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200813W (NURI) - Profile

(First issued on September 6th, 2008, final version issued on October 7th, 2008)

Brief profile of NURI:

JTWC number 13W
International number 0812
Period of existence 17 August, 2008 08 HKT to 23 August, 2008 02 HKT
Lifetime 5.75 days
Maximum 1-minute wind (JTWC) 100 knots
Minimum pressure (JTWC) 948 hPa
Highest TC signal by HKO (if applicable) 9 (Increasing Gale or Storm Signal)
Closest point of approach by HKO (if applicable) <1 km (real-time warnings: 1; 2* and TC report)
Time of closest approach by HKO (if applicable) 22 August, 2008 17-18 HKT (real-time warning*) / 22 August, 2008 17:20 HKT (TC report)
Lowest pressure recorded at HKO (if applicable) 982.3 hPa (22 August, 2008 15:46 to 16:12 HKT)

*The locations of NURI at 17 and 18 HKT are 22.3N 114.3E and 22.3N 114.1E respectively while the location of HKO is at 22.3N 114.2E. All measurements are correct to 1 decimal place.

TC signals for Hong Kong & Track:

Table:

Signal
Date and time
Distance from HK
Predicted movement
Max. 10-min winds
2008/08/20 (WED) 18:15 HKT
ESE 760 km
NW/WNW at 14 km/h
148 km/h (80 knots, CAT. 1)
2008/08/21 (THU) 20:40 HKT
SE 300 km
WNW at 14 km/h
121 km/h (65 knots, CAT. 1)
2008/08/22 (FRI) 07:40 HKT
SE 160 km
NW/WNW at 14 km/h
121 km/h (65 knots, CAT. 1)
2008/08/22 (FRI) 13:40 HKT
ESE 40 km
NW at 14 km/h
121 km/h (65 knots, CAT. 1)
2008/08/23 (SAT) 00:40 HKT
NW 100 km
NW/WNW at 14 km/h
103 km/h (55 knots, STS)
2008/08/23 (SAT) 02:40 HKT
WNW 130 km
WNW at 14 km/h
83 km/h (45 knots, TS)
2008/08/23 (SAT) 09:40 HKT
WNW 190 km
W at 16 km/h
56 km/h (30 knots, TD)
2008/08/23 (SAT) 11:15 HKT
NW 200 km
W at 16 km/h
56 km/h (30 knots, TD)

Figure: (Track courtesy of Lorenzo. Data from HKO.)

TC Track

IR imagery animation 紅外線雲圖動畫:

TC track from HKWW:

TC Track

TC tracks from HKO:

Past HKWW Bulletins on NURI

Please click here for bulletins on NURI.

Storm Formation

NURI was again a storm (after FENGSHEN) that major agencies failed to predict its movement with an early recurvature that did not realize at all.

Under favorable environment, tropical disturbance 92W in northwestern Pacific Ocean developed into a tropical depression on August 17th. JTWC formally recognized this depression at 08 HKT that day and the depression was given the temporary number 13W. The JMA released gale warning for this system later at 20 HKT the same day, and upgraded it to a tropical storm the next day at 08 HKT, assigning the name NURI which is contributed by Malaysia. For the HKO, it upgraded the system to tropical depression and tropical storm status at 05 and 08 HKT on August 18th respectively.

At that time, the western extension of a subtropical ridge was firmly positioned north of the system, and the ridge was forecast to extend westward in the next two to three days. However, numerical models called for a sharp retreat of the ridge three days later, leading to a NW to N movement later on as depicted in most agencies' initial forecasts.

Figure 1 - Steering chart at 14 HKT, August 18th

Figures 2a to d - Initlal forecast tracks of NURI by various agencies (JTWC, CWB, HKO and JMA in order)

Figure 3 - Image of NURI at 14:30 HKT on August 17th

Storm Development

The subtropical ridge remained intact in the next few days, extending westward at the same time which was in agreement with the situation projected by models. Indeed, the 500 hPa geopotential height near the centres of the high pressures remained above 5,900 metres before NURI crossed the Luzon Strait. As this strong ridge was positioned to the north of the system, NURI moved quickly westward to west-northwestward in the next three days, at a speed between 13 and 18 knots (24 and 33 km/h). It skirted past the northern tip of Luzon on August 20th and made its way into the South China Sea.

