The Basics of Marine Meteorology – A Guide for Seafarers

by | Last updated May 9, 2024 | Navigation, Shipboard Operations | 0 comments

Marine meteorology is a branch of science that studies weather and climate as they apply to the ocean and the coasts. Studying the phenomenon happening at sea is very important.

For one, the ocean comprises a huge part of our work environment. 70% of the earth’s surface is covered with water.

Seafaring out to sea gave me exposure to the complexities of the weather including the interaction between the sea and the sky.

It made me realize that correct observations of meteorological conditions will enable us to predict the weather. It doesn’t matter which type of merchant vessel you sail. Observing the weather at sea will always be of prime importance.

I remember an ancient proverb that goes,

“Red sky at night, sailors’ delight. Red sky in the morning, sailors’ warning.”

I often use them at sea and even on land because they are quite accurate! So if you want to know a little bit about the future, learn meteorology. Specifically marine meteorology.

What is Marine Meteorology?

Meteorology refers to the study of the Earth’s atmosphere. Since everything on earth is covered by the sky, the science of marine meteorology has its specific course.

Marine meteorology is also the study of the earth’s atmospheric conditions but with a direct relation to the ocean. It is the interactivity between the ocean environment and the atmosphere that sets it apart from other sub-fields of meteorology.

I highly encourage seafarers, especially those who want to become officers, to be a student of this course.

Rainbow forming over the horizon on the port bow of a tanker vessel.
Rainbow forming over the horizon.

How is Marine Meteorology Useful to Seafarers?

“Nihil sub sole novum”.

This is one of my well-respected quotes. It translates to,

“There is nothing new under the sun.”

Is there something new under the sun? Or is everything just a pattern occurring again and again and again like a cycle?

That quote above is taken from Ecclesiastes 3:11 of the Bible.

And I believe it is true with marine meteorology.

An accurate prediction of the weather helps seafarers avoid heavy seas or take appropriate actions to survive heavy storms.

Forerunners of a Storm

You see, before a storm happens, there are always forerunners that we can observe. Storm doesn’t just come the next hour and pour down on us.

There are noticeable changes in the elements around us before it arrives. We also use instruments like the wind vane, anemometer, and the ship’s barometer to predict the weather. These observations are much more pronounced at sea.

The good thing is, these patterns are repeating again and again and again for millennia!

And we can take advantage of that as the great galleon sailors of old-time did. Their expertise in marine meteorology enables them to sail around the world.

“Nihil sub sole novum”.

Basics of Marine Meteorology

Understanding marine meteorology involves careful observation of the weather, climate, and the forces acting between them.

Such forces are the pressure and temperature with the contribution of the sun’s energy, the wind, and the earth’s motion.

They all interact together in a layer of gasses surrounding our planet called the atmosphere.

A person using his phone near the ship's porthole showing the rainy environment outside.
Weather greatly affects our lives at sea. There are jobs on board that we need to do no matter as much as the weather permits.


In a simple sense, the weather is the condition of the Earth’s atmosphere over a brief period, at any given time.

It is a mixture of elements acting together to produce the current state of the sky. We always observe, measure, and log these elements on board to track the changes and predict the atmospheric condition.

When it comes to our day-to-day operation, weather is very critical. It directly affects how we navigate. Since it changes quickly, sunny waters could turn into poor visibility. Imagine having this scenario in tight pilotage areas!


A long-term meteorological condition over a certain region is called climate. Since weather can change in a blip- hour to hour, day to day, etc., a climate is tracked over 30 years.

A change in 5 degrees of temperature every day is called weather. However, a change in 5 degrees of average temperature over 30 years is called climate.

That’s why we have climate change and not weather change for long-term meteorological effects!

We often experience different climates as we travel across the globe. Europe would be generally cold even in summer and the Middle East would be sultry hot.

Knowing this gives us foresight on what to prepare.

We can ready our ships and request winter PPE before arrival in cold climates.

On another hand, stacking up plenty of drinking water, and making sure that the air conditioner is fully functional helps us a lot in hot climates.

Elements of Weather

For many sea folks, weather is a number one concern when sailing. I have captains who always update themselves with the weather. They are also very keen on the science of marine meteorology.

Careful observation of the meteorological elements coupled with printouts from the weather fax is enough to take a glimpse of what lies ahead.


The movement of air is called the wind. This element occurs due to pressure differences and unequal heating of the earth’s surface.

Their speed and direction give us a hint of what the sea and sky will do next.

Winds usually precede the state of the ocean. Watch Officers are often advised to call their captains whenever experiencing a sudden but very strong wind that lasts longer than expected.

One time, we had storm-force winds while at anchor in Pakistan. It was very unexpected and happened quickly. The winds topped at 60 knots for a few minutes. It died down as quickly as it came.

