Will Hong Kong have between 70-120mm of precipitation in October?

- [2026-10-07] Hong Kong Observatory said this year's typhoon season is expected to end by October, with sea surface temperatures in the South China Sea having dropped and an anticyclonic circulation anomaly suppressing deep convection "since late September," conditions expected to persist "through late October, making tropical cyclones unlikely to form." https://clb.org.hk/en/hong-kong/Hong-Kong-typhoon-season-likely-over-as-October-cyclone-risk-c51907 - [2026-10-08] The Standard reported only three tropical cyclones have required warning signals in Hong Kong so far this year, and "low sea temperatures and localized atmospheric circulation" make direct typhoon hits unlikely for the rest of October, though three Pacific systems (Choi-wan, Koguma, Nolo) are tracking toward Japan rather than Hong Kong. https://www.thestandard.com.hk/news/article/344936/Hong-Kong-unlikely-to-face-direct-typhoon-hit-for-rest-of-October-HKO-says - [2026-10-07] As of Oct 6, 2026, a total of 34 tropical cyclones had affected the western North Pacific/South China Sea region year-to-date (well above the long-term average of ~21 for Jan–Sep), but only three entered within 500 km of Hong Kong, "fewer than the long-term average of about five," meaning weak direct typhoon-driven rain influence on HK in 2026 overall. https://english.dotdotnews.com/a/202610/07/AP6ac5e897e4b02724bdb6a38c.html - [2026-09-30] HKO's official Monthly Forecast for October 2026 (assessment dated 30 Sep 2026) states Hong Kong is expecting "normal to above-normal temperature" and "normal to below-normal rainfall," with the monsoon trough/anticyclone aloft expected to weaken slightly only in the latter part of the month, "favouring more rainfall over the region" later on. https://www.hko.gov.hk/en/wxinfo/month/month.htm - [2026-10-10] HKO's current 9-day outlook (published on its homepage, viewed 2026-10-10) forecasts "mainly fine," "dry" conditions from Oct 10 through Oct 14 with a "Low" Probability of Significant Rain each day, turning to "sunny periods" with "one or two light rain patches" on Oct 15–16, still rated "Low" probability of significant rain through Oct 18. https://www.weather.gov.hk/contente.htm - [2026-07-31] HKO's Annual Outlook assessment (as of 31 July 2026) noted that cumulative rainfall for the year-to-date was 1906.7 mm, "30.9% above" the normal value for the period, reflecting an unusually wet summer ahead of a drier autumn forecast. https://www.hko.gov.hk/en/wxinfo/season/anlf.htm - [2026-08-31] HKO's Seasonal Forecast for September–November 2026 (assessment as of 31 Aug 2026) expected "normal to above-normal temperature" and "normal to below-normal rainfall," with the chance of below-normal rainfall "slightly higher" for the SON period. https://www.hko.gov.hk/en/wxinfo/season/season.htm - [2026-10-10] Third-party seasonal-forecast aggregator WeatherTab's October 2026 outlook characterizes early October (Oct 1–10) as having relatively higher rain risk ("fewest DryDays"), with mid-October (Oct 11–20) moderate, and late October (Oct 21–31) having lower rain risk ("more DryDays"), consistent with a front-loaded, otherwise drying month. https://www.weathertab.com/en/c/10/hong-kong-special-administrative-region/hong-kong/ - [2026-10-10] HKO's climatological "Daily Extract" tool for October 2026 (the question's designated resolution source) is a dynamic, JavaScript-driven lookup page; no cumulative October-to-date rainfall figure could be retrieved directly from the static fetch, meaning the live running total for Oct 1–9, 2026 was not independently confirmed from primary data in this research pass. https://www.weather.gov.hk/en/cis/dailyExtract.htm?y=2026&m=10 NOT FOUND: The exact cumulative Hong Kong Observatory headquarters rainfall total (mm) actually recorded from October 1–9, 2026 (the Daily Extract table did not render in text form); any specific rain event or rainstorm warning signal issuance inside Hong Kong during October 1–10, 2026 (none was reported in searched sources, consistent with the "mainly fine/dry" forecast); and the October climatological normal figure (1991–2020 baseline) for HKO headquarters, which several third-party sites estimate at roughly 75–150 mm but which was not confirmed on HKO's own normals page. BOTTOM LINE: As of 2026-10-10, Hong Kong's typhoon season is officially winding down with low cyclone risk for the rest of October and HKO's own 9-day forecast shows mostly dry, low-rain-probability conditions through at least Oct 18, while HKO's October monthly outlook itself favors "normal to below-normal" rainfall; this near-term dry pattern, if it persists into the second half of the month, points toward the lower end of (or below) the 70–120mm bracket, though HKO's official normal/below-normal tilt for October 2026 and typical October climatology (often cited in the 75–150mm range by secondary sources) keep the 70-120mm band plausible if even one moderate rain event occurs later in the month.

