|201912W (BAILU 白鹿) - Profile 檔案|
(First draft issued on August 29, 2019)
(初稿於 2019 年 8 月 29 日發出)
Brief profile of BAILU | 白鹿小檔案:
|JTWC number 聯合颱風警報中心 (JTWC) 號碼||12W|
|International number 國際編號||1911|
|Period of existence 生存時期 (JTWC)||2019/08/21 14 HKT - 2019/08/26 08 HKT|
|Lifetime 壽命 (JTWC)||4.75 days 日|
|Maximum 1-minute wind (JTWC) JTWC 一分鐘平均最高中心風速||55 knots 節 (Severe Tropical Storm 強烈熱帶風暴)|
|Minimum pressure (JTWC) JTWC 最低氣壓||982 hPa 百帕|
|Highest TC signal by HKO
|1 (Standby Signal 戒備信號)|
|Closest point of approach by HKO
|Time of closest approach by HKO
|Lowest pressure recorded at HKO
TC signals in Hong Kong* 香港曾經生效的熱帶氣旋警告*:
|Date and time
|Distance from HK
|Max. 10-min winds
|2019/08/24 (SAT) 14:40 HKT||E 650 km||NW at 28 km/h||105 km/h (55 knots, STS)|
|2019/08/25 (SUN) 19:20 HKT||N 280 km||WNW at 20 km/h||55 km/h (30 knots, TD)|
*Based on the information from real-time tropical cyclone warning bulletins.
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 tracks from HKO 天文台的熱帶氣旋路徑圖:
|Past HKWW Bulletins 本站發佈|
|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)
BAILU developed as tropical disturbance 97W in the northwest Pacific east of the Philippines in mid-August. The convective patch showed signs of development on August 20, and the JTWC issued a tropical cyclone formation alert that afternoon. At the same time, the JMA issued a gale warning for the system.
On August 21, 97W developed further with spiraling cloud bands expanding around its centre. The JTWC upgraded 97W into tropical depression 12W in the afternoon, while the JMA even upgraded it into tropical storm status and named it BAILU. After the system was named, the HKO upgraded BAILU into a tropical depression later that afternoon. At its formation, the centre of the subtropical ridge was positioned in the seas southeast of Japan. BAILU was expected to move northwest along the southwestern periphery of the ridge, and would likely impact Taiwan several days later.
BAILU organized itself gradually on August 22, and moved more westwards than projected as most of its convections were concentrated in its southwestern quadrant. Nevertheless, it started to pick up speed towards the northwest that afternoon. Due its previous westward track, various official agencies revised their forecasts and predicted a landfall in southern Taiwan or even no landfall there at all.
BAILU strengthened into a severe tropical storm early on August 23. As vertical wind shear relaxed, BAILU became more symmetric over the day with tight cloud bands encircling it. Following a slight deflection towards the west-northwest, it made landfall briefly in the southern tip of Taiwan in the afternoon of August 24, and entered the Taiwan Strait soon after. BAILU's northern convections were affected by Taiwan's terrain and the storm centre moved erratically that night.
After moving west for several hours in the night of August 24, BAILU deflected to the northwest again and made its final landfall near Dongshan, Fujian at around 7:30 am August 25. It weakened into a tropical storm soon after while moving west-northwest that day, entering northern Guangdong. It continued to weaken on land and degraded into an area of low pressure early on August 26 near Shaoguan, Guangdong.
