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TC Watch / 熱帶氣旋 > Selected TC Review / 重要熱帶氣旋回顧 > 202517W [Refresh 更新]

202517W - Profile 檔案

(First draft issued on August 20, 2025, final version issued on April 18, 2026)
(初稿於 2025 年 8 月 20 日發出，最後版本於 2026 年 4 月 18 日上載)

Brief profile of 17W | 17W 小檔案:

^Refers to the period between the HK Observatory's first and last bulletins for the tropical cyclone (with at least tropical depression intensity). For storms formed/dissipated/transformed into an extratropical cyclone outside the area bounded by 7-36°N and 100-140°E, information from the JTWC will be used instead.
^即香港天文台為該熱帶氣旋（熱帶低氣壓級或更高）作出發佈的時期。至於在北緯 7 至 36 度、東經 100 至 140 度外形成／消散／轉化為溫帶氣旋的風暴，本網將參考聯合颱風警報中心的資料。

TC signals in Hong Kong* 香港曾經生效的熱帶氣旋警告*:

Signal 信號	Date and time 日期和時間	Distance from HK 與香港的距離	Predicted movement 預測移動趨勢	Max. 10-min winds 中心最高十分鐘平均風速
	2025/08/16 (SAT) 22:20 HKT	SSW 690 km	NW at 18 km/h	45 km/h (25 knots, TD)
	2025/08/17 (SUN) 20:20 HKT**	SW 680 km	WNW at 15 km/h	45 km/h (25 knots, TD)

*Based on the information from real-time tropical cyclone warning bulletins.
*根據實時熱帶氣旋警報資料。

**The Strong Monsoon Signal was issued at 20:21 HKT.
**強烈季候風信號於下午 8 時 21 分發出。

Percentile Ranks 百分等級:

IR imagery animation 紅外線雲圖動畫:

TC track from HKWW 本站的熱帶氣旋路徑圖:

TC track(s) from HKO 天文台的熱帶氣旋路徑圖:

Past HKWW Bulletins 本站發佈

Please click here for bulletins on this tropical cyclone. 請按這裡。

Storm Development Overview 風暴發展概覽

Unless otherwise stated, all times below are in Hong Kong Standard Time (UTC+8)
除非特別註明，下文時間均為香港標準時間（協調世界時加 8 小時）

A large monsoon depression formed in the South China Sea in mid-August. The system, designated as tropical disturbance 91W, had a very loose core but vigorous peripheral convective activities. Numerical models generally predicted that 91W would move towards Hainan Island and the Gulf of Tonkin in response to the subtropical ridge to the northeast.

The NMC upgraded 91W into a tropical depression at 5 pm August 16. Its initial forecast pointed 91W towards eastern Hainan. Meanwhile, the HKO upgraded the system at 9:30 pm. As 91W would make landfall soon and due to its monsoon depression nature, development was expected to be slow and the system was not expected to intensify to beyond tropical depression strength.

Later on August 17, 91W's core structure tightened. As the system developed, it moved in a more westerly direction than previously forecast. Instead of making landfall at Hainan, 91W skirted the seas southwest of the island in the small hours of August 18. Convective bursts were seen developing near its centre, and the JTWC issued a tropical cyclone formation alert at 8 am. It upgraded 91W into tropical depression 17W six hours later.

17W's convections strengthened while it travelled north in the Gulf of Tonkin. Nevertheless, 17W remained as a tropical depression throughout. According to the NMC, 17W made landfall in northeastern Vietnam near 4:15 am August 19, with winds of around 14 m/s (50 km/h). 17W continued to move north into Guangxi province, and weakened into an area of low pressure that night.

