Eastern Thailand
Eastern Thailand Geography & Climate
Geography
Eastern Thailand runs from the eastern edge of the Bangkok plain to the Cambodian border, a strip of coast and hinterland between the Gulf of Thailand and the hills.
The coast
Around 500 kilometres of shoreline, low and sandy in the west around Chonburi and Rayong, becoming steeper and more indented toward Trat. The Gulf here is shallow and warm, and the water is noticeably less clear than on the Andaman side.
The islands
The Ko Chang archipelago near the Cambodian border holds more than fifty islands, of which Ko Chang itself is the second largest in Thailand at about 217 square kilometres. Unlike the limestone islands of the south, these are granite and volcanic in origin — steep, rounded, and covered in rainforest to the waterline, with the interior of Ko Chang rising above 740 metres.
The hills
Inland the ground rises into the Cardamom and Chanthaburi ranges, the western end of a forest belt that continues into Cambodia. This is some of the wettest country in Thailand and holds significant remaining forest, waterfalls and the gem-bearing gravels that made Chanthaburi.
Orchard country
The volcanic and alluvial soils around Chanthaburi and Rayong are unusually fertile and support the country’s densest concentration of tropical fruit orchards.
A different kind of island
The contrast with the south is worth stating plainly. Southern Thailand’s islands are limestone, with sheer walls, caves and the brilliant shallow water that photographs so well. The eastern islands are granite and volcanic — older, rounder, steeper and forested from ridge to shoreline — so they look more like a piece of mainland that has come adrift than like a rock rising out of the sea.
The industrial coast
Laem Chabang, Map Ta Phut and the Sattahip naval base occupy much of the western shoreline, and the deep-water port there is the country’s largest.
Climate Patterns
Eastern Thailand has a tropical monsoon climate, and it is one of the wettest parts of the country — the Cardamom foothills catch the south-west monsoon square on, and Trat province records some of the highest rainfall totals in Thailand.
The dry season
November to April brings highs around 31 to 34°C, lower humidity, calm seas and little rain. December and January are the most comfortable months, with overnight lows around 22°C.
The hot season
March to May is the hottest stretch, reaching 35°C or more with high humidity, though the sea breeze makes the coast more bearable than Bangkok.
The wet season
May to October is heavy. Annual rainfall on the coast and islands commonly exceeds 3,000 millimetres, considerably more than Bangkok, and it falls in sustained spells rather than only in brief afternoon storms. Seas are rough, and this is why more island businesses close here than on the Gulf islands further south.
The practical consequence
Ko Chang, Ko Kut and Ko Mak have a genuinely short season. Many resorts, dive operators and ferry services run only from about November to April or May, and turning up in August can mean a half-shut island and a rough crossing to reach it. Check what is actually open before booking low-season travel here.
Why it rains so hard here
The Cardamom range sits directly in the path of the south-west monsoon as it comes off the Gulf, and the moist air is forced up over it. The result is that Trat province and the seaward slopes of the hills record among the highest rainfall totals in the country — well above Bangkok, and comparable to the wettest parts of the Andaman coast — concentrated into five or six months.
Fruit and rain
The heavy rainfall is exactly what makes the orchard country productive, and the fruit harvest follows the first rains from April into June.