- [2021-01] The 1991-2020 climatological normal for October rainfall in Hong Kong is 120.3 mm, with 50 hours of rainfall duration, 7.83 days with 0.1mm or more, 1.33 days with 25mm or more, and 0.77 days with 50mm or more , source: HKO Climatological Normals. https://www.hko.gov.hk/en/cis/normal/1991_2020/normals.htm - [2026-09-30] HKO's official Monthly Forecast for October 2026 (issued as of 30 Sept 2026) states Hong Kong is expecting normal to above-normal temperature and normal to below-normal rainfall, with an anti-cyclone aloft covering the coast of southern China and northern South China Sea for most of October, and a relatively weak northeast monsoon , and overall rainfall over the coast of southern China in October is expected to be normal to below-normal, though the anti-cyclone aloft will weaken slightly in the latter part of the month, favouring more rainfall . https://www.hko.gov.hk/en/wxinfo/month/month.htm - [2026-09-30] HKO's assessment explicitly says "the chance of normal to below-normal rainfall in the month will be higher" for October 2026, implying the official forecast leans toward a below-120mm outcome rather than the 70-120mm bracket being favored. https://www.hko.gov.hk/en/wxinfo/month/month.htm - [2025-11-03] October 2025 actual rainfall was 31.2 millimetres, only about 26 percent of the normal of 120.3 millimetres — below the 70-120mm bracket. https://www.hko.gov.hk/en/wxinfo/pastwx/mws2025/mws202510.htm - [2024-11] October 2024 actual rainfall was 11.3 millimetres, only about 9 percent of the normal figure of 120.3 millimetres — far below the bracket. https://www.ncei.noaa.gov/monitoring-content/sotc/global/2024/oct/HongKong-MonthlyReport-202410.pdf - [2023-11] October 2023 rainfall was 546.0 millimetres, more than four times of the normal figure of 120.3 millimetres and the fifth highest on record for October , driven by Typhoon Koinu — far above the bracket. https://www.hko.gov.hk/en/wxinfo/pastwx/mws2023/mws202310.htm - [2022-11] October 2022 rainfall was only 49.9 millimetres, about 41 percent of the normal of 120.3 millimetres — below the bracket. https://www.hko.gov.hk/en/wxinfo/pastwx/mws2022/mws202210.htm - [2021-11-02] October 2021 rainfall amounted to 631.1 millimetres, more than five times of the normal figure of 120.3 millimetres... the second highest on record for October , due to tropical cyclones Lionrock and Kompasu — far above the bracket. https://www.weather.gov.hk/en/wxinfo/pastwx/mws2021/mws202110.htm - [2020-11-03] October 2020 rainfall was 142.4 millimeters, about 41 percent above the normal of 100.9 millimetres (old normal) — above the bracket. https://www.hko.gov.hk/en/wxinfo/pastwx/mws2020/mws202010.htm - [2019-11] October 2019 rainfall was 149.5 millimetres, about 48 percent above the normal of 100.9 millimetres — above the bracket. https://www.hko.gov.hk/en/wxinfo/pastwx/mws2019/mws201910.htm - [2026-10-08] HKO's local news report indicated Hong Kong was facing active typhoon development in the western North Pacific with systems Choi-wan, Koguma, and Nolo expected to track northwards toward Japan rather than directly threatening Hong Kong in early-to-mid October 2026, and a related headline noted Hong Kong was unlikely to face a direct typhoon hit for the rest of October. https://www.thestandard.com.hk/news/article/344936/Hong-Kong-unlikely-to-face-direct-typhoon-hit-for-rest-of-October-HKO-says BOTTOM LINE: Looking at the last 7 Octobers (2019-2025), Hong Kong's October rainfall has been strongly bimodal — either well below 70mm (2022, 2024, 2025) or well above 120mm (2019, 2020, 2021, 2023), driven by whether a tropical cyclone directly affects the city that month; in none of these 7 years did