一個大型季風低壓於 8 月中在南海形成。該系統的擾動編號為 91W，其中心非常鬆散，但外圍對流活動旺盛。數值模式普遍預料，受東北方副熱帶高壓脊的影響， 91W 將移向海南島及北部灣一帶。

中國中央氣象台於 8 月 16 日下午 5 時將 91W 升格為熱帶低氣壓，其初始預報顯示 91W 會移向海南東部。香港天文台則於下午 9 時 30 分將該系統升格。由於 91W 將於不久後登陸，加上它屬於季風低壓，因此預料其發展會較為緩慢，並且不會增強至熱帶低氣壓以上強度。

8 月 17 日稍後，91W 的中心結構變得緊密。隨著系統發展，它移動方向較先前預測偏西。91W 並未登陸海南，而是於 18 日凌晨掠過該島西南方海域。系統近中心有較明顯的對流爆發，聯合颱風警報中心於上午 8 時發出熱帶氣旋形成警報，繼而於 6 小時後將其升格為熱帶低氣壓 17W。

17W 向北移動並橫過北部灣，期間其對流有所增強，但始終維持熱帶低氣壓強度。中央氣象台表示 17W 於 19 日上午 4 時 15 分左右登陸越南東北部，近中心風速達每秒 14 米（每小時 50 公里）。17W 其後繼續北移並進入廣西省，當晚減弱為低壓區。

Weather in Hong Kong During Approach 風暴影響時香港天氣狀況

Link to relevant HKO weather report bulletins: 16/8 ● 17/8
香港天文台相關天氣報告連結： 16/8 ● 17/8

In Hong Kong, it was mainly sunny on August 16 under the influence of the subtropical ridge in southeastern China. At noon August 16, the Observatory indicated that the area of low pressure in the South China Sea might develop into a tropical cyclone, and that tropical cyclone warning signals would be considered around midnight the earliest.

Following the upgrade of 17W into a tropical depression at 9:30 pm, the Observatory said the #1 Standby Signal would be issued at 10:20 pm, and that local winds would strengthen on August 17 due to the combined influence of the tropical depression and the ridge in southeastern China. 17W was situated about 690 km south-southwest of Hong Kong when the #1 Signal was issued.

The local weather turned unstable in the morning of August 17. Squally showers started to affect the territory, and some places saw an increase in wind speeds. Sustained gale force winds were observed at Ngong Ping, while strong force winds were observed at a number of stations. In particular, the winds at Central Pier within the Victoria Harbour briefly reached strong force just after noon.

As 17W moved more westwards than predicted, it was closest to Hong Kong that morning as well. The Observatory initially suggested that it would assess the need to issue the #3 Strong Wind Signal, but changed its stance at 5 pm to suggesting that the Strong Monsoon Signal might be considered that night instead. The #1 Standby Signal was eventually cancelled at 8:20 pm, when 17W was about 680 km southwest of Hong Kong. The Strong Monsoon Signal was issued one minute later, with the warning that gusts might reach gale force. It is worth noting that, in Macau, the #3 Signal was in force between noon and 11 pm August 17.

An intense rainband approached the territory from the south near midnight August 18. The Amber Rainstorm Warning was issued at 12:30 am, and it was upgraded to Red at 1:15 am. The rain was especially heavy in the outlying islands and Tsuen Wan District, where an hourly rainfall in excess of 70 mm was recorded. At 5:30 am, the Education Bureau announced that the classes of all morning and whole-day schools would be suspended that day. The Rainstorm Warning was downgraded to Amber at 6:05 am as the rain became less intense, and it was cancelled at 7:20 am.

The weather remained unstable with occasional heavy showers on August 18. Most places in Hong Kong recorded more than 70 mm of rain that day, with the Observatory recording 80.1 mm. The active southerly airstream to the east of 17W continued to affect Hong Kong on August 19.

