Monsoon season on Thailand's Andaman coast, month by month
Southwest and northeast monsoon dates from the Thai government, with rainfall and strong-wind days by month at Phuket (NASA data, our calculation).
SW monsoon
mid-May–mid-Oct
Land Development Department
Source: Land Development Department, Thailand, checked
Checked
29 Oct 2026
official dates, our calculation
On Thailand's Andaman coast (Phuket), the rainy southwest monsoon usually runs from mid-May to mid-October and the northeast monsoon from mid-October to mid-February, according to Thailand's Land Development Department; our NASA POWER calculation at Ao Chalong gives about 266–360 mm of rain a month from June to September against 52 mm in February. Charter prices are lower in the monsoon months (see best time to charter in Thailand for the price data); ask your base which anchorages stay sheltered in a south-westerly, and expect some days in port.
Checked 29 Oct 2026. Official dates are quoted; counts are our calculation from NOAA and NASA data (how we count); facts are labelled official, secondary or not verified (labels).
Southwest and northeast monsoon
- "The southwest monsoon usually starts in mid-May and ends in mid-October while the northeast monsoon normally starts in mid-October and ends in mid-February." (Land Development Department, Thailand; a Thai government department, not the Thai Meteorological Department) (Land Development Department, Thailand)
- During the southwest monsoon the department describes "abundant rain over the country, especially the windward side of the mountains"; the Inter Tropical Convergence Zone and tropical cyclones "produce a large amount of rainfall" in the same period. Our reading: Phuket and the Andaman coast are on the windward (west) side in the southwest monsoon (Land Development Department). (Land Development Department, Thailand)
- Of the northeast monsoon in the southern part of the country the department says it "causes mild weather and abundant rain along its east coast" (Land Development Department). (Land Development Department, Thailand)
Our calendar below marks May (from mid-May) to October (to mid-October) as southwest monsoon and October (from mid-October) to February (to mid-February) as northeast monsoon, our mapping of the department's words. When to go, with prices and the best months: best time to charter in Thailand. This page prints no prices and no best-month verdict.
Our best-time and family pages do not yet use these monsoon dates in their rules; they still name no best-weather months for Thailand.
Month by month
| Month | Monsoon (LDD) | Rain (mm, our calculation) | Mean wind (kn) | Force 5+ days | Force 6+ days |
|---|---|---|---|---|---|
| January | NE monsoon | 104 | 6.5 | 0.1 | 0.0 |
| February | NE monsoon (to mid-February) | 52 | 6.5 | 0.0 | 0.0 |
| March | – | 71 | 5.5 | 0.0 | 0.0 |
| April | – | 150 | 5.2 | 0.0 | 0.0 |
| May | SW monsoon (from mid-May) | 318 | 6.0 | 0.0 | 0.0 |
| June | SW monsoon | 266 | 7.2 | 0.2 | 0.0 |
| July | SW monsoon | 283 | 7.7 | 0.2 | 0.0 |
| August | SW monsoon | 326 | 8.1 | 0.1 | 0.0 |
| September | SW monsoon | 360 | 7.7 | 0.2 | 0.0 |
| October | SW → NE monsoon (to mid-October, from mid-October) | 345 | 6.2 | 0.0 | 0.0 |
| November | NE monsoon | 308 | 5.6 | 0.0 | 0.0 |
| December | NE monsoon | 214 | 6.5 | 0.0 | 0.0 |
Rain = NASA POWER's corrected precipitation for the grid cell at Ao Chalong, 2016–2025 (our calculation); it is not a Thai Meteorological Department rainfall normal. Force 5+ = 17 kn or more, force 6+ = 22 kn or more (Met Office lower limits). Our grid cell shows no force 6 days in any month; this does not mean calm seas, because the cell averages a large area and does not show squalls, gusts or sea state.
What the official sources say
- "The southwest monsoon usually starts in mid-May and ends in mid-October while the northeast monsoon normally starts in mid-October and ends in mid-February." (Land Development Department, Thailand; a Thai government department, not the Thai Meteorological Department) (Land Development Department, Thailand)
- During the southwest monsoon the department describes "abundant rain over the country, especially the windward side of the mountains"; the Inter Tropical Convergence Zone and tropical cyclones "produce a large amount of rainfall" in the same period. Our reading: Phuket and the Andaman coast are on the windward (west) side in the southwest monsoon (Land Development Department). (Land Development Department, Thailand)
- Of the northeast monsoon in the southern part of the country the department says it "causes mild weather and abundant rain along its east coast" (Land Development Department). (Land Development Department, Thailand)
If the weather turns
- Emergency: the page prints both "191 (ambulance, fire, police)" and separate numbers: ambulance 1669, fire 199, police 191, tourist police 1155. The two lines differ for ambulance and fire; we do not know which to prefer, according to UK government travel advice. (UK FCDO (GOV.UK))
- [Not verified] Sea-rescue number: we found no official page we could read, so we give no number.
- 7-day sailing itinerary in Thailand
- We opened no official forecast page for this area, so we link none.
Cancellation, insurance and weather guarantees
Booking in a risk season? Read your charter contract's weather and hurricane clauses: what happens if a named storm or a port closure stops you sailing, and whether you get a refund, a credit or new dates. Some booking platforms and charter companies sell cancellation options or a "weather guarantee", and some travel insurance covers trip cancellation or cutting a trip short because of weather; check what triggers the cover. We have no insurance partner and do not recommend a product. See our affiliate disclosure.
