Marine Weather Endorsement (ASA 119)

Prerequisites: None

General Description: Understand and demonstrate the proper use of weather information in planning and adapting navigation during local and passage-making voyages.  Demonstrate the ability to use both the latest technological tools as well as traditional maritime skills to forecast weather conditions.


A Certified Sailor has successfully demonstrated his or her understanding of:

1. Basic Concepts

  • The role of marine weather in your boating plans, particularly wind forecasting
  • The relationship of temperature, precipitation, visibility, wind, and waves and their impact on forecasting
  • Wind terminology and units used in speeds, distances, temperatures and pressures
  • Utilizing data from the Ocean Prediction Center, National Data Buoy Center, and Marine Weather Services Charts

2. Pressure and Wind

  • Pressure and wind, including the flow of wind around highs, lows, ridges and troughs
  • Conversion of apparent wind to true wind
  • Calibration and setting of barometers, both aneroid and digital
  • Pressure distributions and related labeling practices on weather maps
  • Predicting wind speed and direction from isobars on a weather  map

3. Global Winds and Currents

  • The basic properties of the atmosphere and their influence on wind and weather
  • Air mass classifications and vertical stability basics
  • The role of equatorial heating in establishing the doldrums, horse latitudes, trade winds and prevailing westerlies
  • The role the polar front plays in generating low fronts, and how these subsequently cross the mid-latitudes of the globe
  • The origins and behavior of the winds aloft and how they contribute to the development and transport of surface systems around the globe
  • The distribution of ocean currents around the globe and how to predict their values in voyage planning

4. Strong Wind Systems

  • Forecasting conventions and warnings available for strong wind systems
  • The distinctions between lows and fronts, and between tropical and extra-tropical storms
  • Predicting squall behavior
  • Finding and using Quick Scat satellite wind measurements
  • Typical behaviors of tropical depressions, storms, and hurricanes

5. Clouds, Fog, and Sea State

  • The ten basic cloud types and what they can indicate
  • Cloud sequences at frontal passage
  • Fog formation and forecasting
  • Practical distinctions between sea fog and radiation fog and between swells, wind waves and ripple
  • Predicting wave height and speed based on wind speed, duration, and fetch
  • The Beaufort Wind Force scale that relates wind speed to sea state

6. Wind and Terrain

  • Presence and topography of land and how it affects the wind flow over adjacent waters
  • Prominent local winds such as: sea breezes, land breezes, channeling and gap winds, blocking and lifting and downslope winds
  • The interaction between thermal winds and pressure system winds

7. Weather Maps Review

  • The types of weather maps available and how to access them at home and underway
    The process of weather routing, including sequencing of analyses and forecasts to confirm the forecasts
  • Accessing and utilizing GRIB forecasts, taking into account their pros and cons compared to analyzed products prepared by meteorologists
  • Using the 500-mb maps and weather discussions to help evaluate surface forecasts
    Utilizing shipboard observations of wind and pressure to evaluate analyses and the subsequent forecasts

8. Sources of Weather Data

  • The use of both traditional and modern sources of climatic data for planning the time and route of voyages-for inland and coastal voyaging, as well as ocean crossings
  • The latest sources for weather data underway and the wireless options for obtaining it
  • The distinctions and pros and cons of commercial weather services compared to free public services from the National Weather Service
  • The role of professional weather routing services and how they might fit into your voyaging plans

  9. On-board Forecasting and Tactics

  • Proper use of barometer, wind speed, wind direction, clouds, and sea state for shipboard forecasting
  • Gauging the direction of the winds aloft from cirrus cloud patterns
  • Know which weather-related old maritime sayings have some value in forecasting
  • The role of weather routing in improving sailing tactics

10. Southern Hemisphere Weather

  • Which aspects of weather are unique, and which are and are not reversed in the Southern Hemisphere
  • The sources for weather information specific to the Southern Hemisphere