the total fall inside the 70-120mm band, suggesting a historically low base rate for this specific bracket despite it containing the long-term mean (120.3mm). HKO's own October 2026 outlook leans toward "normal to below-normal" rainfall with no imminent direct typhoon threat reported as of early October, which (combined with the historical bimodality) tilts the outside view toward a "No" (dry, sub-70mm) outcome more than a mid-range 70-120mm result, though a late-month typhoon remains a wildcard that has pushed many past Octobers well above the bracket instead. NOT FOUND: A complete year-by-year (e.g., 20-30 year) dataset or official frequency/probability distribution from HKO showing how many historical Octobers specifically fell within the 70-120mm range; no Polymarket- or bookmaker-specific odds history for this contract (per instructions, not sought/reported).

YES means: Hong Kong Observatory's finalized "Total Rainfall (mm)" for October 1–31, 2026 (HKO Daily Extract) falls in the 70.0–120.0mm band (with exact ties rounding to the higher bracket). - [2026-10-02] A trough-related shower/thunderstorm system triggered a Yellow Rainstorm Warning at 17:40 HKT, with HKO reporting Sheung Shui/North District had "已錄得超過70毫米雨量" (over 70mm in one hour) and Tai Po also flagged for similarly intense rain, prompting a Northern New Territories Flooding Special Announcement. https://news.tvb.com/tc/1198611-天氣天文台下午5時40分發出黃雨警告大埔區雨勢特別大 - [2026-10-03] A second Yellow Rainstorm Warning was issued at 04:00 HKT and a Thunderstorm Warning was extended to 09:00, confirming the early-October rain event spanned at least two calendar days, not a single brief shower. https://news.rthk.hk/rthk/ch/component/k2/1872499-20261003.htm - [2026-10-04] A third Yellow Rainstorm Warning was issued at 17:40/20:20 HKT, with Tai Mei Tuk recording 52mm in one hour (red-rain-level intensity) and Wong Tai Sin, Sha Tin and Kowloon City all exceeding 30mm/hour, showing the rain event recurred on a third day. https://github.com/qjlxg/wei/issues/3011 - [2026-10-04] HKO's own 9-day forecast text (issued 21:45 HKT) described a cold front "逐漸橫過廣東沿岸" bringing showers and squally thunderstorms that night with locally heavy rain before clearing mid-week, confirming a genuine multi-day rain episode, not just isolated warnings. https://www.hkww.org/weather/chinese/weather5.php - [2026-10-01] HKO's own 9-day forecast issued 11:30 HKT on Oct 1 explicitly called for "有幾陣驟雨及雷暴，部分地區雨勢較大" (showers and thunderstorms, locally heavy) for Oct 2 and continuing scattered showers through Oct 5, meaning HKO itself anticipated a wet opening week before the dry/sunny pattern set in later. https://www.hko.gov.hk/textonly/v2/forecast/ndayc.htm - [2026-10-07] HKO's own commentary piece conceded that while a direct typhoon hit is unlikely for the rest of October, it explicitly limited the "unlikely" assessment to direct tropical-cyclone impacts, not to all rain sources (monsoon troughs, cold fronts, upper-air disturbances), leaving room for non-cyclonic rain to still accumulate meaningfully. https://www.singtaousa.com/2026/10/07/news/china/tropical-cyclone-outlook-october-hong-kong/ - [2026-09-30] HKO's monthly forecast, despite leaning "normal to below-normal," explicitly notes the anti-cyclone aloft "will weaken slightly in the latter part of the month, favouring more rainfall over the region," meaning HKO's own official outlook contains a built-in bullish-rain scenario for late October that could push an otherwise dry month up into the 70-120mm band. https://www.hko.gov.hk/en/wxinfo/month/month.htm - [2026-10-10] WeatherTab's aggregator (cited by colleagues) itself concedes early October (Oct 1–10) carries the "fewest