shipping forecast

1. GALE WARNINGS: A listing of all sea areas where gale warnings are in operation. These are also broadcast on BBC Radio 4 at the first programe break following their receipt and at the end of the hourly news bulletin. Coast Radio Stations also broadcast gale warnings for adjacent sea areas soon after receiving them.

2. GENERAL SYNOPSIS: An account of the development and the movement of depressions and anticyclones (also when time permits, of fronts affecting the sea areas around the British Isles and North West Europe.

3. FORECASTS BY SEA AREAS: Some Sea Areas are grouped together, but always following the same order, which is clockwise around the British Isles, beginning with Viking to the North East and ending with South East Iceland.
The forecast by areas gives:-
a) Expected wind directions, Beaufort forces and changes.
b) The weather.
c) Visibility for the 24 hour period following the broadcast.



4. ACTUAL WEATHER OBSERVATIONS: This information is obtained from various "Coastal Stations" situated around the British Isles and comprises:- Wind, Weather, Visibility, Barometer Pressure & Tendency, recently observed at the stations. See Sample Forecast
Terminology used in the Shipping Forecast
ANTICYCLONE: Area of high pressure, around which the wind moves in a clockwise direction, with the wind speed usually decreasing towards the centre, where winds are light and variable.

DEPRESSION: Area of low pressure, around which the wind moves in an anti-clockwise direction, with the wind speed increasing towards the centre, often resulting in gales.

SPEED & MOVEMENT OF HIGH & LOW PRESSURE FEATURES: The speed and movement of highs and lows given in the general synopsis, are described either by the "from" and "to" positions (Sea Areas), or by the use of the following terms:-

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 over 45 knots

Depressions generally move eastward (though the track may sometimes be in any direction). The movement of a developing "Low" will usually be parallel to the isobars in it's warm sector, that normally towards the East Northeast. When occlusion is well developed, the Low will turn poleward and decelerate, eventually becoming slow moving as it decays over a further one or two days.

Anticyclones movements are even more variable. Commonly very sluggish, some Highs may remain almost stationary for days or maybe weeks. Large Highs, typically elliptical in shape, can appear to move a considerable distance. This is due to a local build up in pressure on one of the ridges and a fall in pressure over the original centre. This causes the "centre of gravity" to shift and completely alters the wind directions in the central area of the high.
Some small Highs are escorted by very "active" Lows to the front and rear. These Highs will travel at the same speed as the escorting Lows and are commonly very windy.

Wind always moves from a High to a Low pressure area.

BACKING: A Backing wind moves anti-clockwise.

VEERING: A Veering wind moves clockwise.

CYCLONIC: This means that wind changes will be consistent with the anti-clockwise rotation around a depression.

WEATHER: Described as Fair, Rain, Showers, Drizzle, Snow or Extensive Fog as appropriate.

SHOWERS: This covers the whole range from light showers to thunderstorms which are localised and typically last for half an hour or so.

RAIN: Means continuous and widespread precipitation, associated with fronts and depressions.

SQUALLY SHOWERS: (When strong winds are otherwise not forecast) This means that gusts of wind or squalls associated with the showers, will far exceed the forecast wind speed.
(Typically reaching 30 knots - Force 6 to 7 and sometimes more)

VISIBILITY: The terms explained...

GOOD Means more than 5 Nautical Miles
MODERATE Means 2 to 5 Nautical Miles
POOR Means 1,000 metres to 2 Nautical Miles
FOG Means less than 1,000 metres

TIME PERIODS: The terms explained...

IMMINENT Means within 6 hours of the time issued
SOON Means within 6 to 12 hours of the time issued
LATER Means more than 12 hours from the time issued

PRESSURE TENDENCY: The terms explained...

Falling or Rising - Slowly = 0.1 to 1.5mb change
Falling or Rising - 1.6 to 3.5mb change
Falling or Rising - Quickly = 3.6 to 6.0mb change
Falling or Rising - V.Rapidly = more than a 6.0mb change

The last two are significant with falling pressure as they probably indicate that strong winds or gales will follow.

LOCATING THE DEPRESSION: In the Northern Hemisphere, facing into the wind, the centre of the depression is on your right.