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Jump to: Weather • Water Temperature • Visibility • Tides & Currents • Salinity
The conditions in the Similans are usually close to perfect during high season, however, this is not always the case. Please check weather reports, tides and currents before planning a trip to ensure your safety and comfort.
The Similan diving season from November to April coincides with the North Eastern Monsoon weather system. Along the west coast of Thailand slight off shore winds should make for perfect weather conditions in the Andaman Sea.
The air is generally cooler during the first few months of the season resulting in lower humidity and therefore less chance of rain. In recent years, however, rain storms that mark the change of the Monsoon weather system in October have lingered on through November and sometimes continue as late as December. Rainfall in Thailand is usually accompanied by stronger winds that can increase the wave height in the Andaman Sea.
When planning a trip to the Similan Islands be sure to check the weather forecast and sea conditions in advance. It is not recommended to travel to the Similans in waves over 1m in height as the crossing will be uncomfortable and there is a high chance of sea sickness. Travelling by speedboat in rough conditions is extremely dangerous, many operators will put profit first and tell you it is safe to travel to the Islands.
If you have any questions concerning weather at the Similan Islands ask our experts.
The monsoons of southeast Asia determine the Andaman Sea’s climate and water salinity. Between November and April the average surface water temperature is 29-30°C, sometimes rising to 31-32°C in April. There is little or no change in temperature as you descend underwater. Even at 30 metres depth there is only 1°C or less difference to surface temperatures.
Most divers feel comfortable in a 3mm shorty wetsuit, some opting to dive in board shorts and a rash guard vest. If you regularly feel cold when diving, even in tropical waters, a long 3mm or 5mm wetsuit should provide adequate protection. The use of gloves is generally not recommended and often not allowed by many operators.
If you have any questions concerning water temperature at the Similan Islands ask our experts.
The visibility underwater in the Similan Islands averages a distance of between 20 to 30 metres. There is little change in lighting conditions as you descend to 30 metres in depth.
The visibility may drop slightly after several days of bad weather and rough sea conditions. Due to the long distance from shore, run off from the land after storms rarely affects the sea around the Similan Islands.
Occasionally the sea can take on a greenish tone where visibility drops to between 12 to 20 metres. There are also sometimes small thermoclines of cooler green water that pass over dive sites, generally not lasting more than a few minutes.
On a Similan liveaboard it is difficult to predict the exact visibility in advance and it may change at different locations during your trip. Visibility is rarely so poor that divers become separated from their groups.
If you have any questions concerning visibility at the Similan Islands ask our experts.
Tides in the Andaman Sea are semidiurnal, meaning the water rises twice a day. Generally the tides around the Similan Islands are not too strong and provide suitable conditions for students and inexperienced divers.
Around full and dark moon the currents can become much stronger. If you do not like diving in strong currents be sure to check the lunar calendar and our tide tables before planning your dive trip to the Similan Islands. Not all Similan dive sites are suitable for drift diving with the current, some require effort to fully explore the site.
The ocean currents at Koh Tachai and Richelieu Rock to the north of the nine Similan Islands can be much stronger and for this reason are classed as more advanced dive sites. Some dive operators recommend these sites for advanced open water divers only. Approach operators who boast that these sites are suitable for all levels of divers with caution.
If you have any questions concerning tides and currents at the Similan Islands ask our experts.
Water salinity is 30 – 33‰ per thousand (approximate grams of salt per kilogram of solution), slightly less than the average 35‰ salinity for the world’s seawater or compared with 40‰ for divers used to diving in the Red Sea.
As the Andaman Sea has lower salinity than many other oceans, you need fewer weights; many divers dive with excessive weight in the Similan Islands, which leads to buoyancy problems and poor air consumption. Dive staff generally have plenty of patience for divers wishing to perfect their weighting so don’t hesitate to experiment to get things right.
If you have any questions concerning water salinity at the Similan Islands ask our experts.
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