What does the terminology in the Shipping Forecast mean?
The Shipping Forecast, which is provided by the Met Office (under a contract with the UK Maritime and Coastguard Agency), and broadcast four times daily on BBC Radio 4, is highly structured to maximise the use of the available time. The basic order of the forecast is:
- GALE WARNINGS IN FORCE
- GENERAL SITUATION
- AREA FORECASTS: WIND DIRECTION/SPEED: (SEA STATES**): WEATHER: VISIBILITY: (SHIP ICING IF APPROPRIATE)
- COASTAL WEATHER REPORTS AROUND BRITISH/IRISH COASTS (*)
(*) From April 6th, 1998, certain bulletins no longer carry coastal weather reports.
(**) from 2006, some versions of the bulletin under header FPUK71 EGRR have included sea states.
Most of the forecast is self-explanatory, but in the synoptic preamble, and in the weather reports which follows, some terms are used which may not be familiar.
Movement of pressure centres: (in forecast preamble/general situation)
|Slowly||up to 15 knots||(approx: up to 8 m/s or 28 km/hr)|
|Steadily||15 - 25 knots||(approx: 8 - 13 m/s or 28 - 46 km/hr)|
|Rather quickly||25 - 35 knots||(approx: 13 - 18 m/s or 46 - 65 km/hr)|
|Rapidly||35 - 45 knots||(approx: 18 - 23 m/s or 65 - 83 km/hr)|
|Very rapidly||over 45 knots||(approx: over 23 m/s or 83 km/hr)|
Pressure changes:(in coastal station reports/3 hours is a 'standard' time period used in synoptic meteorology in mid/high latitudes.)
|Steady||Change less than 0.1 mbar in past 3 hours|
|Rising/Falling slowly||Change 0.1 to 1.5 mbar in past 3 hours|
|Rising/Falling||Change 1.6 to 3.5 mbar in past 3 hours|
|Rising/Falling quickly||Change 3.6 to 6.0 mbar in past 3 hours|
|Rising/Falling very rapidly||Change more than 6.0 mbar in past 3 hours|
Veering/Backing of wind: When a wind direction changes such that it moves with the clock, e.g. from east to south through south-east, that is a veering wind; A wind therefore that changes against the normal clock motion is a backing wind.
...and for the visibility categories the following apply:
|FOG||< 1 km||< 1100 yds|
|POOR||1 to 3.9 km||1100 yds to 2 nautical miles|
|MODERATE||4 to 9 km||2 to 5 nautical miles|
|GOOD||>=10 km||> 5 nautical miles|
Since 2006, sea states (strictly wind-wave forecasts) have been included in some versions of the bulletin: they employ a crude relationship between the forecast wind and expected wind wave heights (mean of a well-formed wave train) IN OPEN WATER. The categories are as under:-
|Description ||Height in metres|
|Calm||0.1 or less|
|Smooth||>0.1 to 0.5|
|Slight||>0.5 to 1.25|
|Moderate||>1.25 to 2.5|
|Rough||>2.5 to 4.0|
|Very rough||>4.0 to 6.0|
|High||>6.0 to 9.0|
|Very high||>9.0 to 14.0|