白鹿的前身為熱帶擾動 97W，於 8 月中旬在菲律賓以東的西北太平洋形成。97W 的對流雲團於 20 日有跡象發展，聯合颱風警報中心於當天下午對其發佈熱帶氣旋形成警報。與此同時，日本氣象廳則發出烈風警報。
97W 於 21 日進一步發展，螺旋雲帶於中心周圍擴展。聯合颱風警報中心於下午升格 97W 為熱帶低氣壓 12W，而日本氣象廳更將其升格為熱帶風暴，命名為白鹿。系統被命名後，香港天文台將白鹿升格為熱帶低氣壓。白鹿形成初期，副熱帶高壓脊中心位於日本東南方海域，預期白鹿將沿該脊西南部向西北移動，或於數日後登陸台灣。
白鹿於 22 日逐漸組織其對流，由於大部分對流集中在西南象限，風暴移向比預期偏西，但終於在當天下午加速向西北移動。因為其先前偏西的路徑，各官方氣象台均更新其預測路徑，指白鹿將登陸台灣南部甚至不登陸台灣。
白鹿於 23 日初段增強為強烈熱帶風暴。隨著垂直風切變減弱，日間白鹿的結構變得更為對稱，周邊各方向皆有緊密雲帶。白鹿的路徑向西北偏西偏折，於 24 日下午短暫登陸台灣南端，隨後進入台灣海峽。由於白鹿北面的對流受台灣地形影響，白鹿中心當晚移動較不規則。
24 日晚間白鹿曾有數小時向西移動，但其後再度轉向西北，並於 25 日早上約 7 時 30 分登陸福建東山縣。登陸後不久，白鹿減弱為熱帶風暴，日間向西北偏西移動並進入廣東北部。它繼續於陸上減弱，於 26 日早段在廣東韶關市一帶減弱為低壓區。
|Weather in Hong Kong During Approach 風暴影響時香港天氣狀況|
Locally, it was very hot on August 24 as the subsidence associated with BAILU resulted in generally fine and hazy weather in southern China. The HKO issued the #1 Standby Signal at 2:40 pm when BAILU was about 650 km east of Hong Kong. Later that night, the HKO mentioned that the chances for higher signals were not high unless BAILU moved closer to the Pearl River Estuary than expected, and that strong winds might be observed offshore.
As BAILU approached southeastern China, an intense rainband in BAILU's outer circulation reached Hong Kong just after midnight August 25. The Amber Rainstorm Warning was issued at 12:50 am, and remained in force until 2:40 am. Heavy thunderstorms struck various parts of the territory, and the associated squalls yielded a sharp spike in wind speeds. Winds at Cheung Chau and Green Island reached gale force for a brief moment during 1-2 am, and those at several other locations such at Chek Lap Kok reached strong force. Later that day, the HKO said that more than 4000 cloud-to-ground lightning strikes were recorded within the territory during the day.
The precipitation diminished after 2 am, after the rainband had passed. As BAILU edged closer, more persistent rainfall resumed in the early morning. The Amber Rainstorm Warning was issued the second time at 11:30 am, which lasted until 2:45 pm. The HKO downgraded BAILU into a tropical depression in the afternoon; the #1 Standby Signal was cancelled at 7:20 pm when the storm was around 280 km north of the territory.
A long, narrow band of intense convections developed near the coastal areas towards midnight August 26, at about the time when BAILU was the closest to Hong Kong. The Amber Rainstorm Warning was issued again at 11:55 pm August 25. Heavy rainfall persisted over most of Hong Kong; the Warning was upgraded to red at 12:40 am August 26. In the hour between 12:45 and 1:45 am, some rainfall gauges in Sai Kung, Tai Po, Islands District, Southern District, Central & Western District and Wanchai registered more than 50 mm of rain, the threshold for the Red Rainstorm Warning; 9 of the remaining 12 districts had gauges receiving more than 30 mm of rain. In response to the persistent heavy rain, the Landslip Warning was issued at 2:50 am and remained in force until 9:55 pm that day. The rainband weakened soon after 3 am and the Red Rainstorm Warning was replaced by the Amber warning at 3:25 am. The Amber Rainstorm Warning was later cancelled at 5 am.
Although BAILU moved away gradually during the day, the weather remained unstable throughout August 26 with occasional squally showers. A total of 88.4 and 178.3 mm of rainfall was recorded at the HKO on August 25 and 26, respectively.
