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 Track Probability Forecast Track Probability

Tropical Storm SON-TINH
at 17:00 HKT 18 July 2018

Position: 18.7 N, 107.2 E (about 830 km west-southwest of Hong Kong)
Maximum sustained wind near centre: 75 km/h

Son-Tinh will move across Beibu Wan and the northern part of Vietnam today and tomorrow.

Tropical Cyclone Track at 17:00 HKT 18 July 2018

Tropical Cyclone Track at 17:00 HKT 18 July 2018

Forecast Positions and Intensities

Date timePositionClassificationMaximum sustained wind near centre
17:00 HKT 19 July 201819.7 N103.4 ETropical Depression45 km/h
17:00 HKT 20 July 201820.9 N101.7 ELow Pressure Area25 km/h

( Past Positions and Intensities )


  • The symbol low pressure area symbol will be displayed when the tropical cyclone is expected to weaken into a low pressure area or transform into an extratropical low.
  • Past track is in black, forecast track is in red.
  • The tropical cyclone symbol in different colours are the forecast positions of the tropical cyclone at different times (as shown at the upper left corner of the figure).
  • While the forecast positions and track indicate the most likely future path of the tropical cyclone, they may deviate from the actual path taken by the storm. The yellow shaded area on the map indicates the probable area within which the tropical cyclone will fall with a probability of 70% ('Potential Track Area'). Literally, it means that in 10 times of track forecast for similar situations, the tropical cyclone will be centred within the indicated area in about 7 times. The area grows as the forecast hour increases. It will be particularly larger beyond 72 hours and is indicated with lighter shadings on the map. The size in terms of radius of the 'Potential Track Area' corresponding to different forecast hours are determined from the error statistics of the forecasts issued in past years and are as shown in the following table:

    Analysed Position30 km
    24-hour forecast position125 km
    48-hour forecast position225 km
    72-hour forecast position325 km
    96-hour forecast position400 km
    120-hour forecast position500 km

  • The tropical cyclone track, analysed positions and maximum sustained wind near centre are based on Hong Kong Observatory's tropical cyclone warning for shipping issued eight times a day at 0:30, 3:30, 6:30, 9:30, 12:30, 15:30, 18:30 and 21:30 HKT, about one and a half hours after the time of observation. The analysed positions incorporate additional information derived from surface and upper-air data and may therefore be slightly different from the real-time satellite or radar-based provisional positions given in the hourly bulletins for public. Meanwhile, the webpage will also display other information, including distance and bearing of the tropical cyclone relative to Hong Kong.
  • The past tropical cyclone track, analysed positions and maximum sustained wind near centre may be updated when additional data is received.
  • Short-term erratic departures of the tropical cyclone from the general direction of movement may occur from time to time. These departures are partly due to uncertainties in locating the centre of the tropical cyclone, and partly due to actual short-term variations in the direction and speed of movement of the tropical cyclone itself.
Last revision date: <18 Jul 2018>