Meteorological Terms

A quick summary of meteorological terms that RYA Advanced Powerboat and Yachtmaster (Coastal and Offshore) exam candidates should refresh before their practical exam. Some of the these “met. terms” are covered at RYA Day Skipper Shorebased. Some are covered at RYA Yachtmaster Offshore Shorebased.

VISIBILITY DEFINITIONS

TERM DEFINITION
Very Poor (Fog) * Visibility less than 1,000 metres
Poor * Visibility between 1,000 metres and 2 nautical miles
Moderate * Visibility between 2 and 5 nautical miles
Good * Visibility more than 5 nautical miles

Example: “Visibility- Moderate”

WEATHER TIMING DEFINITIONS

TERM DEFINITION
Imminent * Expected within six hours of time of issue
Soon * Expected within six to 12 hours of time of issue
Later * Expected more than 12 hours from time of issue

Example: “Moderate Visibility, Later.”

WIND WARNINGS DEFINITIONS

TERM DEFINITION
Strong Wind * Winds of force 6
Gale * Winds of force 8
Severe Gale * Winds of force 9
Storm * Winds of force 10
Violent Storm * Winds of force 11
Hurricane Force * Winds of force 12

Example: “A Strong wind warning is in force for sea areas, Dover, Wight, Portland and Plymouth”

WIND FORECASTING TERMS

TERM DEFINITION
Veering * The changing of the wind direction clockwise, e.g. E to S
Backing * The changing of the wind in the opposite direction to veering (anticlockwise), e.g. E to N
Becoming Cyclonic * Indicates that there will be considerable change in wind direction across the path of a depression within the forecast area

Example: “Southerly Gale force winds will veer, and increase South West Force 9 gusting 10”

TIMING IN MARINE WEATHER FORECASTS

TERM DEFINITION
Imminent * Expected within six hours of time of issue
Soon * Expected within six to 12 hours of time of issue
Becoming Cyclonic * Indicates that there will be considerable change in wind direction across the path of a depression within the forecast area

Example: “Southerly Gale force winds will veer South West Later, VISIBILITY- Moderate or poor, becoming good later.”

SEA STATE TERMS / DEFINITIONS

TERM DEFINITION
Smooth * Wave height less than 0.5 m
Slight * Wave height of 0.5 to 1.25 m
Moderate * Wave height of 1.25 to 2.5 m
Rough * Wave height of 2.5 to 4.0 m
Very Rough * Wave height of 4.0 to 6.0 m
High * Wave height of 6.0 to 9.0 m
Very High * Wave height of 9.0 to 14.0 m
Phenomenal * Wave height more than 14.0 m

Example: “SEA STATE- Moderate or rough West of Orkney, slight or moderate elsewhere.”

MOVEMENT OF PRESSURE SYSTEMS

Slowly * Moving at less than 15 knots
Steadily * Moving at 15 to 25 knots
Rather Quickly * Moving at 25 to 35 knots
Rapidly * Moving at 35 to 45 knots
Vert Rapidly * Moving at more than 45 knots

PRESSURE TENDENCY DEFINITIONS

Rising (or falling) more slowly * Pressure rising (or falling) at a progressively slower rate through the preceding three hours
Rising (or falling) slowly * Pressure change of 0.1 to 1.5 hPa in the preceding three hours
Rising (or falling) * Pressure change of 1.6 to 3.5 hPa in the preceding three hours
Rising (or falling) quickly * Pressure change of 3.6 to 6.0 hPa in the preceding three hours
Rising (or falling) very rapidly * Pressure change of more than 6.0 hPa in the preceding three hours
Now Rising (or falling) * Pressure has been falling (rising) or steady in the preceding three hours, but at the time of observation was definitely rising (falling)

Note: 1 hPa = 1 mb

DOUG’S COMMENT FOR EXAM CANDIDATES

The observant reader will have noticed that each term has a coloured dot next to it. Either * or *.

I would suggest that Advanced Powerboat and Yachtmaster Coastal, Exam candidates should as a minimum know all of the definitions marked with a *, however strong candidates might also know some of those married with a *. (If however your examiner feels differently then don’t blame me!)

I suggest that a strong Yachtmaster Offshore candidate would know all of the * terms and the vast majority, if not all of the * terms.

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