DryDays" of the month, i.e., the highest rain-risk window, which aligns with the confirmed Oct 2–4 rainstorm sequence and suggests the month did not open as dry as the subsequent Oct 10–18 forecast implies. https://www.weathertab.com/en/c/10/hong-kong-special-administrative-region/hong-kong/ BOTTOM LINE: Contrary to the impression of a uniformly dry October, HKO itself issued three separate Yellow Rainstorm Warnings (Oct 2, 3, and 4) with hourly rates locally exceeding 70mm and even reaching red-rain intensity (52mm/hr) at Tai Mei Tuk — a genuine multi-day, moderate-to-heavy rain event in the first week that could plausibly have deposited several tens of mm basin-wide at HKO HQ; if this front-loaded rainfall (easily capable of contributing 20-50+mm) is followed by even one further moderate shower episode in late October (which HKO's own forecast flags as more likely once the blocking anticyclone weakens), the month could land inside the 70-120mm bracket rather than the sub-70mm outcome the "mostly dry" headline forecasts might suggest. NOT FOUND: The precise confirmed cumulative rainfall total (mm) recorded at HKO Headquarters for the Oct 2–4, 2026 rainstorm episode specifically (only hourly/localized district figures were available in searched sources, not the HKO-HQ daily or multi-day sum); the exact Oct 1–9 running total from the Daily Extract tool, which remained inaccessible as a static fetch.

YES means: Hong Kong Observatory's "Daily Extract" total precipitation for Oct 1–31, 2026 at HKO headquarters is recorded, after rounding-to-higher-bracket rule, as between 70.0mm and 120.0mm inclusive. The NO case argues the final figure lands outside that band (most plausibly below 70mm, given the forecast and historical pattern, though a late typhoon could push it above 120mm instead). - [2026-10-07] The three tropical cyclones that actually triggered Hong Kong warning signals in 2026 to date were identified by name for the first time as "Only three tropical cyclones have required warning signals in Hong Kong so far this year" , specifically Maysak, Noul and Saudel, with Noul skirting the city "at a distance of about 80 km northeast on 26 July, leading the weather watchdog to issue the Increasing Gale or Storm Signal No. 9" , none of which occurred in October, meaning none of this year's rain-heavy tropical systems contributed to the October tally. https://clb.org.hk/en/hong-kong/Hong-Kong-typhoon-season-likely-over-as-October-cyclone-risk-c51907 - [2026-10-07] HKO's own count shows regional cyclone activity was unusually high (34 systems) but direct Hong Kong impact unusually low: "34 tropical cyclones have formed across the western North Pacific and South China Sea as of October 6 — significantly higher than the long-term January-September average of 21. Twelve of these systems formed in August alone, setting a record for the highest single-month total since 1961." This confirms the rain-bearing storm track has largely bypassed Hong Kong, reducing the odds of an October cyclone rain event that would be needed to reach even the 70mm floor. https://www.thestandard.com.hk/news/article/344936/Hong-Kong-unlikely-to-face-direct-typhoon-hit-for-rest-of-October-HKO-says - [2026-10-04/05] The only confirmed rainstorm-warning event so far in October 2026 was brief and localized: an amber rainstorm signal was issued at 8:20pm on Oct 4 and cancelled by 10:30pm the same night, roughly two hours in total duration, triggered by "a few squally thunderstorms" and a cold front moving across Guangdong, not a prolonged or territory-wide soaking event. https://www.scmp.com/news/hong-kong/health-environment/article/3369718/hong-kong-issues-amber-rainstorm-warning - [2026-10-07] HKO's explicit reasoning for low October rain risk cites a specific physical mechanism beyond generic "below-normal" wording: "Sea surface temperatures in the South China Sea have dropped, and the anticyclonic circulation anomaly has been suppressing the development of deep convective clouds over the South China Sea and the Philippines region since late September... The latest climate models generally indicate these unfavourable conditions will persist through late October, making tropical cyclones unlikely to form." A persistent anticyclone aloft (subsidence) suppresses not just typhoons but general convective/monsoon rainfall, which is the dominant non-cyclone rain source in October. https://clb.org.hk/en/hong-kong/Hong-Kong-typhoon-season-likely-over-as-October-cyclone-risk-c51907 - [2026-10-10] HKO's 9-day outlook as of this date shows essentially zero rain risk through Oct 12, forecasting "Fine. Dry during the day" with "Low" probability of significant rain on both Oct 11 and Oct 12, meaning roughly one-third of the month (with no rain so far after the Oct 4 squall) risks ending with negligible contribution to the monthly total if this pattern holds. https://www.weather.gov.hk/contente.htm - [2026 (historical)] The precedent years that most resemble 2026's "no direct typhoon, below-normal forecast" setup — 2022, 2024 and 2025 — did not merely fall short of 120mm; they landed at 49.9mm, 11.3mm and 31.2mm respectively, each far under the 70mm floor rather than inside the 70–120mm band, indicating that when HKO's forecast and typhoon-season narrative mirror this year's, the realized outcome has historically undershot the band entirely rather than landing inside it. (Figures as cited in colleagues' base-rate section, sourced to HKO monthly weather summaries.) - [2026-10-04] The cold-front/monsoon-trough rain event on Oct 4 was itself only a 70 km/h gust, squally-thunderstorm event rather than a sustained heavy-rain system, and HKO's own amber-signal definition requires "heavy rain exceeding 30mm in an hour" generally over the territory — a threshold met only briefly, suggesting the event's net contribution to the monthly total was likely modest (tens, not scores, of mm) rather than enough alone to secure the 70mm floor. https://www.scmp.com/news/hong-kong/health-environment/article/3369718/hong-kong-issues-amber-rainstorm-warning - [2026-10-07] HKO's statement that the "chance of normal to below-normal rainfall in the month will be higher" was reaffirmed in the Oct 7 typhoon-season briefing without any walk-back or upward revision as the month began, i.e., the official forecast has not moved toward the 70–120mm band even after a week of October data became available. https://www.thestandard.com.hk/news/article/344865/Typhoon-season-winds-down-as-HK-faces-low-October-risk BOTTOM LINE: With Hong Kong's local typhoon season officially declared over for practical purposes, the anticyclonic subsidence pattern explicitly forecast to persist through late October, and the only confirmed October rain event so far (the Oct 4 amber warning) having been brief and localized, the mechanism and recent-years precedent both point toward a sub-70mm outcome rather than the 70–120mm band, supporting a NO resolution unless an unexpected late-month rain event (non-cyclonic trough or unseasonal disturbance) materializes. NOT FOUND: The actual cumulative HKO headquarters rainfall figure for October 1–9/10, 2026 (the Daily Extract tool did not render a text-retrievable total); any specific millimeter total attributed to the Oct 4 amber-warning event at HKO headquarters; confirmation of whether any additional rainstorm signals were issued between Oct 5 and Oct 10, 2026.