Figure 4 - Steering chart at 14 HKT, August 20th

Figures 5a to d - Forecast track of NURI by various agencies (JTWC, CWB, HKO and JMA in order) at 14 HKT on August 20th

As for NURI's intensity, it benefited from good equatorward outflow and high water heat content and intensified successively into a severe tropical storm and a typhoon at 20 HKT on August 18th and 02 HKT on August 19th respectively (JMA 10-minute standard). It reached peak intensity as it crossed Luzon Strait as a category 3 typhoon (100 knots [185 km/h] in JTWC 1-minute standard**). NURI caused some damages to the northern provinces of the Philippines; 12 people were killed, 13 injured and 17 went missing as a result of the storm. Widespread heavy rain was observed in the whole Luzon.

** Revised upward from 95 knots.

Figure 6 - NURI at peak intensity

NURI in the South China Sea and Preparations in Hong Kong

As a result of land interactions with the Philippine terrain, NURI moved nearly due west just before crossing Luzon Strait, and a northwestern movement was observed briefly as it moved into the South China Sea. The ridge started to weaken at this time, and this slowed down NURI's movement. This decelerated NW movement, together with anticipated gradual weakening of the subtropical ridge, prompted agencies to adjust the location of landfall further to the east. However, as land interaction diminished and the strength of the ridge in China was maintained, NURI moved due west again in the small hours on August 21st and agencies subsequently turned their tracks westward, depicting a landfall in the vicinity of Hong Kong in the afternoon forecasts (on August 21st).

As NURI came within 800 km of Hong Kong, the HKO issued the Standby Signal number 1 at 18:15 HKT on August 20th when NURI was 760 km ESE of the territory. Vertical wind shear in the South China Sea has strengthened significantly since NURI neared Luzon due to the diminishing influence of the subtropical ridge. NURI failed to gain strength as predicted earlier, but still it was a significant tropical cyclone that was threatening the South China coast.

NURI's strength fluctuated during the later parts of August 20th and in the morning of August 21st, but eventually succumbed to the strong shear to begin its weakening trend. NURI maintained a stable WNW movement for the rest of August 21st, and the Observatory raised the alert to the Strong Wind Signal number 3 at 20:40 HKT on the same day. This Strong Wind Signal was again deemed precautionary as winds in the territory did not reach strong force levels before August 22nd. Since the HKO started to predict a direct hit, significantly heightened alert was observed among the general public since the afternoon of August 21st. Services at cargo terminal were suspended (Chinese link) and the HKO indicated in the tropical cyclone bulletin that "the chance of the Gale or Storm Signal number 8 cannot be ruled out" but was unlikely during the early morning.

(left) Figure 7 - Vertical wind shear in the South China Sea at 14 HKT, August 21st
(right) Figure 8 - HKO's direct hit prediction at 16 HKT, August 21st

Figure 9 - Forecasts by various agencies, 14 HKT August 21st. The pink and pale red regions indicate 50% (or above) probability of gales in Victoria Harbour for typhoons and severe tropical storms respectively.

Winds picked up after midnight on August 22nd, and by sunrise winds reached strong force in urban areas and gale force on high grounds and in offshore waters. The Observatory issued the Pre-no. 8 Special Announcement at 05:50 HKT when the storm was 190 km SE of Hong Kong, indicating that the number 8 signal would be issued before 08 HKT. Ferry services within the territory and those between Hong Kong and Macau were gradually suspended in the morning and all day schools were also suspended on August 22nd.

The Observatory issued the Number 8 Northwest Gale or Storm Signal at 07:40 HKT when NURI was 160 km SE of Hong Kong, and stated that the chance of a direct hit could not be ruled out.

Direct Hit on Hong Kong

Pressure dropped sharply during the morning of August 22nd. Being the closest available station to NURI, Waglan Island's sea level pressure dropped to 989 hPa near 09 HKT and further to 985 hPa at 11 HKT. North to northwesterly winds continued to strengthen in the territory with a direct hit becoming more and more likely. In light of this situation, the Observatory issued the Increasing Gale or Storm Signal number 9 at 13:40 HKT, the first issuance since Typhoon Dujuan in 2003. Storm force winds were recorded at several stations at that time with the storm being 40 km away from the HKO Headquarters. In a media interview with Edwin Ginn, Senior Scientific Officer of the HKO, it was mentioned that the chance of the Hurricane Signal number 10 could not be ruled out if NURI edged closer and maintained intensity.

