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Weather - Beaufort Scale, Forecasts

The weather and tides are  the biggest influences on your  motoring and sailing.  

Tides can be predicted;  weather can be forecast - but not always accurately.  However, you should get the best possible information available before going out. Forecasts are available from the BBC (Shipping and Inshore forecasts), Local radio, TV, newspapers, web, Coastguard via VHF,  Navtex - Navtex example (radio data transmission), mobile phone voice or text....

Met Office Shipping Forecasts

Bear in mind there are other countries for UK areas eg Norway  and France

Weather forecast forms (WORD document) - Weather forecast

Click here for RYA / Met Office sea areas and forecast chart:  Met Maps  (pdf format).  Geostrophic Scales enable you to estimate the wind speed from the separation of the isobars (lines of equal pressure)

Always write down the forecast, everyone will have a different memory of it!  If you can build up the picture by sketching in the pressure systems and wind directions it helps.  Preferably start this a few days before a long passage.

Shipping Forecast

The forecast is always given in the sequence below.  All the terms have specific meanings, given below

"THE SHIPPING FORECAST ISSUED BY THE MET OFFICE AT 0505 ON SATURDAY 23 OCTOBER 2004

THERE ARE WARNINGS OF GALES IN DOGGER GERMAN BIGHT HUMBER THAMES DOVER WIGHT PORTLAND PLYMOUTH BISCAY TRAFALGAR FITZROY SOLE LUNDY AND FASTNET

THE GENERAL SYNOPSIS AT 0100
LOW VIKING 990 MOVING SLOWLY EAST AND FILLING. LOW 200 MILES WEST OF FITZROY 988 MOVING RATHER QUICKLY NORTHEAST, EXPECTED SHANNON 984 BY 0100 SUNDAY

THE AREA FORECASTS FOR THE NEXT 24 HOURS
VIKING NORTH UTSIRE
CYCLONIC 4 OR 5 BECOMING NORTH OR NORTHWEST 3 OR 4. SHOWERS. GOOD"  

Weather reports from Coastal Stations gives the current conditions around the coats, this is helpful to get the current picture

The Inshore Waters Forecast (up to 12 miles off the coast) is in the format:

Wind: north or northwest 3, occasionally 4 in northwest, veering east or northeast 3 or 4 later.
Weather: scattered showers in north.
Visibility: good.
Sea State: in north, rough becoming moderate; in east, moderate becoming slight
Outlook for the following 24 hours:
Wind: northeast 3 or 4 increasing 4 or 5, perhaps 6 later in east.
Weather: scattered showers in north; occasional rain in south
Visibility: mainly good, perhaps becoming moderate in south.
Sea State: slight or moderate becoming moderate or rough

Weather Forecast Terms

Gale Warnings

Pressure System - speed of movement

Imminent 

within 6 hours of issue of warning

Slowly

up to 15 kn

Soon

from 6 -12 hours of issue of warning

Steadily

15-25 kn

Later

after 12 hours of issue of warning

Rather quickly

25-35 kn

 

Rapidly

35-45 kn


Pressure Tendency


Visibility

Steady

< 0.1 mb in 3 hrs

Very poor (fog)

< 1000 metres

Slowly

0.1 to 1.5 mb in 3 hrs

Poor

<2 Miles

Quickly

3.6 - 6.0 mb in 3 hrs

Moderate

2 - 5 Miles

Very Rapidly

> 6.0 mb in 3 hrs  (= gales)

Good

> 5 Miles

 

Sea State

Wave height

 Weather

Smooth

0.2 – 0.5m

Fair = No significant precipitation

Slight

0.5 -1.25m

Rain, snow, sleet etc

Moderate

1.25 – 2.5m

 Winds

Rough

2.5 – 4m

Cyclonic - wind of varying direction

Very Rough

4 – 6m

Veering - changing direction clockwise ie NE to SE
Backing - changing direction anti clockwise ie SE to NE

Wind is defined by the Beaufort Scale:

No.

Description &  Wind Speed

Sea  State

Sail / Power

1

Light airs  1 - 3 knots

Ripples.

Sail - drifting conditions
Power - fast planing conditions

2

Light breeze  4 - 6 knots

Small wavelets.

Sail - full mainsail and large genoa
Power - fast planing conditions

3

Gentle breeze  7 -10 knots

Occasional crests.

Sail - full sail
Power - fast planing conditions

4

Moderate breeze 11-16 knots

Frequent white horses.

Sail - reduce headsail size, maybe reef mainsail
Power - may slow down if wind against tide

5

Fresh breeze 17-21 knots

Moderate waves, many white crests.

Sail - reef mainsail
Power - reduce speed to prevent slamming when going upwind

6

Strong breeze 22-27 knots
Strong wind warning

Large waves, white foam crests.

Sail - reef main and reduce headsail
Power - displacement speed

7

Near gale  28 - 33 knots

4m waves.  Sea heaps up, spray, breaking waves, foam blows in streaks.

Sail - deep reefed main, small jib

Power - displacement speed

8

Gale 34 - 40 knots
Gale warning

Moderately high waves (5.5m), breaking crests. Foam is blown in streaks. 

Sail - deep reefed main, storm jib
Power - displacement speed, head to waves

9

Severe gale 

41 - 47 knots

High waves (7m), spray affects visibility.  Dense streaks of foam along the direction of wind; crests of waves begin to topple and roll over.

Sail - trysail and storm jib, heave to, lie ahull?

Power - displacement speed, head to waves

10

Storm 

48-55 knots

Very high waves (9m) long breaking crests.

Survival conditions
Whatever works! 
Sea anchor?  Drogue? Trail Warps?

11

Violent Storm 53 – 63 knots

11m waves
Sea covered in foam.  Visibility affected.

 

12 - 17

Hurricane  > 64 knots

11m+ waves
The air is filled with foam and spray; sea completely white with driving spray; visibility very seriously affected.

‘Or that which no canvas could withstand’   (Admiral Beaufort)

Posted 3rd August 2011