{"id":801,"date":"2026-05-28T14:43:10","date_gmt":"2026-05-28T14:43:10","guid":{"rendered":"https:\/\/yachtersworld.com\/?p=801"},"modified":"2026-05-28T14:43:10","modified_gmt":"2026-05-28T14:43:10","slug":"how-to-use-a-barometer-to-understand-weather-and-why-you-should-never-tap-it","status":"publish","type":"post","link":"https:\/\/yachtersworld.com\/?p=801","title":{"rendered":"How to use a barometer to understand weather (and why you should NEVER tap it!)"},"content":{"rendered":"

Weather forecaster for the British Sailing Team since 2015, Simon Rowell, gives his advice on using a barometer to understand the forecast<\/strong><\/p>\n

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Most yachts have a mechanical barometer on board, either a brass or a stainless one screwed to the bulkhead somewhere convenient \u2013 ideally close to the navigation desk so it can be read while doing the log. These often get tapped before the reading is noted, so as \u2018to unstick the needle\u2019.<\/p>\n

A meteorologist\u2019s plea: DON\u2019T TAP YOUR BAROMETER!<\/p>\n

This is because it\u2019s a delicate mechanical instrument, and all you do when you tap it is to put an unknown error onto the reading. Almost all yacht barometers are uncalibrated, but that doesn\u2019t matter because you\u2019re not interested in the absolute value, just the rate of change of pressure, either up or down.<\/p>\n

Modern weather forecasting sources have become very good, with the Met Office and other similar agencies around the world giving generally reliable forecasts. In these forecasts the \u2018what\u2019 of the forecast is usually predicted accurately, eg a low pressure system bringing south-west 20-25 knots, veering north-west 15-20 knots as the front arrives.<\/p>\n

The part of the forecast that usually has the most error, particularly with unstable systems like depressions, is the \u2018when\u2019. That front may come over earlier or later than expected. This is why it\u2019s really important when getting your forecast for the day to think about what you can see, measure or feel as the weather comes through.<\/p>\n

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Mechanical barometers still play a valuable role on very technical yachts. Photo: Tatiana Dyuvbanova\/Alamy<\/p>\n<\/div>\n

With depressions there\u2019s a well known sequence of events. Usually in the northern hemisphere if a low is passing over we expect a sequence of: warm front; then a fairly steady \u2013 if grey and possibly wet \u2013 warm sector; and behind this the more active cold front with associated squally showers. Behind that there\u2019s usually the colder, drier air coming down from the north-west, which will often feel warmer due to the fact that the sun\u2019s out.<\/p>\n

If you\u2019re expecting this common sequence, then you\u2019ll also have the forecast arrival times of the fronts. Try and translate those forecast times into what you can see (a lowering and thickening progression of clouds) and what you can measure \u2013 most obviously your barometer will be falling.<\/p>\n

While you can\u2019t use the barometer reading as an exact value (because it\u2019s probably been tapped\u2026) you can measure the drop, and compare that to the expected drop from the forecast.<\/p>\n

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Plunging and rising barometric pressures as Storm Goretti passed over the Brambles Bank in the Solent in early January 2026<\/p>\n<\/div>\n

Rate of change<\/h2>\n

The rate of change of pressure is a very important metric, and is one of the main reasons to do hourly log readings even in waters you\u2019re very familiar with.<\/p>\n

The Shipping Forecast uses the following terms to describe pressure tendency:<\/p>\n