Similan Islands Weather

The Similan Islands Weather renders the park  closed from May 15th to November 1st of each year. It is illegal to visit during this time – but it’s also a bad idea! The weather can be rough or it can be smooth and it can change without notice. It’s a chaotic time and we strongly discourage any attempts to visit during this time.

Similan Islands Weather Information

Honeymoon Bay from the SouthThe monsoons play an important role in all apsects of life on the Similans. The monsoons always head in from the South West over the Andaman Sea. So The east coast is protected from the monsoons features powdery coral beaches, coral gardens of hard and soft corals which slope dramatically from the surface down to approximately 30-40 meters. Whereas the West coast is generally made up of the large boulders dropping intot he depths. The flora is very much affected by the constant winds and have very daramtic scenery with no beaches (The protected Donald Duck bay is the exception)

Thailand has three seasons; a bit cool, hot and rainy. The best time to visit (for consistently great weather if you love the sun) is between October and May. The summer months of July and August are customarily very pleasant, although it tends to rain in the evenings. September is not usually the best time on the islands, as the seas are usually too rough for swimming (or diving) and rain fall is widespread.

With regard to water clarity on the Similan Islands, the water is actually more clear during the summer months; the islands are too far offshore to be effected by freshwater run-off

When is the best time to visit the Similan Islands?

While the park is open from November 1st through May 15th, the most popular time to visit is in December and Early January. However the least amount of rain, and the smoothest water is in Late February through Mid March. Temperatures start to rise, but the seas are very calm and the evenings are nearly perfect! There is always the chance of a bit of rain, and you will certainly need your sunscreen…but this is certainly the best time to visit the Similan Islands!

Diving and snorkeling is usually equally nice in the summer months, but it may be a good idea to carry some rain gear like a poncho for transportation between the boat and the car! It’s also very difficult to make it to the Similan Islands due to winds and waves. There are no day trips running. Be very WARY of companies that offer Day trips during these months. One shop in Khao Lak (Thai owned and operated) has sunk their Speedboat operating in the monsoons.

The Similan Islands weather in December 

Monsoons are the major factor in the weather conditions. When they are gone, the Similans are open! Even the occasional thunderstorm presents more opportunity than harm – we just consider it air-conditioning.

There are seasonal variations in currents – as the prevailing winds that bring the monsoons also bring in colder waters from the open ocean we tend to have even clearer water. Tidal currents are strong at the narrow points in the islands and at the Northern and Southern Tips.

While conditions in Khao Lak (and to a lesser extent) are sometimes cloudy or rainy, the Similan Islands get less than 1/2 the rainfall that the mainland get.

Summer begins in mid February and ends in May. Rainy season starts from mid May till October with North – Western wind. Average annual temperature is 27๐c with average of approximately 83% humidity all year round. Average annual rainfall is measured at 3,560 millimeters with evaporation rate of 1,708 millimeters per year. This means 2 meters of rain a year on average.

Similan Island Information: Monsoons

The northeast monsoon lasts from October until May and is considered to be the high season on the Similan Islands and in Khao Lak and is generally understood to be the best time of year for both traveling to and enjoying the Similan Islands. This is true to a certain extent, as the weather is consistent and predictable. The main reason it is the popular time, though, is that it’s winter in Europe and the States where most of our visitors come from, and people are escaping the cold.

During this time, since the wind is blowing from the northeast, on the West Coast of Thailand, boats can reach even the most remote of sites as strong winds don’t affect the sea until you reach far, far offshore. And, during the months of February, March, and April, the sea is generally flat and feels more like a lake than an ocean or sea. This is the transition time and it gets hot – 35 is not unheard of. The three months in the spring are hot here and the very best time for visiting the islands.

During the northeast monsoon, the wind can be very strong at times, 15-25 knots, so the Gulf of Thailand experiences fairly high waves and often times boats to Koh Samui or Koh Tao can not run due to the height of the waves. While that rarely affects the West Coast (Similans) it can cause some wind and even waves. Most reputable operators will advise guests of the risks (if any).

The southwest monsoon means the waves & wind now come from the southwest and since Khao Lak and the Similans face the west, the waves are hitting the West Coast beaches directly making the Andaman Sea feel more like an ocean rather than the glassy lake it usually is. Rain is more common which makes the country-side more green, tropical, and beautiful.

The Gulf, since it is protected for the most part from westerly winds, experiences flatter seas than Andaman Coast does during the southwest monsoon. However, it rains there just as much as it rains on the West Coast during that time.

The weather here is not severe. There are rarely typhoons or hurricanes or even severe tropical storms. Besides the constant heat here (and that’s not really a problem on the boats, islands or coastline) Khao Lak and the Similan Islands have some of the best and safest weather in the world.

The trick for visiting during these times is having protection from the waves. Unfortunately, many of the popular sites in the region do not have protection from rough weather. Since the sea height is unpredictable during the southwest monsoon on the Similan side, and unpredictable during the northeast monsoon on the Gulf side, it makes it difficult to plan trips to any areas that don’t offer proper protection from the waves. Thus trips toRichelieu Rock from Khao Lak are difficult since this site has little protection from the weather. Due to the distances involved in making trips to Burma (a 1,000km round trip), no one generally schedules trips to these areas during the southwest monsoon.

The main problem visiting the Similan Islands during the summer months, June until September, is the lack of people wanting to go–not that you physically cannot. At that time of year, people are traveling to more temperate climes rather than the hot tropics, so there are very few scheduled liveaboards during this time as boats can’t get enough people together on a consistent basis. Almost every boat at one time or another has tried a summer schedule and few, if any, have ever been successful at it.

A couple of great links to help you see the current conditions….

Read more about the wave and wind Forecast for the Similans

And the Thailand Meteorlogical Department also issues advisories and forecasts. Please bear in mind that these forecasts are for the mainland, and not the islands which often have a  very different weather pattern.