How High Do Waves Have to Be Before Ferries Stop Running? Understanding Thai Weather and Marine Warnings
A heavy rain warning covering dozens of provinces does not automatically mean ferries to Thailand’s islands will stop running. At the same time, a ferry can still be delayed or cancelled even when the sky is clear and the sea looks calm from the pier.
That is because ferry operations depend on much more than whether it is raining.
The important factors include wave height, wind speed, thunderstorms, the route the vessel must travel, and the size and capability of the vessel itself. If you are travelling to an island during the monsoon season, understanding Thailand’s marine weather warnings is much more useful than simply checking the chance of rain on your phone.
Which Thai Weather Warnings Matter for Ferry Travel?
There are two main types of warnings travellers should understand. Heavy Rain Warnings
These warnings mainly focus on risks on land, such as:
flash floods
landslides
flooding
disruption to roads and ground transportation
They can still affect island travellers because heavy rain may delay your journey from an airport, town or hotel to the ferry pier. However, heavy rain does not automatically mean ferry services will stop. Passenger ferries can operate in rain if waves, wind and visibility remain within safe limits. Strong Wind and Wave Warnings These are much more important if you are trying to find out whether your ferry will operate.
The Thai Meteorological Department usually separates marine forecasts by area, such as:
the upper Gulf of Thailand
the lower Gulf of Thailand
the upper Andaman Sea
the lower Andaman Sea
Warnings may state expected wave heights and often note that waves can become higher in areas with thunderstorms. If the forecast includes the phrase: “small boats should remain ashore” you should treat it as an important warning and check your ferry status directly with the operator.
How High Do Waves Have to Be Before Ferries Stop Running?
There is no single wave height that applies to every vessel. Thailand’s Marine Department uses guidance that considers wave height, wind speed and vessel length together.
A simplified version looks like this:
Approximate sea conditionsVessels that should not operateWaves Wind speed is also considered. For example, guidance associates waves of around 2 metres with winds of approximately 17–21 knots, while waves of around 3 metres may correspond with winds of around 22–27 knots.
However, this table does not mean every passenger ferry automatically stops at a certain wave height.
Other factors still matter, including:
vessel size and design
the vessel’s seaworthiness
the route
wind and wave direction
actual sea conditions
local Marine Department restrictions or orders
So the question: “Can ferries operate in 2-metre waves?”
cannot be answered from wave height alone. A small vessel may no longer be suitable to operate, while a larger passenger vessel may still be able to sail if the overall conditions remain within safe limits.
Does “Small Boats Should Remain Ashore” Mean All Ferries Stop?
No. This is a marine safety warning and does not automatically mean every ferry or passenger vessel must stop operating. The term “small boat” should not be interpreted only by vessel type, such as speedboat, long-tail boat or ferry. What matters is the size and capability of the individual vessel relative to the sea conditions. This is why, on some days, smaller speedboats may stop operating while larger passenger vessels continue running. However, if the Marine Department or a regional Marine Office issues a specific restriction or suspension for an area, that order should take priority.
Who Decides Whether a Ferry Can Operate?
Several parties are involved. Thai Meteorological Department The Thai Meteorological Department provides forecasts and warnings for: rain, wind, waves, storms and marine weather conditions These forecasts are an important source of information for ferry operators and marine authorities. Marine Department and Regional Marine Offices
The Marine Department can issue safety notices, restrictions or operational orders for vessels in specific areas.
If a local notice is issued, check carefully:
which area it covers
the period of the restriction
which vessels are affected
Ferry Companies and Vessel Masters
Even when there is no general prohibition on sailing, ferry operators or vessel masters can still delay or cancel a service if they believe conditions are unsuitable for that vessel. This means that seeing tickets still available online does not guarantee that the ferry will definitely operate. Sea conditions can change right up until departure time.
Why Is the Sea Calm at the Pier When the Ferry Is Cancelled?