You can imagine how our Captain and our Chief Mate reacted when that happened. They were unprepared because it was not broadcast on the Navtex or any channels. Moreover, the engineers had just come up for dinner.

We just finished working on the mast at that time, too. It was 1700H when the wind started to pick up and the sea started getting foamy. It died down at around 1730H.

A Comfortmeter and a Barometer inside the bridge of a tanker ship
A Comfortmeter and a Barometer.


Another component of marine meteorology that we always observe is temperature. On board, we measure temperature using a thermometer placed outside the bridge.

Temperature tells us about the movement of the molecules in the air.

But another important reason why we measure temperature is that it affects the weather.

By observing the air temperature, we will have an understanding of the type of precipitation we may have (rain, snow, or sleet). Additionally, it affects wind speed and direction, relative humidity, and rate of evaporation.

I often notice that whenever there is a sudden change in temperature like the wind suddenly blows cooler, rain would fall afterward.

Atmospheric Pressure

In simple terms, atmospheric pressure is the weight of air around you. It is also called air pressure. It is the mass of the atmosphere per unit area as gravity pulls it to Earth.

Seafarers, particularly OOWs, normally record the atmospheric pressure using an aneroid barometer.

An Aneroid Barometer is a type of barometer that measures the weight of air or atmospheric pressure. It contains metallic parts such as the aneroid chamber, supporting springs, levers, a pointer, and the analog dial.

It is very important in marine meteorology since it is one of the most accurate ways to predict the weather.

A falling barometric pressure indicates a brewing storm or the presence of a storm. On the other hand, rising atmospheric pressure signals clear skies and calm weather.

Since we have high and low pressure, there is also a normal atmospheric pressure. That normal range is between 970 millibars (MB) to 1050MB.

The high-pressure area is often characterized by fair weather. Low-pressure areas are characterized by stormy weather.


Humidity is the amount of moisture present in the air. It doesn’t affect the sky that much but it informs us of the coming fog and precipitation.

Sometimes, I jokingly call humidity comfortability level, and the instrument used to measure our comfortability is called a comfort meter. This is because humidity affects our comfort.

A comfort meter is a device that measures temperature and humidity. Meanwhile, a device that specifically measures humidity is called a hygrometer.

Wet Bulb and Dry Bulb

We normally have a hygrometer on board consisting of two thermometers set up side by side called wet and dry bulb type. Their main function is to measure relative humidity and thus determine the dew point.

When we were in the Middle East, the temperature was very hot. But what’s worse was that the humidity was very high. We were sweating like a horse even without doing anything.

If you are in a bulk carrier and dew point is one of your concerns for your cargo, then understanding how humidity works is very important.

Even your paint job is affected whenever the humidity is too high. You will sometimes notice white spots on the area where you painted.

This is because the water formed on that surface while the paint was still warm.

Precipitation and atmospheric pressure systems in a weather chart.
Precipitation and atmospheric pressure systems. Image:


One of the most common components of marine meteorology that we easily understand is precipitation or rain.

When we talk about precipitation, it is any form of water that drops from the atmosphere to the Earth.

Liquid droplets, hail, snow, sleet, and drizzle are all forms of precipitation.

Precipitation is a part of the water cycle where water vapor turns into liquid from the atmosphere and falls back to the earth.

Going back to our elementary days, precipitation is part of the water cycle. It is also a useful tool in predicting the weather in marine meteorology.

Hot weather at sea evaporates water into the sky. They in turn create clouds which then give back the water through precipitation.

Heavy precipitation at sea greatly reduces visibility while diminishing the efficiency of our radar.


The last component of our weather element is cloudiness or simply the number of clouds present in the sky.

Clouds are small droplets of water or ice crystals in the atmosphere which are visible to the naked eye.

Cloudiness affects much of the precipitation and temperature around us. It is one major forecasting tool for seafarers while sailing on the high seas.

Heavy rains, thunderstorms, strong winds, and approaching calm weather can be predicted while observing cloud patterns in the sky.

Fast-moving clouds at low altitudes indicate an approaching weather system. And we all know that a dark nimbus cloud is a signal for incoming rain.

A clear sky in the evening is often followed by fair weather in the morning or even daytime.

These patterns occur throughout the year while some arrangements happen in specific months. There are just many things you can do with clouds and how to predict the weather.

Those six are the elements of weather. Together, they make up the state of the atmosphere at any given time.

Subtle changes to these elements are a precursor to a major occurrence. This is the reason why OOWs are keen on studying marine meteorology. They do this using simple tools and equipment some of which can be found at home.

Most of my Ship Captains pay attention to the weather changes around them. The keenest ones can usually tell specific conditions and often talk to weather charts, even predicting more accurately.

May the winds be in your favor.



Submit a Comment

Your email address will not be published. Required fields are marked *