香港方面，受中國東南部副熱帶高壓脊的影響，8 月 16 日大致天晴。16 日正午，天文台表示位於南海的低壓區有機會發展為熱帶氣旋，最早於當晚午夜前後評估是否需要發出熱帶氣旋警告信號。

於下午 9 時 30 分升格 17W 為熱帶低氣壓後，天文台表示將於下午 10 時 20 分發出一號戒備信號，而受 17W 及中國東南部高壓脊的共同影響，8 月 17 日本港風勢將會增強。一號信號發出當時，17W 位於香港西南偏南約 690 公里。

香港天氣於 8 月 17 日早上轉趨不穩定，狂風驟雨開始影響本港，部分地區風速有所上升。昂坪錄得持續烈風風力，而一部份風速站錄得強風；位於維港內的中環碼頭亦於中午過後短暫吹強風。

由於 17W 移向較預期偏西，它於當日上午已經最接近本港。天文台初時表示將評估是否需要改發三號強風信號，但於下午 5 時指出會於當晚考慮以強烈季候風信號取代一號信號。一號信號最終於下午 8 時 20 分取消，17W 當時位於香港西南約 680 公里。強烈季候風信號則於一分鐘後發出，天文台表示陣風或達烈風程度。值得留意的是澳門曾發出三號風球，於 17 日正午至下午 11 時期間生效。

一道較強雨帶於 8 月 18 日近午夜從香港以南靠近。黃色暴雨警告於上午 12 時 30 分發出，並於上午 1 時 15 分升級為紅色。離島及荃灣雨勢特別大，一小時雨量曾達 70 毫米。上午 5 時 30 分，教育局宣佈所有上午校及全日制學校當天停課。隨著雨勢減弱，暴雨警告於上午 6 時 05 分轉為黃色，而該警告亦於上午 7 時 20 分取消。

8 月 18 日餘下時間天氣仍然不穩定，間中有大驟雨，多區全日雨量達 70 毫米，天文台則錄得 80.1 毫米。於 17W 東面的活躍偏南氣流於 19 日繼續影響本港。

Image Gallery 圖片庫

Figure 1 - ECMWF ensemble forecast at 8 am August 14
圖 1 - 8 月 14 日上午 8 時之 ECMWF 模式集成預報

Figure 2 - Satellite image of the monsoon depression before 17W's formation
圖 2 - 17W 形成前季風低壓之衛星雲圖

Figure 3 - Initial forecast tracks from NMC (left) and HKO (right)
圖 3 - 中央氣象台（左）及香港天文台（右）之初始預測路徑圖

Figure 4 - Steering flow chart at 8 am August 17
圖 4 - 8 月 17 日上午 8 時之駛流場分佈圖

Figure 5 - Wind field analysis map at 9:25 am August 17
圖 5 - 8 月 17 日上午 9 時 25 分之風場分析圖

Figure 6 - Radar image at 1 am August 18
圖 6 - 8 月 18 日上午 1 時之雷達圖

Figure 7 - Satellite image of 17W at 9 pm August 18
圖 7 - 8 月 18 日下午 9 時 17W 之衛星雲圖

Figure 8 - Daily rainfall distribution map for August 17 (left) and 18 (right)
圖 8 - 8 月 17 日（左）及 18 日（右）之雨量分佈圖

Winds Recorded at Reference Stations 參考站所錄得的風速

The following table lists the maximum 10-minute average (sustained) wind speed recorded while tropical cyclone signals were in force. In some occasions, it is possible that the strongest winds were not recorded when the highest signal was in force.

下表列出各站於熱帶氣旋警告信號生效時所錄得的最高 10 分鐘平均（持續）風速，留意此風速不一定於最高信號生效期間錄得。

Charts and Figures 各項數據

Table 1: Track data from HKWW:
表一 : 香港天氣觀測站之路徑資料

Table 2: Maximum gust and hourly average wind speed recorded in Hong Kong from HKO:
表二 : 香港天文台公佈的各站最高每小時平均風力和陣風數據 (英文)

Table 3: Rainfall (in millimetres) contributed by 17W from HKO (figures in brackets are based on incomplete hourly data):
表三 : 香港天文台公佈的各站雨量資料 (英文) (方括號內之數據由不完整之每小時資料擷取)

Last Accessed 最近訪問日期: Thu Jun 11 2026 11:56:49 HKT
Last Modified 最近修訂日期: Sat Apr 18 2026