However real-time wind speed data were not sufficient to support hurricane force winds within Hong Kong at sea level, and thus the HKO downgraded NURI into a severe tropical storm at 17 HKT, literally wiping out the chance of the hurricane signal. In the next hour, NURI turned to a westerly motion and traversed Kowloon from east to west, entering the seas between Hong Kong Island and Tsing Yi. NURI then turned northwestward and approached Tuen Mun at near 20 HKT, and went north into Deep Bay at 21 HKT. It skirted the western part of Shenzhen and crossed the Pearl River estuary to the western coast, weakening gradually in the meantime.

During the passage of NURI, winds subsided in some urban areas but was later on replaced by strong southwesterly winds. Waglan Island (with elevation in excess of 80 m) recorded hurricane force southwesterly winds as NURI moved to northwestern parts of Hong Kong, and Cheung Chau recorded storm force winds. Therefore the number 9 signal was justified as it alerted the public about the rapidly strengthening winds at night.

The following table shows the location of NURI between 14 HKT and 23 HKT on August 22nd (Coordinates extracted from HKO tropical cyclone bulletins):

Time (on August 22nd)
Coordinates
Bearing and distance from HKO
Location
14 HKT
22.1N 114.5E
ESE 40 km
---
15 HKT
22.3N 114.4E
E 20 km
Seas near Sai Kung
16 HKT
22.3N 114.4E
E 20 km
Seas near Sai Kung
17 HKT
22.3N 114.3E
E 15 km
Sai Kung
18 HKT
22.3N 114.1E
W 10 km
Seas between HK Island and Tsing Yi
19 HKT
22.3N 114.0E
W 20 km
Northeastern corner of Lantau Island
20 HKT
22.4N 114.0E
WNW 20 km
Tuen Mun
21 HKT
22.5N 114.0E
NW 30 km
Deep Bay
22 HKT
22.6N 113.9E
NW 40 km
Western Shenzhen
23 HKT
22.7N 113.6E
NW 70 km
Northwestern corner of Pearl River estuary

It is worth noting that if the intermediate positions are linearly interpolated, it will represent a direct hit on the Observatory (22.3N 114.2E correct to 1 decimal place). In HKO's report on Nuri, Nuri passed Tsim Sha Tsui and was closest to the Observatory at 17:20 HKT when it was less than 1 kilometre south of the headquarters.

Figures 10a to e - Wind speed time series for Cheung Chau, Green Island, Peng Chau, Tsing Yi (Shell Oil Depot) and Waglan Island respectively

Figure 11 - NURI near landfall at Hong Kong

Figures 12a to g - RADAR images from 00 HKT August 22nd to 00 HKT August 23rd at 4-hour intervals.

Figure 13 - NURI's track near Hong Kong

Figures 14a to c - Mean sea level pressure during August 22nd at Cheung Chau, HKO and Waglan Island respectively

Figures 15a to g - Wind directions and speeds in Hong Kong from 00 HKT August 22nd to 00 HKT August 23rd, at 4-hour intervals.

Figure 16 - Judging from this wind distribution image, the centre of NURI should be very close to the Observatory at 17:10 HKT

NURI's Weakening and Dissipation

NURI travelled WNW and skirted Guangzhou near midnight, August 23rd. Due to greatly reduced water content, NURI weakened rapidly and the Observatory downgraded NURI into a tropical storm, tropical depression and finally an area of low pressure at 02 HKT, 09 HKT and 13 HKT respectively.

As for tropical cyclone signals, the Observatory replaced the number 9 signal with the number 8 Southwest Gale or Storm Signal at 00:40 HKT on August 23rd as wind speeds ceased to be "increasing". It was lowered to the Strong Wind Signal number 3 at 02:40 HKT when gales were confined on high grounds and offshore waters. The Standby Signal number 1 was issued at 09:40 HKT as gales faded away in the territory, and all signals were cancelled at 11:15 HKT when NURI no longer posed a threat to Hong Kong.

