The Weather of March 2018
4 April 2018
March 2018 was unseasonably warm and sunny with little rain. The total duration of bright sunshine of 196.2 hours in the month was more than twice the normal of 90.8 hours and was the highest on record for March. The monthly mean temperature was 20.8 degrees, 1.7 degrees higher than the normal of 19.1 degrees and one of the fourth highest on record for March. The total rainfall in the month was 22.7 millimetres, only about 28 percent of the normal of 82.2 millimetres. The accumulated rainfall of 89.4 millimetres since 1 January was about 45 percent below the normal of 161.3 millimetres for the same period.
Affected by a mild and humid maritime airstream over the coast of Guangdong, the weather in Hong Kong was warm and foggy with sunny periods in the early part of the month, with conditions turning cloudy on 3 – 4 March and visibility in the harbour falling below 1000 metres in fog. There were also a few showers and isolated thunderstorms on the morning of 4 March. After another foggy morning on 5 March, the weather turned fine and rather warm during the day.
A cold front moved across the coast of Guangdong on the night of 5 March. Windy conditions under the influence of a strong easterly airstream cleared away the lingering fog patches, and the weather in Hong Kong turned cloudy and appreciably cooler with light rain patches over the next couple of days. Rain associated with the passage of another cold front on the morning of 8 March made up most of the rainfall for the month, and under strengthening northerly winds, temperatures plummeted during the day with temperature at the Hong Kong Observatory reaching a minimum of 11.1 degrees, the lowest of the month, on the morning of 9 March. The cold air mass of continental origin also brought drier conditions and the weather turned sunny during the day.
A spell of fine weather with abundant sunshine then persisted till 13 March, with winds turning easterly and temperature gradually on the rise. With a humid maritime airstream pushing back towards the coast of Guangdong, the weather became cloudy with light rain patches on 14 March. The weather turned fine and warm over the next couple of days apart from some morning fog on 16 March.
A fresh to strong easterly airstream brought slightly cooler weather and light rain patches to the territory on 17 March. With the easterly winds moderating over the next couple of days, the weather in Hong Kong became warm with some mist patches early on 19 March. The passage of a cold front on the morning of 20 March brought cooler weather and a dry northeast monsoon to the coastal areas of Guangdong. Sunny weather prevailed in Hong Kong over the next three days, with daytime relative humidity falling below 40 percent on 21 March.
Winds gradually turned easterly and moister air of maritime origin brought cloudier skies on 24 March. A weak northeast monsoon then generally prevailed over the coast of Guangdong over the next few days and despite a replenishment of easterly winds towards the end of the month, the weather remained generally fine and warm in Hong Kong. With abundant sunshine, temperature at the Hong Kong Observatory climbed to the month’s highest of 27.9 degrees on 30 March.
One tropical cyclone occurred over the South China Sea and the western North Pacific 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 March are tabulated in Table 2.
Warnings and Signals issued in March 2018
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 6 / 3 | 0630 | 7 / 3 | 0745 |
| 8 / 3 | 1045 | 8 / 3 | 1610 |
| 17 / 3 | 0345 | 17 / 3 | 1510 |
| 21 / 3 | 0140 | 21 / 3 | 0740 |
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 4 / 3 | 0840 | 4 / 3 | 1140 |
| 19 / 3 | 1800 | 19 / 3 | 2000 |
| Colour | Beginning Time | Ending Time | ||
|---|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT | |
| Red | 9 / 3 | 0600 | 9 / 3 | 2310 |
| Yellow | 10 / 3 | 0730 | 10 / 3 | 2100 |
| Yellow | 11 / 3 | 0600 | 11 / 3 | 1900 |
| Yellow | 18 / 3 | 0600 | 18 / 3 | 1800 |
| Red | 21 / 3 | 0600 | 23 / 3 | 2145 |
| Yellow | 25 / 3 | 1030 | 25 / 3 | 2145 |
| Yellow | 30 / 3 | 0600 | 30 / 3 | 1845 |
| Red | 31 / 3 | 0600 | 31 / 3 | 1945 |
| Beginning Time | Ending Time | ||
|---|---|---|---|
| Day/Month | HKT | Day/Month | HKT |
| 8 / 3 | 0600 | 9 / 3 | 1100 |
| Meteorological Element | Figure of the Month | Departure from Normal* |
|---|---|---|
| Mean Daily Maximum Air Temperature | 24.4 degrees C | 3.0 degrees above normal |
| Mean Air Temperature | 20.8 degrees C | 1.7 degrees above normal |
| Mean Daily Minimum Air Temperature | 18.6 degrees C | 1.4 degrees above normal |
| Mean Dew Point Temperature | 16.2 degrees C | 0.5 degree above normal |
| Mean Relative Humidity | 76 % | 6 % below normal |
| Mean Cloud Amount | 56 % | 23 % below normal |
| Total Rainfall | 22.7 mm | 59.5 mm below normal |
| Number of hours of Reduced VisibilityΔ | 13 hours | 99.1 hours below normal§ |
| Total Bright Sunshine Duration | 196.2 hours | 105.4 hours above normal |
| Mean Daily Global Solar Radiation | 16.55 Megajoule / square metre | 6.59 Megajoule above normal |
| Total Evaporation | 96.2 mm | 25.7 mm above normal |
| Remarks : | All measurements were made at the Hong Kong Observatory except sunshine,
solar radiation and evaporation which were recorded at King's Park
Meteorological Station and visibility which was observed at the Hong
Kong International Airport. |
| Δ | The visibility readings at the Hong Kong International Airport are based on hourly observations by professional meteorological observers in 2004 and before, and average readings over the 10-minute period before the clock hour of the visibility meter near the middle of the south runway from 2005 onwards. The change of the data source in 2005 is an improvement of the visibility assessment using instrumented observations following the international trend.
|
* Departure from 1981 - 2010 climatological normal, except for number of hours of reduced visibility |
|
§ Departure from mean value between 1997 and 2017 |
|
| Remarks : | Extremely high: above 95th percentile Above normal: between 75th and 95th percentile Normal: between 25th and 75th percentile Below normal: between 5th and 25th percentile Extremely low: below 5th percentile Percentile and 5-day running average values are computed based on the data from 1981 to 2010 |