與白鹿相關的下沉氣流於 8 月 24 日影響華南。本港方面，24 日大致天晴，天氣酷熱並有煙霞。香港天文台於下午 2 時 40 分發出一號戒備信號，當時白鹿於香港以東約 650 公里。當晚，天文台表示除非白鹿比預期更接近珠江口，否則改發更高信號機會不大，而離岸或吹強風。
隨著白鹿靠近中國東南部，白鹿外圍環流中的一條強雨帶於 25 日午夜過後到達香港。天文台於上午 12 時 50 分發出黃色暴雨警告，至上午 2 時 40 分取消。強雨帶影響期間，本港多區有猛烈閃電及雷暴，相關狂風令風速短暫急速上升。長洲及青洲於上午 1 至 2 時曾錄得烈風，而赤鱲角等數個氣象站吹強風。其後，天文台表示當天境內共錄得超過 4000 次雲對地閃電。
雨帶過後，本港雨勢於上午 2 時後減弱。隨著白鹿進一步靠近，早上開始雨勢變得持續。黃色暴雨警告於上午 11 時 30 分第二次發出，並持續至下午 2 時 45 分。天文台於下午將白鹿降格為熱帶低氣壓，而一號戒備信號於下午 7 時 20 分取消，當時白鹿位於香港以北約 280 公里。
至 26 日接近午夜時份，一條窄長的強雨帶於沿岸地區發展，當時白鹿最為接近香港。天文台於 25 日下午 11 時 55 分再度發出黃色暴雨警告。大雨於香港多區持續，暴雨警告於 26 日上午 12 時 40 分改為紅色。在上午 12 時 45 分至 1 時 45 分的一小時間，西貢、大埔、離島、南區、中西區及灣仔錄得超過 50 毫米、即紅色暴雨警告所示雨量，而其餘 12 區中有 9 區錄得超過 30 毫米雨量。因應豪雨持續，天文台於上午 2 時 50 分發出山泥傾瀉警告，維持至下午 9 時 55 分才取消。雨帶於上午 3 時後減弱，紅色暴雨警告於上午 3 時 25 分被黃色暴雨警告取代，而後者亦於上午 5 時取消。
雖然白鹿於 26 日日間逐漸遠離，但當日天氣仍然不穩定，間中有狂風驟雨。天文台於 25 及 26 日分別錄得 88.4 及 178.3 毫米雨量。
|Image Gallery 圖片庫|
Figure 1 - Satellite image of BAILU during its initial stages of formation
圖 1 - 白鹿形成初期之衛星雲圖
Figure 2 - Forecast tracks from various official agencies on August 21 (left) and August 23 (right)
圖 2 - 8 月 21 日 (左) 及 23 日 (右) 各官方氣象台之預測路徑
Figure 3 - Steering flow chart at 8 am August 23
圖 3 - 8 月 23 日上午 8 時之駛流場圖
Figure 4 - Wind field analysis at 8:32 am August 23 (left) and 9:46 pm August 24 (right)
圖 4 - 8 月 23 日上午 8 時 32 分 (左) 及 24 日下午 9 時 46 分 (右) 之風場掃描圖
Figure 5 - BAILU's appearance on radar prior to its landfall at Taiwan
圖 5 - 白鹿登陸台灣前之雷達圖
Figure 6 - Satellite image of BAILU at peak intensity
圖 6 - 白鹿於巔峰強度時之衛星雲圖
Figure 7 - Radar image at 1:24 am August 25 (left) and close-up image with lightning locations overlaid (right)
圖 7 - 8 月 25 日上午 1 時 24 分之雷達圖 (左) 及附閃電位置之放大圖 (右)
Figure 8 - Wind speed time series at Chek Lap Kok (top) and Cheung Chau Beach (bottom) between August 24 and August 25
圖 8 - 赤鱲角 (上) 及長洲泳灘 (下) 於 8 月 24 至 25 日之風速時間序列圖
Figure 9 - Radar image showing the intense rainband that affected Hong Kong near midnight August 26
圖 9 - 雷達圖顯示 8 月 26 日近凌晨時份香港受強雨帶影響
Figure 10 - Minimum air temperatures on August 26 as of 1:20 am the same day. The temperature at the HKO dipped to 22.9 degrees amid torrential rain.
圖 10 - 截至 8 月 26 日上午 1 時 20 分之當日最低氣溫，天文台在傾盆大雨下溫度下降至 22.9 度
Figure 11 - Rainfall distribution maps for August 25 (left) and August 26 (right)
圖 11 - 8 月 25 日 (左) 及 26 日 (右) 之雨量分佈圖
|Winds Recorded at Reference Stations 參考站所錄得的風速|
Except for special cases, this section is not available for cyclones that only necessitated the Standby Signal. 除非特別情況，否則此部只當氣旋令天文台發出三號或更高信號時提供。
|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
YYMMDDZZ Lat Long Wind
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 BAILU 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: Sat Sep 21 2019 08:24:05 HKT
Last Modified 最近修訂日期: Thu Aug 29 2019