Meteorological Jargon Explained

27 May 2010 By David Cannon, Weather Routing Inc.

Weather is an important part of trip planning for mariners and vacationers alike. But sometimes when listening to or reading weather reports, do you find yourself scratching your head?

We, as Meteorologists, as well as those seasoned veterans of the sea, are certainly familiar with the nomenclature and definition of weather features and phenomena, but do we all know the difference between, say, an Extratropical Cyclone and a Tropical Cyclone, or for that matter a Subtropical Cyclone? In order to understand the differences, you must understand the anatomy of these storms and how they relate to one another.

A Tropical Cyclone (a Tropical Depression or Tropical Storm for example) is defined as a warm core system, in which temperatures are warmer near the center of the cyclone than at the periphery and is found in lower, tropical latitudes.

Intense squalls associated with these systems are commonly collocated and the centers of the cyclones are tightly wound; the strongest winds typically are found closer to the center of the system. In the case of a hurricane, typically there is an eye wall, a band of very intense squalls surrounding the eye itself. It is within this fairly narrow band of squalls that the most intense winds are usually found. Tropical cyclones generally derive their energy from warm water and lighter winds aloft, which develop and expand the squalls, allowing them to sustain themselves.

Over time, tropical cyclones lose their characteristics and become Extratropical Cyclones. Unlike their tropical counterparts, Extratropical Cyclones are cold core systems; the temperatures near the centers of these systems are colder. Temperatures increase as the storm radiates out. Further, Extratropical Cyclones do not derive their energy from warm water, nor from lighter winds aloft and they tend to be extensive systems. The large gales and storms often seen in the North Atlantic and North Pacific are examples of Extratropical Cyclones and especially can be seen during the winter season. The strongest of these winds tends to be farther removed from the center of the cyclone and often extend several hundred miles away from the center.

Subtropical Cyclones are also known as “hybrid systems”, meaning they tend to show the characteristics of both tropical and Extratropical Cyclones. They tend to exhibit warmer temperatures near the center of the system, but the strongest winds tend to be found farther away from the center (as with Extratropical systems). When viewed via satellite imagery, the cloud pattern is usually in the form of an “S”; this often indicatives stronger winds aloft, which keep associated squalls farther away from the center.

Other meteorological terms explained:

Thermal Lows
Also known as "heat lows” are generated due to thermal differences between land and sea (most commonly found on the west coasts of continents).

Blocking High

A slow-moving high (a "warm" ridge aloft and a "cold" ridge at the surface), which causes a "split" in the westerly winds aloft. Such highs are very slow-moving, preventing or "blocking" the progress of migratory cyclones across their latitudes.

Bermuda High

Commonly found during the Northern Hemisphere during the summer months, this is a semi-permanent feature, centered in the western Atlantic that migrates eastward/westward with varying central pressures (related term: Azores High, which is more commonly found near the Azores during other times of the year).

Zonal Flow

A flow of predominately west to east winds aloft

Meridional Flow

A flow of winds aloft that has more southerly and northerly components to their direction, very commonly found with large high and low pressure systems aloft.

With the 2010 Atlantic and Pacific Hurricane Seasons pending, it’s important to understand the composition of these storms and have a firm grasp on meteorological terms so you know what you’re facing on the high seas.

David Cannon is Yacht Operations Manager and Senior Meteorologist at Weather Routing Inc. which has provided weather forecasts and meteorological consultation for clients worldwide since 1961. Contact Dave Cannon at 1-518-798-1110;;

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