See boats in Thailand
See catamarans for rent in Thailand on SamBoat
Ask the operator about its weather and hurricane policy before you book; listings and prices on SamBoat are SamBoat's own. We may earn a commission if you book through our links, at no extra cost to you (disclosure).
How we count
Strong-wind days: from NASA POWER's daily WS10M_MAX (the highest hourly mean 10 m wind of the day in one grid cell), converted to knots (1 m/s = 3600/1852 kn), we count the days per month at or above 17 kn (Beaufort force 5, fresh breeze) and 22 kn (force 6, strong breeze), the lower limits on the Met Office scale, as a mean per month over 2016–2025. Direction shares use the day's mean wind direction (WD10M) in 45° bins. Our calculation.
Rain: NASA POWER's monthly corrected precipitation (PRECTOTCORR, mm/day) times the days in each month, averaged over 2016–2025, whole millimetres. Our calculation, not a rain-gauge normal.
Calendar: a month is marked if any part of it falls in the source's window (our mapping). "Mid-July", "the cold part of the year" and similar are the source's words.
Constants: strong-wind thresholds 17 kn (force 5) and 22 kn (force 6), years 2016–2025, 45° direction bins, NASA POWER API v2.10.1.
Weather data obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) Project, funded through the NASA Earth Science Division (pulled 29 Oct 2026) (NASA POWER, checked 29 Oct 2026). We changed the data: we counted days above thresholds, binned wind directions and summed daily rain into months (our calculation). Mean wind: NASA POWER monthly means, as on our other pages.
- Storm passes are historical frequencies for 1991–2020 within 100 nm of one reference point (our choice of radius); they are not a forecast, and a pass within 100 nm does not mean storm-force winds at the anchorage.
- Strong-wind days use NASA POWER's highest hourly mean wind of the day in a ½° × ⅝° grid cell (about 50 km across); real gusts and local winds (funnelling between islands, the bora at the foot of the mountains) are stronger than the cell shows.
- Some grid cells include land (elevation from NASA POWER: 11 m at Ao Chalong, Phuket), so their winds are lower than at sea.
- Wind direction is the cell's daily mean direction; north-easterly days are our proxy for the bora and northerly days for the meltemi, not observed events.
- Rainfall is NASA POWER's corrected precipitation for the cell, not a rain-gauge normal from the national weather service.
- Official dates ("mid-July", "the cold part of the year") are quoted; our month mapping in the calendar is ours.
Data: JSON.
What we could not verify
- The Thai Meteorological Department climate page (it returned HTTP 500 to us).
- Phuket station rainfall normals from the Thai Meteorological Department.
How to read the labels
- [Peer-reviewed study, not a government source]: a published scientific paper, used where we could open no official page; labelled secondary in our data.
- [Secondary source]: From a newspaper, NGO, guide or tour operator; not official.
- [Not verified]: We could not confirm it. We leave it open rather than guess.
- No label: Read in an official text: government, park authority, ministry or official tourism board.
Counts, shares, means and rainfall totals are our calculation, and say so; radii, thresholds and month mappings are our choices; "our reading" marks an interpretation. None of this is a forecast, a probability or a safety rating.
Sources
- Land Development Department, Thailand: General climatic condition (monsoons) (official), checked 29 Oct 2026.
- NASA POWER: Prediction Of Worldwide Energy Resources: Daily API (WS10M_MAX, WD10M) and Monthly API (PRECTOTCORR) (official), checked 29 Oct 2026.
- NASA POWER: Prediction Of Worldwide Energy Resources: Monthly API (T2M, WS10M) (official), checked 28 Oct 2026.
- Met Office: Beaufort wind force scale (official), checked 29 Oct 2026.
- UK FCDO (GOV.UK): Thailand travel advice: getting help (official), checked 29 Oct 2026.
Method: methodology. Data: JSON.
More
Frequently asked questions
When is monsoon season in Phuket?
Thailand's Land Development Department says "the southwest monsoon usually starts in mid-May and ends in mid-October while the northeast monsoon normally starts in mid-October and ends in mid-February" (Land Development Department, Thailand, checked 29 Oct 2026). Our reading: Phuket and the Andaman coast are on the windward (west) side in the southwest monsoon.
Can you charter a catamaran in Phuket in the rainy season?
We have no official source on whether charter bases operate or what sailing is like in the monsoon, so we do not say yes or no. The facts: the southwest monsoon runs mid-May to mid-October (Land Development Department), and our NASA POWER rain calculation is about 266–360 mm a month from June to September. Ask your base which anchorages stay sheltered and what it does on bad-weather days; prices are on best time to charter in Thailand.
Which is the wettest month in Phuket?
In our NASA POWER calculation (corrected precipitation, 2016–2025, one grid cell at Ao Chalong) September is the wettest month with about 360 mm and February the driest with about 52 mm. This is our calculation, not a Thai Meteorological Department normal, which we could not read.
When is the northeast monsoon?
The Land Development Department says the northeast monsoon normally starts in mid-October and ends in mid-February; in the southern part of the country it "causes mild weather and abundant rain along its east coast" (Land Development Department, Thailand, checked 29 Oct 2026).
Is the Gulf of Thailand different?
We only hold data for the Andaman (Phuket) point; the Land Development Department says the northeast monsoon brings rain to the south's east coast (its words: "mild weather and abundant rain along its east coast").