The year 2003 was the fifth warmest year since records began in 1884. The mean temperature, 23.6 degrees, was 0.6 degrees above normal. It was largely due to milder weather in the first few months of 2003 when there were more sunshine and less frequent cold surges than normal. The year was also relatively dry, with rainfall about 12 per cent below normal. July 2003 was the driest July on record, with only about one third of the normal amount of rainfall for July. This exceptionally dry month was the main contributing factor of the below-normal annual rainfall. The very dry weather in July was associated with the ridge of high pressure over the Pacific being exceptionally strong and extending west to cover south China, bringing a long spell of fine weather to Hong Kong from late June to late July.
The number of tropical cyclones occurring in the western North Pacific in 2003 was less than normal. In Hong Kong, the tropical cyclone season started late in the year. The first tropical cyclone warning signal was issued on July 20, a month later than normal. Only 4 tropical cyclones, against the mean of 6, necessitated the issuance of tropical cyclone warnings locally.
In contrast to 2002 in which no tropical cyclone entered the South China Sea from the western Pacific, all tropical cyclones that affected Hong Kong in 2003 originated from the Pacific. This was likely to be a result of the change in atmospheric flow associated with the decay of El Nino during the year.
January was sunnier and slightly warmer than usual.
It was warmer and drier than usual from February to April. An area of active thunderstorms affected Hong Kong in the evening of April 8 and the Thunderstorm Warning and the Amber Rainstorm Warning were issued for the first time of the year.
May was slightly drier than usual while June was wetter than usual.
July was warmer and drier than usual. The monthly mean minimum temperature of 27.6 degrees equaled the record high value set in 1993. The monthly rainfall of 101.8 millimetres, less than one third of the normal figure of 323.5 millimetres, was the lowest on record. Waterspouts and funnel clouds occurred over Hong Kong waters on July 1, 6, 9 and 31. With the approach of Severe Tropical Storm Koni, the first Tropical Cyclone Warning Signal of the year was issued on July 20. The first Number 3 signal and later the first Number 8 Tropical Cyclone Warning Signal of the year were issued on July 23 as Typhoon Imbudo approached Hong Kong.
August was cloudier and wetter than usual. Typhoon Krovanh necessitated the issuance of the No. 3 Strong Wind Signal in Hong Kong. It was wetter than usual again in September. As Typhoon Dujuan skirted the north of Hong Kong about 30 kilometres from the Hong Kong Observatory on September 2, the Increasing Gale or Storm Signal No. 9 was issued for the first time since 1999.
October was sunnier and much drier than normal.
November was wetter than normal.
December had only a trace of rainfall recorded. The monthly rainfall ranked the second lowest together with seven other years since records began.