The mean minimum and minimum temperatures were 32.7 degrees Celsius and 27.3 degrees respectively, 2.2 degrees and 1.2 degrees higher than their corresponding normal reading. The mean temperature was 27.3 degrees, 1.7 degrees above its normal level.
The HKO said all of the three figures were the second highest on the record for September.
Three days with daily maximum temperatures at the HKO equal to or higher than 35.0 degrees in the month, the highest number on record for September.
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The total duration of bright sunshine of 237.4 hours was about 36 percent higher than the normal 174.4 hours and the eighth highest on record for September.
The maximum temperature at the HKO soared to 35.9 degrees on September 13, the highest of the month and the highest maximum temperature for September on record.
The daily mean temperature at the HKO reached 31.7 degrees on September 13 and 14, the highest on record for September. The minimum temperature of 29.6 degrees on Sept 14 was the highest on record for September, according to the HKO.
The month was also drier than usual, with a monthly rainfall of only 171.2 millimeters, about 53 percent of the normal 321.4 mm.
The accumulated rainfall for the year up to September was 1,999. 0 mm, about 11 percent lower than the normal figure of 2,242. For the same period, the millimeters were 8 millimeters.
READ MORE: Temperatures in parts of Hong Kong top 37 degrees.
In September, eight tropical cyclones occurred over the South China Sea and the Western North Pacific, according to the HKO.