Sea Temperatures FAQ

What is sea temperature?

When we talk about sea temperature, we are generally interested in the sea surface temperature or SST. While this obviously refers the water temperature close to the surface there isn't actually an officially agreed upon definition of how close.

There are several measures of sea surface temperature, all of which have their advantages and disadvantages. There are those that measure the absolute surface, those measuring just below the skin and those around a metre below the surface. The first two have the advantage that they can be measured by satellite, while the third is less affected by fluctuations caused by air temperature or the sun's heat. Unfortunately to measure more than a few millimetres under the sea’s surface cannot be done remotely.

This website uses data from satellites such as NASA's Aqua which is processed by the NOAA to provide what they term near sea surface temperature or NSST.

What affects sea temperatures?

Sea temperatures are influenced by a range of factors. These include the sun's heat, ocean currents, wind patterns, and the depth of the water. Seasonal changes and geographical location also play significant roles.

Does the sea temperature change throughout the day?

The temperature of the sea is highly sensitive to ambient atmospheric conditions which may cause it to vary significantly depending on time of day and near-surface depth.

A further factor affecting inshore water temperatures are the tides. If it is a hot day the land will be heated up which will be transferred to the sea as the tide comes in.

Why do sea temperatures vary between different locations?

Sea temperatures can vary due to differences in ambient temperature, ocean currents, and depth. For example, tropical waters are generally warmer than polar regions which seems fairly obvious, given the differences in climate.

Less obvious is the effect of oceanic currents. The best known of these, the Gulf Stream, carries warm water to higher latitudes, affecting local sea temperatures. So areas such as the north west coast of Scotland have higher sea temperatures than one might expect.

How are sea temperatures measured?

Sea temperatures are measured using a variety of methods. The most simple is by directly measuring the temperature of the seawater. Buoys and ships use thermometers placed in the water, although the depth at which this is measured will vary, leading to inconsistencies.

These days most data comes from satellites which measure the sea surface temperature using an array of infrared and microwave sensors.

Why do different sources give different sea temperatures?

On this website we use satellite data, but will also provide live buoy data where available. You may notice that these measurements can vary, and sometimes by a couple of degrees.

There are a few reasons for this. Our primary satellite data is updated daily and is measured in such a way to eliminate a degree of the daily (diurnal) fluctuation. This can be caused by the sun heating the water surface through the day, or the tide coming in over hot sand for example. Another reason is the depth at which the temperature is measured. The satellite measures the very top surface, the skin and subskin, whereas the buoy is a little deeper at around a metre depth.

How do sea temperatures change with depth?

Sea temperatures generally decrease with depth - the deeper you go the colder it is. The surface layer, known as the mixed layer, is the warmest due to the effects of direct sunlight and air temperature. Below this, the temperature drops sharply in the thermocline layer and continues to decrease slowly in the deep ocean.

The deep ocean, i.e. below 200 metres (600ft) is cold wherever you are. On average it is only 4°C (39°F).

Why are sea temperatures important for weather forecasting?

Sea temperatures are crucial for weather forecasting because they influence atmospheric conditions. Warm sea temperatures can lead to the formation of hurricanes and typhoons, while cooler temperatures can affect weather patterns and precipitation.

What is the average sea temperature globally?

The average sea temperature around the world varies, but appears to be on an upward trend. The average sea surface temperature is defined over the global ocean, from 60°S to 60°N, i.e. not including polar regions. The sea temperature reached a record 21.09°C at the end of February 2024.

How do climate change and global warming affect sea temperatures?

Climate change and global warming are causing sea temperatures to rise. This warming affects marine ecosystems, contributes to the melting of polar ice, and can lead to more extreme weather events like hurricanes and typhoons. 

A degree or half a degree rise in sea temperature may not sound like much, but when converted into energy terms, given the size of the oceans, it is huge.

Why do sea temperatures feel different from air temperatures?

Water has a higher heat capacity than air, meaning it can absorb and retain more heat and it does so more rapidly. Therefore, sea temperatures change more slowly than air temperatures. Additionally, the body loses heat faster in water than in air, making the sea often feel colder than the surrounding air.

Where are the highest sea temperatures in the world?

It would be fair to assume that the warmest seas are found within the tropics, and this is certainly the case. As it stands the sea very rarely breaches the 100°F (37.8°C) mark. In fact, until recently it seems this had never been recorded. Consistently topping the hot water charts has been the Bay of Kuwait in the Persian Gulf at a  maximum 37.6°C (99°F).

However, recently it has been another gulf that has broken this record and surpassed the 100°F mark. Manatee Bay on Florida's Gulf of Mexico coast, apparently hit 101 degrees Fahrenheit (38.4 degrees Celsius) recently.

What tools are used to predict future sea temperatures?

Scientists use climate models, historical data, and satellite observations to predict future sea temperatures. These models consider various factors like greenhouse gas emissions, ocean currents, and atmospheric conditions.