On the Job

Understanding Weather at Sea

23 September 2021 By Ted Morley
boats in lightning storm

Capt. Ted Morley was raised aboard a schooner and has made a career working on board vessels ranging from superyachts to super tankers. During his tenure at sea, he worked his way up from seaman to master. He currently holds a USCG Master’s License, Unlimited Tonnage as well as several foreign certificates. Capt. Morley actively participates in maritime advisory committees in the U.S. as well as overseas and is involved in regulatory policy review in the U.S.. 

The USCG, MCA, and a host of other flag states, through the IMO STCW Convention, set mandatory training for mariners. The requirements as defined in STCW A-II/1 and SCTW A-II/2, as well as those in the US 46 CFR 11.309(a)(4)(xiii) for an STCW endorsement as Officer in Charge of a navigational watch on vessels of 500 or more gross tonnage (ITC), outline training and assessment in Meteorology and Seamanship.

Weather is constantly changing, and you need to be aware of what those changes can cause. It’s vital to a successful voyage that you understand forecasting and the dramatic increase in energy as wind speeds increase.

Weather fronts and low-pressure systems can move quickly. Watching the ship’s barometer for a change will give you an idea of the weather ahead: as the pressure drops, the wind builds as the atmosphere works to adjust to the change.

You need to understand the stages of a storm as they develop, mature, and decay. During this cycle, you can get very high winds as outflow increases with high altitude air dropping through the storm in downdrafts, creating intense weather conditions within the storms. These downdrafts and temperature changes are what help create tornadoes and microbursts in a thunderstorm — which can grow laterally in the decay phase as the storm collapses downward and outward, quickly closing the distance and violently increasing impact.

Watching the ship’s barometer for a change will give you an idea of the weather ahead: as the pressure drops, the wind builds as the atmosphere works to adjust to the change.

A weather front is basically an area between two distinct air masses of different densities and temperatures. This area, and the turbulence it creates in the atmosphere, is where storms typically are generated. When a cold front is passing, you may notice a sudden drop in temperature with heavy rain and thunderstorms developing. Why? Basically, as the warm air rises, it cools. Cooler air cannot retain as much moisture as warm air so the droplets form clouds. A cold front will often have a narrow band of rain along its leading edge that are often very strong and can bring severe thunderstorms, hail, snow, and tornadoes. After a cold front passes, the weather is typically drier and clear as high pressure builds behind it.

Modern satellites, modeling, prognostic charts, and weather instruments are designed to give us more details on developing systems. But nothing replaces a well-trained and experienced mariner. Planning a voyage and operating a vessel requires a knowledge of weather, which is why the training regulations exist. However, they represent the minimum standards required. Try to develop a deeper understanding of the factors that affect your life and the lives of those around you.

This article originally ran in the August 2021 issue of Dockwalk.


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