What is the main feature of the Location-specific Lightning Alert Webpage (LLAW)?
The Location-specific Lightning Alert Webpage can help you monitor the lightning activities in your location or other location of interest. Users can simply select the location of interest and choose a circular range around the location in the webpage. An alert will be given automatically when lightning is detected within the specified region.
Please click "OK" button once to init an audio alert function.
Please enter the address or name of building to search a location.
For example: NATHAN ROAD 134A or HONG KONG OBSERVATORY
Click on the map and drag the mouse to draw a line, release the mouse to finish.
Click two points on the map to calculate the distance between them.
Click on the map to draw up a polygonal region. Double-click to complete the action. The number of
lightning strokes detected in the region will be displayed in a new window.
Number of lightning strokes within the polygon:
* Angle measure in clockwise direction from the start point
Points to Note:
The Location-specific Lightning Alert Webpage (LLAW) includes more selectable options on outdoor activity venues and geographical information which could help you monitor conveniently the lightning activities in the vicinity of your location. This service is particularly useful for managers of outdoor activity venues. In the Enhanced LLAW, the location of interest for lightning alert is extended to cover the Pearl River Delta region.
The LLAW map shows cloud-to-ground or cloud-to-cloud lightning strokes over Hong Kong and its vicinity as detected by the Lightning Location Network. The lightning records will be updated at 5-minute intervals. Cloud-to-cloud lightning strokes are those detected strokes that did not reach the ground. As such, they might not affect people or facilities on the ground. However, it should be noted that they may sometimes precede cloud-to-ground strokes. The location as shown depicts roughly the starting point of the discharge from one cloud to the other.
Selectable options for lightning alert function are available at the top of the map in the webpage. You can click directly on the map to select your location of interest. You can also select your location from a list of predefined places from the “Outdoor Activities Location” option. After confirming your location of interest, you can define your alert range according to your need at the “Lighting Alert Function & Other Options”.
The LLAW map can be zoomed into street level so that the lightning symbol may be displayed over a street or a building, and zoomed out to show southern China and the northern part of South China Sea. Please note that the actual location of the lightning stroke may be more than several hundred metres away from the displayed position and the Lightning Location Information System could only detect and display lightning strokes over Hong Kong and its vicinity.
You can overlay radar images on the map. Radar images with 64-km range update once every 6 minutes while images with 128-km and 256-km range update once every 12 minutes. The rainfall rates as estimated from radar data are represented by different colours. Since the measurements of radar and lightning location system differ in both time and space, the location of lightning may not correlate exactly with that of rain area in the radar image. For details about the radar images, please refer to the main pages of Weather Radar Image.
The Lightning Location Network comprises seven stations jointly established by the Hong Kong Observatory, the Guangdong Meteorological Bureau and the Macao Meteorological and Geophysical Bureau. The stations are located at Chung Hom Kok, Tsim Bei Tsui, Sha Tau Kok in Hong Kong, Sanshui, Huidong and Yangjiang in Guangdong, as well as Taipa in Macao. (Click here to see the location of these stations)
The Observatory has enhanced the Lightning Location Information System with new computer hardware and software. The enhanced system was put into operation at end May 2017. The accuracy of the enhanced system in determining the location of cloud-to-ground lightning strokes is about 200 to 300 m within the network when all stations are operative. The lightning detection efficiency, i.e. the probability that a stroke with peak current greater than a certain level can be detected by the network, is estimated to be more than 90%. The efficiency of cloud-to-cloud lightning detection is roughly 50%. The location accuracy and detection efficiency will be reduced when the lightning stroke occurs outside of the network or when not all of the stations are operative.
There may be some cases that not all occurred lightning strokes can be detected and there may also be false detection of lightning strokes. As it takes time for communication and computation, there is a delay of a few minutes in the display of data. Other factors, including interruption to telecommunications services and power supply, can also affect the reliability and availability of the lightning information.