and a few light showers were expected before temperatures eased early the following week.

Urban temperatures were forecast to range from 23 to 27 degrees on Monday, with a minimum of 22 degrees on Tuesday. Some locations, including Tseung Kwan O, Ta Kwu Ling and Shek Kong, were forecast to approach 19 degrees. Those are the expectations issued with that account, rather than a current forecast.

The same outlook predicted easterly winds of force 4 to 5, occasionally reaching force 6 offshore and force 7 on high ground. Wind force describes wind strength, with larger numbers indicating stronger winds.

Local observations also showed why a single city temperature cannot describe every neighbourhood. During the warm conditions accompanying that outlook, the urban maximum was 29.5 degrees, while Lau Fau Shan reached 33.6 degrees, Yuen Long Park 33.5 degrees and Sheung Shui 33 degrees.

Key Points

• October 2025 averaged 27.4 degrees Celsius, with an average minimum of 25.6 degrees, both October records.
• The average maximum was 29.9 degrees, second to October 2024's 30.3 degrees.
• Seven hot nights occurred, including the latest ever recorded, on October 19.
• Rainfall totalled 31.2 millimetres, about 26 percent of the October normal.
• Persistent high pressure delayed cooler air, before Fengshen and the northeast monsoon brought a sharp temperature drop.
• A higher temperature series of 27.6, 30.5 and 25.8 degrees has an unclear reporting year and should be kept separate from the dated 2025 figures.