MPH

Knots

WMO

Classification

Appearance of Wind on Sea

Appearance of Wind on Land

Dinghy Sailors Interpretation at

Chipstead

0

< 1

< 1

Calm

Surface smooth and mirror-like

Calm, smoke rises vertically

Sailors stand around drinking tea.

1

1-2

1-3

Light Air

Scaly ripples, no foam crests

Smoke drift indicates wind.

direction, still wind vanes

Very light and patchy: an Oppie wins the race!

2

4-7

4-6

Light Breeze

Small wavelets, crests glassy, no breaking

Wind felt on face, leaves rustle, vanes begin to move

A nice gentle racing wind. 

3

8-12

7-10

Gentle Breeze

Large wavelets, crests begin to break, scattered whitecaps

Leaves and small twigs constantly moving, light flags extended

A decent racing breeze: things are getting lively.

4

13-18

11-16

Moderate Breeze

Small waves 1-4 ft. becoming longer, numerous whitecaps

Dust, leaves, and loose paper lifted; small tree branches move

Very lively, some capsizes. Toppers come to life!

5

19-24

17-21

Fresh Breeze

Moderate waves 4-8 ft taking longer form, many whitecaps, some spray

Small trees in leaf begin to sway

Probably too much wind for novices unless using reefed.

Toppers = Much capsizing. 

6

25-31

22-27

Strong Breeze

Larger waves 8-13 ft, whitecaps common, more spray

Larger tree branches moving, whistling in wires

Many sailors stay ashore and watch the fun

7

32-38

28-33

Near Gale

Water heaps up, waves 13-19 ft, white foam streaks off breakers

Whole trees moving, resistance felt walking against wind

Only a few Lasers go out sailing 

8

39-46

34-40

Gale

Moderately high (18-25 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks

Twigs     breaking      off     trees,

generally, impedes progress

Only for the very experienced and foolhardy….. and they soon regret it!

9

47-54

41-47

Strong Gale

High waves (23-32 ft), water begins to roll, dense streaks of foam, spray may reduce visibility

Slight structural damage occurs, slate blows off roofs

Sailors go and check that their boats and those next to them are well tied down. 

10

55-63

48-55

Storm

Very high waves (29-41 ft) with overhanging crests, water white with densely blown foam, heavy rolling, lowered visibility

Seldom experienced on land, trees broken or uprooted,

“considerable structural damage”

Sailors stay at home 

11

64-72

56-63

Violent Storm

Exceptionally high (37-52 ft) waves, foam patches cover

water, visibility more reduced

Very rarely experienced – widespread damage

Club Committee organise emergency meeting to discuss new clubhouse roof. Boats blown over fences, rescue boats blown ashore.

12

73+

64+

Hurricane

Air filled with foam, waves over 45 ft, water completely white with driving spray, visibility greatly reduced

Very rarely experienced – widespread damage 

Michael Fish was right: 

Fortunately, we don’t get these in the UK.