Wet season information

My wet season post is close to dropping off the end of the branch, so I will repost it here and use this as a URL for future questions.

<hr>
Questions about the wet season in Thailand come up so often that they often go unanswered. So I have put together this summary which I’ll cut and paste into similar posts. I don’t claim to be an expert, but I’ve been reading posts, asking fellow travellers on the road and seeking statistics for some time. I hope what follows may help answer your question.

<hr>
Most answers to questions on the wet season I’ve seen say things like:
You only get one or a few showers most days, with heaps of sunshine in between.
Or - No worries, we got great weather with only a couple of storms.
I always reckon you have to be cautious with reports from people who have spent only a few weeks or so in an area. Maybe it was an unusually dry year. Maybe it was a normal year and they were lucky. Maybe people with negative experiences think they were unlucky and keep quiet, not wanting to spoil things for other travellers.

I figure the most reliable information would come from someone who has experienced lots of wet seasons in full. So last trip I asked a European guy who has been running a bungalow operation for many years on the Andaman Coast what the wet season was like.
He actually shuts down his place from late May to late Oct, so has no advantage in making things sound good.
He said that at the extremes you can get 2 weeks of beautiful sunshine with no rain, or up to 2 or 3 days of continuous rain where the winds can be so squally and the seas so rough that ferries and longtails don’t run, swimming is dangerous and heaps of rubbish gets blown onto the beaches.
He said that more often you get days with one or two showers or storms, often with sunshine between.
This suggests the posters are pretty correct in that normally is not a real problem. However you may get unlucky and strike one of those less common prolonged wet spells.
Really this does not seem too much different from January in my part of Australia.
January is the most popular beach holiday month there.

Some statistics may help.

THE ANDAMAN COAST
I pinched this first bit from [url]sawadee.com[/url]
It gives some idea of the duration and rainfall amounts for the Andaman coast wet seaon.
For you Americans 25mm equals 1inch of rain (25.4 if you are a pedant).

Phuket / Krabi / Koh Phi Phi / Koh Lanta
Weather in Krabi is typically that of the tropical monsoon, providing the province with just two seasons, the hot season from January to April, and the rainy season from May to December. Monsoon winds, which change according to season, blow from the southeast, the southwest, and the northeast. Temperatures range between 16.9 and 37.3 degrees Celsius and the yearly rainfall averages 2,568.5 millimeters.
Best time for visit
December - April
Rain season
May - November

Krabi
Av Rainfall mm JAN35.0 F30.7 M38.8 A163.2 M348.2 J212.8 J263.0 A262.6 S419.3 O305.4 N207.3 D52.0
Year 2568

<hr>
Thanks sawadee
Figures for Phuket are similarJAN25 F25 M70 A125 M290 J280 J260 A270 S320 O340 N200 D60
Year 2265

THE SOUTHERN GULF COAST ISLANDS
The good news here is if you want to avoid the Andaman wet season, for most of the time it is appreciably drier across on Samui and its neighbours.
The really wet period for these islands in a normal year is Oct through Dec.

Here are the statistics for Samui
J100 F25 M50 A100 M150 J75 J125 A100 S100 O250 N425(!) D250
Year 1750

As you can see, the SW monsoon dries out a heck of a lot as it crosses the peninsula.
From 2 visits to Samui and neighbours in July-August and reading of many posts about weather here I can confidently say that in a normal year you would be dead unlucky to have your holiday in this area wrecked by rain between January and October. My mid year visits saw heaps of sunshine with a short storm, usually mid to late afternoon about 1 day in 3.
I have to stress the term normal year. In my ignorance, my first trip to these islands was in November which is supposed to be really wet. And yet I got beautiful weather - only 3 showers, each less than an hour, in 20 days. Look at the statistics - that’s not normal. I was lucky.
Another time At Khao Sok in February I listened to a girl newly arrived from Phangan complaining of 3 days continuous rain there. That’s not normal. She was unlucky.
But that’s weather for you.

BANGKOK and THE EASTERN GULF COAST
The pattern here seems much the same as the Andaman Coast except rainfall amounts are normally not quite as high and the wet season maybe a bit shorter.

Bangkok
J10 F20 M30 A60 M200 J160 J160 A170 S300 O210 N70 D5
Year 1235

I haven’t managed to find any statistics for KO CHANG or the nearest big town, Trat.
The best I could do is Chanthaburi which is about halfway between Chang and KoSamet. It is inland a small distance which may have some impact, maybe a bit drier than the coast.

Chanthaburi
mm J17.5 F37.0 M62.9 A117.4 M328.8 J499.6 J473.0 A476.4 S485.8 O259.8 N66.1 D13.4
Year 2855.4

There are no figures for KO SAMET, which is a pity because many posts and (from memory) LP say it is less affected by the monsoon than most coastal islands. Pattaya is the closest place I could get figures for.

Pattaya
mm J11 F23 M41 A79 M164 J119 J166 A166 S302 O230 N66 D10
Year 1377

Pattaya is certainly less rainy than Chanthaburi, and a hell of a lot drier than the Andaman places, so there may something in the reports about nearby Samet’s benign wetseason. Another good point may be that all but one of Samet’s tourist beaches face east and so would be sheltered from the prevailing SW monsoon winds - less rough water and less rubbish being blown onshore. Khunjimbo has some additional Samet info at the end.

THE NORTH
The general rule is that as you head inland it gets drier.
Chiang Mai
mm J7.5 F6.0 M15.0 A44.9 M153.1 J135.8 J167.1 A227.0 S251.3 O132.0 N43.9 D14.8
Year 1197.1
That’s not to say that you can’t be unlucky. Usually at least once a year I read reports of deluges, flooding and landslides somewhere up north.

Finally, in the EVERY CLOUD HAS A SILVER LINING department, I’ll include this answer from mr_potato_head on a query about the wet season:

5. Rainy season =
Fewer tourists
Cheaper prices
Hotel rooms widely available
No need to book ahead for trains/planes/buses
Reduced risk of melanoma
Beautiful cloud formations for your landscape/sunset photos
Cooler weather

<hr>
And for another finally, here is a very recent comment on my stuff from jinxx which may be helpful:
I think the Andaman owner was overstating things a little. I only ever go to Southern Thailand in the off season because prices are 60%, there is no problem getting a booking and in, the south, say in 10 trips, I have never been inconvenienced by rain by more than say 2 hours.

For places only accessible by boat the story changes - you can get stuck.

In Bangkok the annual average is >1200 mm. In aggregate time though this would amount to around to maybe 200-350 hours/year.

My advice: Buy your ticket but pack in a fold-up umbrella.

<hr>
And yet there’s more!
Kunjimbo, who lives at Ban Phe, the port for Ko Samet, contributed the following:
Ban Phe/Samet areas are supposedly the driest in Thailand. The rainy season here is June to October, although we've had some rain recently, and I've also seen rain in November. When it rains, it really comes down. Some crashing-good thunder&lightning storms too. It usually does that at night or early morning. I only remember a couple of days in the 2 years I've lived here when it rained all day. Like other posters have pointed out on other threads, Thai rainstorms are intermittent and are no reason to cancel or postpone trips. Samet is more protected, up here in the far north-middle of the gulf. When it does rain, sometimes the water gets too choppy for speedboats, and that makes the slow ferry trip to/from the island tough for those who get seasick. The flipside of being in a dry region is that it gets really hot & dusty in Ban Phe, with not enough rain to tamp it all down. But hey, that's not a big problem on Samet -- just jump in the sea!