Gale Warning Terminology:The description of gales is in accordance with internationally agreed definitions. However, the UK Met Office also issues gales using gust criteria even when the mean speed is below gale force as below:
Gale Winds of at least Beaufort force 8 (34-40 knots) or gusts reaching 43-51 knots
Severe gale Winds of force 9 (41-47 knots) or gusts reaching 52-60 knots
Storm Winds of force 10 (48-55 knots) or gusts reaching 61-68 knots
Violent storm Winds of force 11 (56-63 knots) or gusts of 69 knots or more
Hurricane force * Winds of force 12 (64 knots or more
* Note: The term used is "hurricane force", However the term "hurricane" on its own means an intense tropical cyclone of the kind that affects the Caribbean and Eastern Pacific. In the China Sea, it would be called a typhoon. Such tropical cyclones are not experienced in British waters. In that sense, Mike Fish was correct in 1987, although winds did reach Hurricane force! This is not a case of semantics it was a very deep low that deepened rapidly. Nevertheless. to a meteorologist it was not a hurricane.
Gale Warning Timing:The UK uses the following terms to indicate the expected times of onset of a gale:
Imminent Expect within 6 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
Perhaps Later * Used when a gale is considered possible in the "later" period, but the forecaster is not sufficiently sure to issue a warning.
* Note: If there is doubt about gales in the immediate or soon category, then the forecast may say "perhaps locally" or some such phrase, BUT a warning MUST be issued
Visibility:These are internationally agreed definitions of visibility. NOTE - these relate to the usage. Over land, for driving a vehicle, a fog would be below 200 m.
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
Movement of Pressure Systems:These terms are used in the synopsis to describe speed of movement of weather patterns:
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
Very rapidly Moving at more than 45 knots
Pressure Tendency in station reportsReports from coastal stations and Light vessels or buoys will give the pressure and a description of how the pressure has been changing.
Rising (or falling) slowly Pressure change of 0.1 to 1.5 mb in the preceding three hours
Rising (or falling) Pressure change of 1.6 to 3.5 mb in the preceding three hours
Rising (or falling) quickly Pressure change of 3.6 to 6.0 mb in the preceding three hours
Rising (or falling) v. rapidly Pressure change of more than 6.0 mb 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)
WindNote that wind and current use different conventions. A wind blows FROM the stated direction. Currents are described as the direction that they are going TO. We talk about and East going tide
Wind direction Indicates the direction from which the wind is blowing
Becoming cyclonic Indicates that there will be considerable change in wind direction across the path of a depression within the forecast area
Veering The changing of the wind direction clockwise, e.g. SW to W
Backing The changing of the wind in the opposite direction to veering (anticlockwise), e.g. SE to E
Beauford Wind Force ScaleThe scale was created in 1806 by Sir Francis Beaufort, an Irish born British admiral and hydrographer. It is used to scale is an empirical measure for describing wind speed based mainly on sea observations. The scale is reproduced in the following article:
http://en.wikipedia.org/wiki/Beaufort_scale Sea StateSmooth 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