Because conditions at the pier may be very different from conditions offshore. Many ferry piers are located inside bays or areas protected by islands, headlands or the coastline. The water may therefore look calm while the vessel is still at the pier. Once it leaves the sheltered area and enters open water, wave conditions can become much rougher. Another important point is that marine forecasts usually report significant wave height. This does not mean every wave will be exactly that height. Waves around thunderstorms can also be higher than the general forecast. So you should never judge the entire route based only on what the sea looks like from the pier.
Open Sea Routes Are More Sensitive to Rough Conditions
In general, routes that cross longer stretches of open water are more exposed to wind and waves than short crossings or routes protected by islands and coastlines. Routes serving destinations such as: Koh Tao, Koh Phi Phi, Koh Lanta and Koh Lipe can therefore be affected differently depending on the season and the exact route. The Gulf of Thailand and the Andaman Sea also experience their strongest monsoon conditions at different times of the year. Before travelling, check the forecast for the sea area your ferry will actually cross, not only the weather at your destination island.
What Should You Check Before Leaving Your Hotel?
If you have a ferry ticket during monsoon season, check at least these four things.
1. Check Wave Forecasts, Not Just Rain Forecasts
Pay attention to expected wave height and marine warnings for your route.
2. Look for “Small Boats Should Remain Ashore”
If this phrase appears in the forecast, confirm the latest ferry status before travelling to the pier.
3. Check Announcements From the Ferry Operator
Operators may announce:
delays
cancellations
schedule changes
combined departures
On days when weather conditions change quickly, check again on the morning of travel.
4. Check Local Marine Department Notices
If there is a local restriction or suspension on vessel operations, it is more important than the normal ferry timetable.
What Should You Do If Your Ferry Is Cancelled?
The first rule is: Do not try to find an unofficial boat to travel anyway. If services have been stopped because sea conditions are unsafe, switching to a smaller private boat does not make the sea safer.
Instead:
contact the ferry operator or ticket seller
ask about the next available departure
ask whether another permitted vessel type is still operating
check the refund or date-change policy
inform your hotel, transfer provider or tour company
Refund and rescheduling policies vary between operators, so it is worth checking them before booking, especially during monsoon season.
Avoid Booking a Ferry Too Close to Your Flight
This is particularly important when travelling during periods of unstable weather. Even when the weather looks good, ferry departures can still be delayed because of wind, waves or other operational issues. Leaving extra time before a flight significantly reduces the risk of missing it. For important flights, especially international departures, staying on the mainland the night before is usually the safer plan.
Frequently Asked Questions
Does a Heavy Rain Warning Mean Ferries Will Stop?
No. Heavy rain warnings mainly relate to rainfall and impacts on land. Whether a ferry operates depends on wave conditions, wind, thunderstorms, vessel type and marine safety notices.
Can Ferries Operate in 2-Metre Waves?
Possibly. Marine Department guidance indicates that vessels under 6 metres long should not operate when waves are around 2 metres. Larger vessels must still be assessed based on their design, capability, route and the actual conditions at the time.
Can a Ferry Still Operate in 3-Metre Waves?
Wave height alone is not enough to answer this. Guidance indicates that vessels under 9 metres long should not operate when waves are around 3 metres. But this does not automatically mean every vessel longer than 9 metres is safe to operate. The final decision still depends on the vessel, route, wind and local restrictions.
Why Is the Water Calm at the Pier but the Ferry Is Cancelled?
The pier may be located in a sheltered bay while the route passes through much rougher open water. The vessel must be able to travel safely along the entire route, not just leave the pier safely.
If the Morning Ferry Is Cancelled, Will the Afternoon Ferry Run?
Either is possible. Conditions may improve and later services may resume, or the operator may cancel several departures or the entire day. Wait for confirmation from the operator rather than assuming the next service will run.
Is It Risky to Book Ferry Tickets in Advance During Monsoon Season?
Booking early does not make the weather more or less risky. What matters is whether the ticket allows you to change the date, change the departure or receive a refund if the service is cancelled.
Gulf of Thailand ferry routes
Andaman Sea ferry routes
