The Weather of October 2010

     The mean temperature for October 2010 was 24.8 degrees, 0.5 degrees below normal.  It was attributed to an intense northeast monsoon dominating over southern China during the last six days of the month.  The minimum temperature of 15.7 degrees recorded on 28 October was the lowest in October since 1988.

     Due to the prevalence of a dry continental airstream in the latter part of the month, October 2010 was also drier than usual.  The total rainfall in the month was 22.7 millimetres, only about 15 percent of the normal figure of 151.9 millimetres.  However, the accumulated rainfall since 1 January was 2311.1 millimetres, close to the normal figure of 2313.1 millimetres for the same period. 

     Under the influence of a fresh northeast monsoon, the weather was mainly fine for the first four days of the month.  A tropical depression developed near Hainan Island on 5 October and moved slowly for the next two days.  It weakened into an area of low pressure on 7 October.  The outer rainbands associated with the tropical depression and its remnant affected the south China coast and the northern part of the South China Sea, bringing cloudy weather and rain patches to the territory from 5 to 9 October. 

     With the establishment of a ridge of high pressure over southeastern China, easterly winds strengthened and brought rainy weather to Hong Kong on 10 October.  It remained windy with some rain the next day.  With the moderation of the easterly winds, local weather was sunny from 12 to 14 October.  Meanwhile, a cold front formed over northern Guangdong on 14 October and crossed the coastal areas of Guangdong the next morning.  Local weather turned slightly cooler and there were some rain over the territory on 15 and 16 October.  The northeast monsoon brought mainly fine and dry weather for the ensuing four days.

     Meanwhile, Super Typhoon Megi developed over the western North Pacific.  It weakened into a severe typhoon while crossing the Philippines on 18 October.  After entering the South China Sea, Megi drifted generally westwards on 19 October and turned northwards the next day, moving towards the south China coast. Under the combined effect of the northeast monsoon and Megi, local weather became cloudy with showers and there were fresh to strong gusty northerly winds with occasional gales on high ground on 21 October.  While Megi skirted about 400 kilometres east of Hong Kong and weakened into a typhoon, local winds moderated gradually and it remained cloudy with showers on 22 October. 

     Dominated by a dry continental airstream, the weather in Hong Kong turned mainly fine and dry for the ensuing three days.  An intense northeast monsoon reached the south China coast on the morning of 26 October.  Affected by the intense northeast monsoon, local temperature dropped progressively, decreasing to a minimum of 15.7 degrees on 28 October, the lowest of the month.  The weather was fine and very dry with occasional strong winds on high ground and offshore on 27 and 28 October.  Cool and very dry conditions persisted for the last 3 days of the month.

     Four tropical cyclones occurred over the western North Pacific and the South China Sea in the month. 

     Details of issuance and cancellation of various warnings/signals in the month are summarized in Tables 1.1 to 1.4.  Monthly meteorological figures and departures from normal for October are tabulated in Table 2.