Severe Thunderstorms on 20 and 21 July 2005

Severe Thunderstorms on 20 and 21 July 2005

The very hot weather in recent days saw daytime temperatures inland rising above 35 degrees. The increasingly unstable atmosphere led to active thunderstorm development.

Thunderstorms started to affect Hong Kong around 8 pm yesterday (20 July). The storms grew more intense as they passed over the territory. The Observatory's lightning location network recorded nearly 10,000 lightning strikes in the two-hour period leading up to midnight (Fig. 1). This is the highest number of strikes recorded in a thunderstorm event since the network became operational on 21 June this year. The Amber Rainstorm Warning was issued at 11 pm. Heavy rain lasted for several hours. More than 30 millimetres of rainfall fell generally over the territory, with part of Tsuen Wan and Tai Po areas recording rainfall amounts in excess of 100 millimetres.

Hong Kong was once again hit by squally thunderstorms this afternoon (21 July). Violent gusts of over 100 kilometres per hour were recorded at Black Point at about 4:30 pm. Between 4 pm and 6 pm, the lightning location network registered more than 1,800 lightning strikes. The Observatory also received reports of hail at Tsing Yi area at about 5 pm. Over the past 38 years (1967-2004), there were altogether 32 days with hail reports (Table 1), most of them in spring time (March and April). The last hail observation in Hong Kong was on 11 August 2004 at the Kadoorie Farm in Tai Po.

Table 1 Number of days with hail reports as received by the Observatory (1967-2004)

Up to 7 pm today (21 July), details of warnings issued by the Observatory are tabulated below:

Thunderstorm Warning:
20 July 7:55 pm - 21 July 5:30 am
21 July 8:15 am - 8:45 am
21 July 4:05 pm - 6:50 pm

Amber Rainstorm Warning:
20 July 11:00 pm - 21 July 1:35 am

Very Hot Weather Warning:
16 July 11:45 am - 21 July 4:30 pm

For information on Thunderstorm Warning and related precautionary measures, please refer to the following Observatory webpage:
http://www.weather.gov.hk/wservice/warning/thunder.htm

In the past month, the number of visits to the Observatory lightning location information webpage reached 265,000. Details on the lightning location information webpage can be found at:
http://www.weather.gov.hk/wxinfo/news/2005/pre0621e.htm

For the latest weather forecasts, please refer to the following Observatory webpages: http://www.weather.gov.hk/wxinfo/currwx/flw.htm (Local Weather Forecast) and http://www.weather.gov.hk/wxinfo/currwx/fnd.htm (7-day Weather Forecast)

Fig.1 Lightning strikes over Hong Kong from 10 pm to midnight on 20 July as recorded by the Observatory's Lightning Location Network.