There are two points that are worth mentioning concerning the approach of NURI:

  1. NURI made landfall on Hong Kong instead of skirting south of the territory. As the large centre of NURI passed over Hong Kong winds were relatively light. If instead NURI swept past the southern Hong Kong waters, Hong Kong would be affected by the easterly winds in NURI's northern circulation. As most places in Hong Kong are exposed to the east and Hong Kong would then be inside the "dangerous" semicircle of the storm, winds could be considerably higher and the Hurricane Signal might would have been necessary in that case.
  2. NURI's strongest rainbands were in its southern semicircle. If NURI continued to travel north after traversing Hong Kong those rainbands would approach the territory and the squalls that accompanied the rainbands might push wind speeds much higher than that actually observed as NURI moved into the Pearl River estuary. Therefore in the case of NURI, Hong Kong avoided the dangerous easterly winds when it was approaching, and also avoided the squalls when it was leaving.
Incidents Related to NURI

Three issues arose as NURI affected Hong Kong:

  1. On August 21st, emails regarding the exact times that different tropical cyclone signals were to be issued spread all over Hong Kong, and SMS's about the same information were sent throughout the territory. The message was, of course, fake and the Observatory stated that they did not release anything of this kind to any organization. They advised the public to refer to official reports disseminated through radio stations, TV stations and the Observatory's website. [Link to the relevant news (in Chinese)]


    Figure 17 - The fake SMS message

  2. The use of the word "qingchen" (lit. "clear morning") to represent times in the region between 1 a.m. and 5 a.m. The word "qingchen" in Chinese has evolved from meaning the early hours after midnight to representing times near sunrise, and therefore ambiguity exists and people may interpret this word in different ways. The Observatory has therefore agreed to abandon this word together with the English counterpart "early morning", and will use the word "lingchen" in Chinese and "in the small hours" in English to represent times between midnight and sunrise. Please click the following links to read more on this:
  3. Several pictures that claimed to be the "eye" of NURI were taken by enthusiasts in the eastern part of Hong Kong when NURI passed in its vicinity. However, as NURI was not a strong system and its centre was very unclear and cloud-filled in satellite imageries as it approached Hong Kong, it would be better to describe the blue sky in those photos a clear region within the centre, and it would be technically unsuitable to describe it as an eye. Nevertheless, NURI was one of the strongest systems that crossed Hong Kong in the daytime since 2000, and the rarity of such photos have prompted the Observatory to include one in its tropical cyclone report. [Link to the relevant news (in Chinese, accessible using HK IP addresses only)]


    Figure 18 - Blue "eye" within the centre of NURI (click on the above link for the news article from Apple Daily)
Charts and Figures

Table 1: Track data from HKWW:

YYMMDDZZ Lat Long Wind
08081700 145N1400E 025
08081706 156N1387E 030
08081712 160N1369E 035
08081718 160N1350E 040
08081800 160N1333E 045
08081806 160N1317E 050
08081812 165N1299E 065
08081818 169N1283E 070
08081900 171N1268E 080
08081906 176N1254E 090
08081912 181N1243E 095
08081918 184N1227E 090
08082000 187N1218E 095
08082006 189N1211E 095
08082012 195N1205E 080
08082018 200N1191E 080
08082100 201N1180E 080
08082106 203N1173E 080
08082112 206N1165E 070
08082118 209N1159E 070
08082121 211N1157E 070
08082200 214N1154E 070
08082203 218N1149E 070
08082206 221N1145E 065
08082207 222N1144E 065
08082208 223N1144E 065
08082209 223N1143E 065
08082210 223N1141E 065
08082211 223N1140E 065
08082212 224N1140E 060
08082215 227N1136E 055
08082218 228N1132E 050
08082300 231N1127E 040

Table 2: Maximum gust and 60-minute average wind speed recorded in Hong Kong from HKO:

