Coastal Hydrographics

Coastal hydrographics is influenced by various factors which cause dynamics of coastal processes. The major factors such as winds, waves, tides, and currents are varied by each area and cause a different magnitude of coastal change in Thailand.

  1. 1.    Waves are natural phenomenon which can be categorized by its generation as 1) wind-generated waves which are resulted from the wind blowing and 2) the waves which are caused by the Tsunami.
  2. 2.    Tides are generated by the rotation of the earth and the influence of Moon and Sun. Three main patterns in the tides are semi-diurnal, daily or diurnal, and mixed tides. Besides, the spring tides are called when the Earth, Moon, and Sun are in line, and the neap tides are called when the angle of the Moon, Earth, and Sun is close to ninety degrees.
  3. 3.    Currents are the movements of seawater which can be categorized as 1) surface current which generated by wind blowing and 2) deepwater currents which influenced by the density of sea water. Most deepwater currents are flowed with low speed and in the opposite direction to the surface current. Additionally, there are other types of currents which influenced by the tidal effects and coastal winds.
  4. 4.    Land and Sea breezes, a land breeze is produced and blown seaward from the land at nighttime when the land is rapidly cooler than the sea. When this happens, the warmer air over the water is risen and moved landward, while the cooler air over the land is also moved to the sea. On the other hand, a sea breeze is produced and blown landward from the sea at daytime when the sea is still cooler than the land causing the rise of warmer air over the land and the replacement of the cooler air from the sea.
  5. 5.    Monsoonal winds, there are two monsoons influencing to Thailand’s coast, that are, the Northeast Monsoon and Southwest Monsoon. The Gulf of Thailand is influenced by the Northeast Monsoon during mid-October to February causing heavy rains and strong winds in the South of Thailand, while the heavy rains and strong winds occurred in the upper and eastern Gulf of Thailand during May to October is resulted from the influence of the Southwest Monsoon.    However, the Gulf of Thailand is quite smooth during March to April. In the Andaman Sea during the mid of May to mid-October is faced with frequent rain and strong winds especially in the period from August to September. During mid-October to February is recognized as a tourism period in the Andaman Sea because the Northeast monsoon blown in this period does not affect to this areas.
  6. 6.    Tropical cyclones, Thailand is mainly influence by the tropical cyclones generated from the Gulf of Thailand. The tropical cyclones are often generated in the sea where the temperature is more than 26 degree Celsius with high humidity. The cyclones are moved by wind from the east to the west and from the lower to higher latitudes, then, circularly moved back to the east. Tropical cyclone is grouped by it maximum speeds as the followings.

1)      Tropical depression is the lowest intensity of tropical cyclones with the wind speed not exceeding 63 km/h or 33 kt.

2)      Tropical storm is developed with the wind speed ranged from 63-118 km/h or 34-64 kt.

3)      Typhoon is classified as a strongest tropical cyclones with the wind speed over 118 km/h (64 kt)



Figure 1 The common monsoons and tropical cyclones influence on Thailand’s coast