{"id":867,"date":"2026-07-04T10:16:27","date_gmt":"2026-07-04T10:16:27","guid":{"rendered":"https:\/\/marinersupdate.com\/blog\/?p=867"},"modified":"2026-07-04T10:16:27","modified_gmt":"2026-07-04T10:16:27","slug":"captains-weather-desk-wk-6","status":"publish","type":"post","link":"https:\/\/marinersupdate.com\/blog\/captains-weather-desk-wk-6\/","title":{"rendered":"CAPTAIN&#8217;S WEATHER DESK \u2013 WK : 6"},"content":{"rendered":"\n<h1 class=\"wp-block-heading\">HUMIDITY AND CONDENSATION<\/h1>\n\n\n\n<h2 class=\"wp-block-heading\">Understanding Water Vapour, Dew Point and Relative Humidity<\/h2>\n\n\n\n<p>Humidity plays a vital role in the formation of clouds, fog, dew, mist, precipitation, and many other weather phenomena. Although water vapour is invisible, it is one of the most important components of the atmosphere because it directly influences weather conditions and the Earth&#8217;s energy balance.<\/p>\n\n\n\n<p>For mariners, understanding humidity and condensation is essential for interpreting weather changes, predicting fog formation, and recognising conditions that may affect navigation and visibility.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Water Vapour \u2013 The Invisible Moisture in the Atmosphere<\/h2>\n\n\n\n<p>Water vapour is water in its gaseous state and is always present in the atmosphere, although it cannot be seen. Its concentration varies from place to place and changes continuously with temperature and evaporation.<\/p>\n\n\n\n<p>The largest source of atmospheric water vapour is the evaporation of seawater. Smaller contributions come from lakes, rivers, wet soil, vegetation, snow, and ice.<\/p>\n\n\n\n<p>The amount of water vapour in the atmosphere is constantly changing as water evaporates, condenses, and falls back to the Earth&#8217;s surface through precipitation.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Water Vapour vs Clouds and Fog<\/h2>\n\n\n\n<p>Water vapour should not be confused with clouds or fog.<\/p>\n\n\n\n<p>Water vapour is an invisible gas, whereas clouds and fog are made up of countless tiny liquid water droplets or ice crystals that are visible to the human eye.<\/p>\n\n\n\n<p>Clouds form higher in the atmosphere, while fog forms near the Earth&#8217;s surface. Both are the result of water vapour condensing when the air becomes saturated.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Saturated and Unsaturated Air<\/h2>\n\n\n\n<p>The amount of water vapour that air can hold depends primarily on its temperature.<\/p>\n\n\n\n<p>Warm air can contain much more water vapour than cold air. As temperature increases, the air&#8217;s moisture-holding capacity also increases.<\/p>\n\n\n\n<p>When air contains the maximum amount of water vapour possible at a particular temperature, it is said to be <strong>saturated<\/strong>.<\/p>\n\n\n\n<p>If it contains less moisture than its maximum capacity, it is called <strong>unsaturated air<\/strong>.<\/p>\n\n\n\n<p>When unsaturated air cools, it gradually approaches saturation. If cooling continues beyond the saturation point, the excess water vapour changes into tiny liquid droplets or ice crystals through the process of <strong>condensation<\/strong>.<\/p>\n\n\n\n<p>This process produces weather phenomena such as:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Clouds<\/li>\n\n\n\n<li>Fog<\/li>\n\n\n\n<li>Mist<\/li>\n\n\n\n<li>Dew<\/li>\n\n\n\n<li>Frost<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Dew Point<\/h2>\n\n\n\n<p>The <strong>dew point<\/strong> is the temperature to which unsaturated air must be cooled in order to become saturated.<\/p>\n\n\n\n<p>As long as the amount of water vapour in the air remains unchanged, the dew point also remains constant, even if the air temperature changes.<\/p>\n\n\n\n<p>When the air temperature falls to the dew point, condensation begins.<\/p>\n\n\n\n<p>If the air is already saturated, the air temperature and the dew point are the same.<\/p>\n\n\n\n<p>Dew point is one of the most useful indicators of the amount of moisture present in the atmosphere.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Measuring Humidity<\/h2>\n\n\n\n<p>Humidity can be expressed in two commonly used ways.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Absolute Humidity<\/h3>\n\n\n\n<p>Absolute humidity is the actual mass of water vapour present in a given volume of air.<\/p>\n\n\n\n<p>It is usually expressed in <strong>grams per cubic metre (g\/m\u00b3)<\/strong>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Relative Humidity (RH)<\/h3>\n\n\n\n<p>Relative humidity compares the amount of water vapour currently present in the air with the maximum amount the air could hold at the same temperature.<\/p>\n\n\n\n<p>It is expressed as a percentage.<\/p>\n\n\n\n<p>For example:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"370\" height=\"61\" src=\"https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-3.png\" alt=\"\" class=\"wp-image-869\" style=\"width:765px;height:auto\" srcset=\"https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-3.png 370w, https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-3-300x49.png 300w, https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-3-230x38.png 230w, https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-3-350x58.png 350w\" sizes=\"auto, (max-width: 370px) 100vw, 370px\" \/><\/figure>\n\n\n\n<ul class=\"wp-block-list\">\n<li>RH = <strong>100%<\/strong> means the air is saturated.<\/li>\n\n\n\n<li>RH = <strong>50%<\/strong> means the air contains half of the moisture it could hold at that temperature.<\/li>\n<\/ul>\n\n\n\n<p>Relative humidity changes whenever air temperature changes, even if the amount of water vapour remains the same.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Understanding Humidity with an Example<\/h2>\n\n\n\n<p>Consider air at <strong>40\u00b0C<\/strong> containing <strong>20 g\/m\u00b3<\/strong> of water vapour.