Station Maximum Gust Maximum Hourly Wind
Direction Speed (km/h) Date/Month Time Direction Speed (km/h) Date/Month Time
Bluff Head (Stanley) SSW 118 22/8 19:54 SSW 75 22/8 20:00
Central Pier WNW 90 22/8 11:44 NW 43 22/8 12:00
Cheung Chau SSW 126 22/8 22:18 SSW 88 22/8 23:00
Cheung Sha Wan  SW 96 23/8 00:10 SW 54 22/8 21:00
Green Island SSW 144 22/8 23:06 SW 110 22/8 21:00
Hong Kong International Airport SSW 112 23/8 01:11 SSW 76 23/8 01:00
Kai Tak N 118 22/8 13:08 N 47 22/8 13:00
King's Park  NNE 118 22/8 10:51 SSW 49 22/8 21:00
Lau Fau Shan N 92 22/8 08:28 N 49 22/8 09:00
Ngong Ping SW 196  22/8 23:31 SW 128 23/8 01:00
North Point NNE 110 22/8 12:02 NNE 54 22/8 14:00
Peng Chau N 112  22/8 10:32 NNW 62 22/8 12:00
NNW 62 22/8 14:00
Ping Chau ENE 108  22/8 13:32 E 34 22/8 15:00
Sai Kung  NNE 148 22/8 13:33 NNE 87 22/8 14:00
Sha Chau NNW 128  22/8 12:36 N 94 22/8 15:00
SSW 128  23/8 01:12
Sha Lo Wan SW 135 23/8 01:10 SW 65 23/8 02:00
Sha Tin SW 101 22/8 21:27 SSW 45 22/8 21:00
Shek Kong NNE 76 22/8 14:10 N 38 22/8 15:00
Star Ferry (Kowloon) WSW 104 22/8 20:00 S 34 22/8 21:00
SW 104 22/8 21:12
Ta Kwu Ling  NNE 87 22/8 13:26 N 40 22/8 14:00
Tai Mei Tuk SW 144 22/8 20:25 NE 79 22/8 14:00
Tai Mo Shan SSW 144 22/8 20:53 N 96 22/8 13:00
Tap Mun NE 121 22/8 13:33 NE 62 22/8 14:00
Tate's Cairn  N 193 22/8 13:45 N 122 22/8 14:00
Tsak Yue Wu NNE 106 22/8 11:48 NNE 45 22/8 12:00
Tseung Kwan O N 90 22/8 12:08 N 31 22/8 13:00
Tsing Yi Shell Oil Depot NNW 101 22/8 10:06 NNW 56 22/8 13:00
Tuen Mun Government Offices SSW 96 23/8 02:39 S 36 23/8 01:00
S 36 23/8 02:00
Waglan Island SSW 157 22/8 19:32 SSW 115 22/8 20:00
Wetland Park N 94  22/8 12:08 N 41 22/8 14:00
Wong Chuk Hang N 88 22/8 11:32 NNW 31 22/8 13:00

Table 3: Rainfall contributed by NURI from HKO (figures in brackets are based on incomplete hourly data):

Station   20 Aug 21 Aug 22 Aug 23 Aug Total
Hong Kong  Observatory 0.0 Trace 61.6 36.9 98.5
Cheung Chau (CCH) 0.0 0.0 34.5 15.0 49.5
Hong Kong International Airport (HKA) 0.0 Trace 69.8 34.9 104.7
H12 Mid Levels [0.0] [0.0] [47.0] [39.0] [86.0]
H19 Shau Kei Wan 0.0 0.0 53.0 38.0 91.0
H21 Repulse Bay 0.0 0.0 20.5 29.5 50.0
K04 Jordan Valley [0.0] [0.0] [56.5] [29.5] [86.0]
K06 So Uk Estate [0.0] [0.0] [51.0] [26.0] [77.0]
N05 Fanling 0.0 0.0 21.5 23.0 44.5
N06 Kwai Chung 0.0 0.0 49.0 35.0 84.0
N09 Sha Tin [0.0] [0.0] [58.0] 36.5 [94.5]
N12 Yuen Long 0.0 0.0 26.0 20.0 46.0
N13 High Island 0.0 0.0 40.5 24.0 64.5
N17 Tung Chung 0.0 0.0 106.0 66.5 172.5
R21 Tap Shek Kok 0.0 5.5 26.0 19.5 51.0
R26 Shek Kong 0.0 0.0 33.5 18.5 52.0
R31 Tai Mei Tuk 0.0 0.0 35.0 15.0 50.0

Last Accessed: Mon Aug 26 2019 02:54:11 HKT
Last Modified: Sun Oct 02 2016

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