Ko Lanta Yai and Ko Lanta Noi are islands of Lanta archipelago, in S Thaïland, in the Andaman sea.
They are separated from the S side of Ko Klang by a narrow shallow channel.

From seaward these islands appear as one.

The N part of Ko Lanta Yai is mostly flat and low-lying with several isolated hills. The S part consists of a narrow ridge of steep hills which attain an elevation of 491m.

Ko Lanta Yai is a long thin island running north through south, 6 kilometers wide and 40 kilometers long. The west coast (or sunset coast) faces the Andaman Sea with a string of beautiful white-sand beaches that hosts the island’s resorts.
The National Park office is located at the southern end of the island, and is a fantastic area for bird watching and nature trekking.

The Ko Lanta archipelago covers an area of over 180square kilometers and includes a total of 52 islands. It was declared as Thailand’s National Park No.62 in 1990, in an offer to protect the fragile coastal environment.

The archipelago consists of for small group of islands, mainly known as the Ko Ngai (Hai) group, the Ko Rok group, the Ko Ha group, and the Ko Lanta group.

80% of the archipelago is in the sea, and is protected under the Marine Park authority, ensuring underwater lives and the reefs within remain fresh and unspoiled. Diving and snorkeling within the area offers characteristics unique to these sites alone. 

Tides/Curents:

In the channel E of Ko Lanta Yai, the tidal currents set N and S at a rate of 1 knot to 1.5 knots.

Weather and Climate:

Weather on Ko Lanta is typically that of a tropical monsoonclimate. The monsoons change direction twice a year. Coming  once from the south-west and once from the north-east. This causes Ko Lanta to have only 2 seasons-  summer season and rainy season. The tourist season in Ko Lanta runs from October through until May with most visitors arriving from November to March.

The South-West monsoons brings  rain to the island during low season. Ko Lanta’s mountain range blocks some rain and aids jungle regrowth on the west side, as well as filling up the reservoirs.