Andaman Sea Dive Sites: Weather Patterns
This short article is an explanation of the weather patterns and diving conditions throughout the year both in Phuket and the rest of Thailand. This information will be useful in helping to plan your diving holiday and will help you to weed through all the rumors and falsifications one hears about the weather in Southeast Asia. This is mostly to explain why we have a certain diving season and why Phuket liveaboards do not generally run from June until November.
Monsoon Means "Weather" (Not Rain!)
The term monsoon means "a weather pattern in Asia" (from Arabic mawsim, meaning "season"), and in Thailand, we have two monsoons during the year, the southwest and the northeast. Many people say we have three real seasons in Thailand; cool from November until January; hot from February until July; and rainy from August until November.
Northeast Monsoon, the Andaman High Season
The northeast monsoon lasts from October until May and is considered to be the high season in Phuket and most the rest of Thailand. This is generally understood to be the best time of year for both traveling and scuba diving. This is true to a certain extent, as the weather tends to be consistent and predictable during these months. The main reason it is the popular time, though, is that its winter in Europe and the US where most of our visitors come from; people are simply traveling to escape the cold and dark. Northern hemisphere winter is the most popular time for tropical holidays or vacations and is "high season" in almost every tropical area.
During this time in Thailand, since the wind is blowing from the northeast, on the West Coast of Thailand (the Phuket side), boats can reach even the most remote of sites as the winds dont really cause any large waves and there is no ground swell in the Andaman Sea. And, during the months of February, March, and April, the sea is generally flat and the sea looks and feels more like a lake than an ocean. The Andaman Sea is surrounded by land-mass (though far away) and is almost just a large lake! These months are when the Andaman Sea turns into a flat, glassy sea where more often than not you can look over the side of the boat and see your reflection in the water. The pattern is that it's breezy in the morning, and it dies down in the late morning. Thus, the morning may be choppy, but the afternoons are windless and smooth.
October to May: Very Predictable, Like Clockwork
During the beginning of northeast monsoon, around December, the wind can be 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. Because Phuket is on the other side of the Isthmus Kra, the land protects us from most wind and only certain dive sites are effected and difficult to get to at this time. This can be in December or January, usually not both.
This pattern is very consistent and very predictable, so the boat captains know what to expect and rarely do we need weather reports or weather satellite updates. It's pretty much how it is every day. We can plan our travel times according to the tides to avoid the chop, then get to a nice anchorage and enjoy ourselves.
Southwest Monsoon: Not So Predictable
The southwest monsoon, beginning in May causes waves & wind to come from the southwest and since Phuket faces the west, the waves are hitting the popular West Coast beaches directly making the Andaman Sea feel more like an ocean rather than our usual glassy lake. There are not too many nice beaches on Phuket's East Coast, so people have trouble finding nice swimming beaches during that time here. Phi Phi has nice swimming beaches–and so does Racha Island–all year around.
Rain is more common which makes the country-side more green, tropical, and beautiful. However, we can't accurately predict the weather more than a few days in advance and this makes it difficult to plan longer dive trips. And, since our dive sites are well offshore, the liveaboards generally only run when we can safely and accurately predict the weather. That means October until April. This is one reason when you search our schedules, you don't find trips to the Similan Islands or the Mergui Archipelago during the summer months.
The Gulf, since it is protected for the most part from westerly winds, experiences flatter seas than Phuket does during the southwest monsoon. However, it rains there just as much as it rains in Phuket during that time. The diving, for instance, in Koh Tao, gets very nice in June through September making it a great time to visit this lovely little island. The problem is that the diving doesn't compare to the Andaman Sea; never has, never will.
For those of you planning a hotel stay early or late in the season, keep in mind that Phuket is one of the driest provinces in Thailand and a lot dryer than Phang-nga province to the north of us or Krabi to the east of us. In other words, Phuket get less rain overall than these other places. This is one of the main reasons Phuket developed developed a tourism industry before other areas.
Not an Area of Large Storms
Compared to most other places in the world that are above or below 20º from the Equator, the weather here is not harsh. We rarely get typhoons or hurricanes or even tropical depressions. Besides the constant heat here, we have some of the best, safest and most predictable weather in the world. During the northwest monsoon, people rarely get seasick on boats.