<\/p>\n\n\n\n<p>At 40\u00b0C, air can hold approximately <strong>50 g\/m\u00b3<\/strong>, giving a <strong>relative humidity of 40%<\/strong>.<\/p>\n\n\n\n<p>If this air cools to about <strong>20\u00b0C<\/strong>, it becomes saturated because warm air can no longer hold the same amount of moisture.<\/p>\n\n\n\n<p>Therefore:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Dew Point = 20\u00b0C<\/strong><\/li>\n<\/ul>\n\n\n\n<p>If the air cools further to <strong>10\u00b0C<\/strong>, its moisture-holding capacity decreases even more.<\/p>\n\n\n\n<p>The excess water vapour condenses into tiny droplets, producing fog, mist, cloud, or dew.<\/p>\n\n\n\n<p>The greater the initial moisture content, the greater the amount of condensation produced during cooling.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">The Relationship Between Temperature and Humidity<\/h2>\n\n\n\n<p>The saturation curve clearly shows that warmer air can hold much more water vapour than colder air.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"504\" height=\"299\" src=\"https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-2.png\" alt=\"\" class=\"wp-image-868\" srcset=\"https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-2.png 504w, https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-2-300x178.png 300w, https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-2-230x136.png 230w, https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-2-350x208.png 350w, https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/image-2-480x285.png 480w\" sizes=\"auto, (max-width: 504px) 100vw, 504px\" \/><\/figure>\n\n\n\n<p>For example:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>At <strong>20\u00b0C<\/strong>, air can hold approximately <strong>20 g\/m\u00b3<\/strong> of water vapour.<\/li>\n\n\n\n<li>At <strong>40\u00b0C<\/strong>, it can hold about <strong>50 g\/m\u00b3<\/strong>.<\/li>\n<\/ul>\n\n\n\n<p>This explains why tropical regions often experience high humidity, while colder regions generally contain much less atmospheric moisture.<\/p>\n\n\n\n<p>It also explains why cooling warm, moist air frequently results in condensation and cloud formation.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Why This Matters to Mariners<\/h2>\n\n\n\n<p>Humidity is far more than just a measure of moisture in the air\u2014it is a key factor influencing weather development.<\/p>\n\n\n\n<p>Understanding humidity and condensation helps mariners anticipate:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Fog formation<\/li>\n\n\n\n<li>Cloud development<\/li>\n\n\n\n<li>Reduced visibility<\/li>\n\n\n\n<li>Dew and frost<\/li>\n\n\n\n<li>Rainfall potential<\/li>\n\n\n\n<li>Atmospheric stability<\/li>\n<\/ul>\n\n\n\n<p>A sound knowledge of these concepts enables better interpretation of marine weather forecasts and improves situational awareness during voyage planning and navigation.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Key Takeaways<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Water vapour is an invisible gas that is always present in the atmosphere.<\/li>\n\n\n\n<li>Clouds and fog are visible droplets formed through condensation.<\/li>\n\n\n\n<li>Warm air can hold more moisture than cold air.<\/li>\n\n\n\n<li>Saturated air contains the maximum amount of water vapour possible at a given temperature.<\/li>\n\n\n\n<li>The dew point is the temperature at which condensation begins.<\/li>\n\n\n\n<li>Absolute humidity measures the actual amount of water vapour in the air.<\/li>\n\n\n\n<li>Relative humidity compares the current moisture content with the maximum possible at the same temperature.<\/li>\n\n\n\n<li>Cooling air below its dew point leads to condensation, forming clouds, fog, mist, or dew.<\/li>\n\n\n\n<li>Understanding humidity is essential for predicting weather and improving maritime decision-making<\/li>\n<\/ul>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>HUMIDITY AND CONDENSATION Understanding Water Vapour, Dew Point and Relative Humidity Humidity plays a vital role in the formation of clouds, fog, dew, mist, precipitation, and many other weather phenomena. Although water vapour is invisible, it is one of the most important components of the atmosphere because it directly influences [&hellip;]<\/p>\n","protected":false},"author":3,"featured_media":870,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[584],"tags":[831,692,889,890,888,587,594,592,585,593,891,697,213,595,586],"class_list":["post-867","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-captains-weather-desk","tag-atmosphericscience","tag-captainsweatherdesk","tag-condensation","tag-dewpoint","tag-humidity","tag-marinemeteorology","tag-marinetraining","tag-maritimeeducation","tag-meteorology","tag-oceanweather","tag-relativehumidity","tag-seafarerknowledge","tag-shippingindustry","tag-weatherawareness","tag-weatherscience"],"featured_image_src":"https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/CAPTAIN-COVER-6-1024x576.png","blog_images":{"medium":"https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/CAPTAIN-COVER-6-300x169.png","large":"https:\/\/marinersupdate.com\/blog\/wp-content\/uploads\/2026\/07\/CAPTAIN-COVER-6-1024x576.png"},"ams_acf":[],"_links":{"self":[{"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/posts\/867","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/comments?post=867"}],"version-history":[{"count":1,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/posts\/867\/revisions"}],"predecessor-version":[{"id":871,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/posts\/867\/revisions\/871"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/media\/870"}],"wp:attachment":[{"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/media?parent=867"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/categories?post=867"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/marinersupdate.com\/blog\/wp-json\/wp\/v2\/tags?post=867"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}