Module 13 - Meteorology
Weatherfax and Weather Satellite Information
What you will learn
Distinguish analysis, forecast and observed imagery, check issue and valid times, and use each product as independent corroboration rather than a replacement forecast.
Weatherfax can deliver synoptic products; satellite imagery shows observed cloud. Both add evidence, but neither directly supplies every surface condition at the yacht.
A weatherfax product may be an analysis or forecast chart delivered by radio or downloaded electronically. Check the product name, area, source, issue time and valid time before using it. Delivery method does not prove that the chart is current.
Visible and infrared satellite images can show cloud bands, convective development and low-cloud patterns. They are observations at an image time, not a direct readout of surface wind, barometric pressure, wave height or visibility beneath every cloud layer.
Compare imagery and charts with the current Shipping or Inshore Waters Forecast, warnings, NAVTEX/MSI and onboard observations. Agreement can strengthen a model; disagreement is a reason to seek a newer or different authoritative source and retain margin.
Classify the product before trusting it
A downloaded surface chart is valid at 1200, a satellite image is stamped 0930, and the yacht is planning a 1500 headland passage.
1. Name each product
The chart is a model for 1200; the image is an observation at 0930.
2. Check relevance
Compare both times and areas with the 1500 route.
3. Look for agreement
See whether cloud bands and system positions support the current marine forecast.
4. Update
Obtain the latest forecast, warnings and observations before the exposed leg.
Sense check: A cloud-free satellite pixel does not prove good surface visibility, and a forecast chart valid at noon is not a live 1500 observation.
Common mistake or limitation
- Using ‘weatherfax’ as though it describes one fixed product rather than a delivery route for analyses and forecasts.
- Treating satellite cloud imagery as a direct surface-wind or visibility map.
- Ignoring issue and valid times because the file was downloaded recently.
Recap
- Identify product, source, issue time, valid time and area.
- Satellite imagery is observed cloud evidence, not every surface variable.
- Use charts and imagery to corroborate current official marine information and onboard observations.
Optional quick check
Section 12 of 15
What is the first check on a downloaded weather chart?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying Meteorology
This public lesson is part of Revision Module 13. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.