Weather Manual for Cruisers

Many years of combined knowledge, recreational and commercial sailing the world.


Weather – we can’t avoid it.

Good or bad it’s always with us but with study and observation we can better prepare and, at times, choose the conditions we’d like to tackle.

Understanding Weather the mariner's guide

(For more details and full contents, scroll down: includes southern hemisphere/Australian conditions)

It can be a complex subject, so we have provided the basic study of weather from our international commercial and recreational, and teaching experience. These are notes and tips for you to consider during passage planning and when underway; across vast oceans for weeks on end or a day sail across a harbour.

land breeze
Land Breeze

We’ve incorporated over forty-years combined knowledge while sailing the world. We’ve sorted through the technical aspects, simplified them, and included what we feel is important to those wandering the oceans and coastlines on boats.

what is weather

It’s a fascinating subject and we hope this helps you better understand that weather forecast adjustments are just one of the many hats mariners wear. Weather forecasts are never going to be perfect, it is our responsibility to interpret, adjust, and prepare.


Introduction.. 1

Acknowledgements. 1

A Little History. 2

Technology and Advancement. 2

The Atmosphere. 3

What is Weather?. 4

Weather Terms. 4

Atmospheric Pressure / Air Pressure. 4

Barometer. 5

Diurnal Variation.. 5

Isobar. 6

Relative Humidity. 6

Backing and Veering.. 6

Trade Winds. 6

Ocean Currents. 7

Clouds. 8

Cloud Classification.. 8

Terminology. 9

High Cloud.. 9

Cirrus (Ci) 9

Cirrostratus (Cs) 10

Cirrocumulus (Cc) 11

Middle Cloud.. 11

Altostratus (As) 11

Altocumulus (Ac) 12

Low Cloud.. 12

Stratus (St) 13

Cumulus (Cu) 13

Stratocumulus (Sc) 14

Towering Cumulus (Tcu) 14

Cumulonimbus (Cb) 16

Wind.. 18

What is Wind?. 19

Cycles of Air. 21

Air Pressure and Wind.. 22

Bringing It Together – Weather Systems and Events. 24

Ridge. 24

Ridge – What does this mean to the sailor?. 25

Depression or Low… 25

Trough.. 25

Occluded Fronts. 31

Jet Streams. 31

Jet Streams – What They Mean to Us. 32

Forecasting Frontal Weather. 33

East Coast Lows. 34

Katabatic Winds. 34

Local Weather Patterns. 34

Sea Breeze. 35

Land Breeze. 35

The Effect of Land and Sea-Breezes on Gradient Wind – What It Means to Us. 36

Equatorial Trough/Intertropical Convergence Zone (ITCZ) 36

El Niño La Niña.. 37

The Indian Ocean Dipole (IOD) 38

Thunderstorms. 38

Developing Thunderstorms. 38

Tornados and Waterspouts. 38

Wind – Apparent & True. 39

Wind Vectors. 39

Tropical Revolving Storms (TRS) or Tropical Cyclones. 40

Development of a Cyclone. 41

Warning Signs. 41

Three Stages of a Cyclone. 41

Tracking a Cyclone. 42

Australian areas. 42

Cyclone Paths. 42

Non-navigable and Navigable Semicircle. 42

To Evade a Cyclone. 43

Angle of Indraft. 44

Storm Surge. 45

Measuring the Strength of Tropical Revolving Storms, Cyclones, Hurricanes & Typhoons. 45

Saffir-Simpson Scale. 45

Australian Scale. 45

Cyclone Warning System.. 46

Forecasting Weather.. 46

Weather Forecasts. 46

When to Listen to Forecasts. 46

Sources of Weather Information.. 46

VHF Broadcasts by State and Territory Authorities. 47

Charleville (VMC) Broadcast Schedule. 47

WeatherFax. 47

Reading a Synoptic Chart.. 48

Synoptic Charts – Mean Sea Level Pressure Analysis (MSLP) 48

Rain or Fine?. 52

How Strong Will the Winds Be?. 53

Line Squalls. 55

Col. 56

A Case Study. 56

Buys Ballot’s Law.. 58

Forecasting Exercise. 58


BOM Tropical cyclone services. 59

Tropical cyclone seasonal outlook.. 59

Tropical cyclone outlook. 59

Tropical cyclone information bulletin.. 59

Tropical cyclone watch.. 59

Tropical cyclone warning.. 59

Technical bulletin.. 59

Tropical cyclone forecast track map. 59

Tropical cyclone forecast track maps: GIS Compatible Format. 60

Marine warnings. 60

HF Radio Stations from BOM… 61

Notes. 62

Notes. 64

Telephone Weather Services Directory. 64


APPENDIX 1: Cyclone Preparation.. 68

Anchoring or in a Marina: 68

When a Cyclone Warning is Issued.. 68

Personal Preparation.. 69

Detailed Preparation.. 69

Safety. 70

Storm Surge. 70


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