Why We Dive When We Do
The trick for diving here is having protection from the waves. Unfortunately, many of Thailands dive sites do not have protection from rough weather as we are diving at pinnacles and other areas offshore away from large islands. Fortunately, we rarely have seriously rough seas and we can usually get back to protected areas quickly when necessary. Since the sea height is unpredictable during the southwest monsoon on the Phuket side, and unpredictable during the northeast monsoon on the Gulf side, it makes it difficult to plan trips to any areas that dont offer proper protection from the waves. Thus, trips to Sail Rock in the Gulf and trips to Richelieu Rock from Phuket are difficult since these dive sites have little protection from the weather. Due to the distances involved in making trips to Burma (Mergui trips are usually a 1,000km round trip), we generally do not schedule trips to these areas during the southwest monsoon (June until October).
Since the distances to the dive sites of better quality (Similan, Burma, etc.) are further away, we normally do trips there for several days. Therefore, to plan trips of any length of time (overnight or longer) we need to be reasonably sure that the diving will be good when we get there, and that there are safe and comfortable anchorages for the customers on board. Another consideration is getting divers on and off the boat safely and comfortably. If the waves are too large, then the dive platform can be a dangerous place if you're trying to re-board the boat.
Similan & Surin Islands All Year? Not Right Now
One of the islands which offers world class diving year-round, Koh Similan, is large enough that if there are waves, we can get shelter behind the island (on the East Coast). And, since the Similans are almost 40 nautical miles from shore, visibility is never effected by rain run off. In fact, during the southwest monsoon, since the water is moving up from the southwest, waves and currents are bringing in clear, clean water from offshore.
The main problem diving the Similan Islands during the summer months, June until September, is the lack of people wanting to go–not that we physically cannot. At that time of year, people are traveling to more temperate climes rather than the hot tropics, so historically there are very few scheduled liveaboards during this time as we 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 financially successful at it.
However, as of 2007, the Thai Government has officially closed Mu Koh Similan and Mu Koh Surin National Parks to tourism from May 15 until October 15 every year, giving them a much-needed rest from human activity. At this point, anyone going to the national park during the summer months is officially violating the law.
What about Mergui?
While it's legally possible to dive the Mergui Archipelago during the summer months, the distances involved are far to the best dive sites, and more importantly, the best dive sites are small rocks and submerged pinnacles which we can't reach during the southwest monsoon. So, most companies don't bother. Some dive companies take their boats to Indonesia during this time. We're happy to help you find a trip there too.
Day trips: Dive Phuket, Phi Phi, Samui and Koh Tao All Year-Round
Since day diving destinations do not have long travel times, nor do they have to be planned in advance, almost all dive centers in Thailand offer fine diving at all the popular spots around Phuket and Phi Phi Island in the Andaman Sea, and Koh Tao, Samui and Pattaya in the Gulf of Thailand (Siam). Off season is a great time to visit Thailand as prices are down, there is less traffic and people on the roads, and more options for general tours and hotels since there are fewer (if any) package tourists here. Visibility is generally not very much different between high season and low season as visibility is effected more by plankton and algae blooms rather than freshwater run off. If we've had heavy rain or a long storm, visibility drops, but after a few days it's right back at good again. So, if you're here during our "Green Season" you can dive, but a liveaboard will more than likely not be possible.
John and Bent
[Note: Tsunamis are extremely rare and caused by earthquakes and are not a weather condition. Yet, we had one on December 26, 2004 that caused a huge loss of life especially on the coast north of Phuket around Khao Lak and in Phi Phi Island. No on expects this to happen again in any of our lifetimes. Phuket fully recovered from the effects of the waves in a few weeks. Khao Lak and Phi Phi have recovered completely as well (though it took longer there as most hotels had to be rebuilt) and all destinations on the West Coast are busier than it's ever been. Diving conditions are normal and pretty much the same as prior to the tsunami as our activities take place in deeper water where the waves just passed over (no one died underwater in the tsunami as far as we know). Some of the coral reefs which lie in shallow water which were exposed to heavy surf and strong currents suffered damage, but divers do not generally see this as we don't dive in these areas.]
About the Author
John Williams has written, co-authored, or contributed to four diving guides on Thailand, the Mergui Archipelago, and the Andaman Islands. These are the award-winning Lonely Planet Diving & Snorkeling series, Periplus Editions Diving Southeast Asia, Asian Diver Scuba Guides and Singapore's Times Edition Diving Thailand. He has lived in Phuket and dived in Thailand's waters since 1987.