Offshore weather routing is part science, part craft, and entirely consequential. These guides cover the tools and skills that actually matter at sea: understanding the model data behind the forecast, identifying genuine weather windows, choosing and using routing software, and reading the signs that distinguish a squall from something worse. Each article is written for sailors who are past the basics and preparing for passages where the forecast is all you have.
GRIB Files Explained: The Offshore Sailor's Guide to Model Data
What GRIB format actually is, the GFS vs. ECMWF model hierarchy, ensemble vs. deterministic runs, the variables that matter for sailors, and how to manage file size over satellite comms.
- GFS free vs. ECMWF premium
- Ensemble probability spreads
- File size management for Iridium
Finding and Using Weather Windows
The 72-hour reliable rule, frontal system identification, high-pressure windows, seasonal passage timing for the North Atlantic and Southern Ocean, and how to spot a false window before it costs you.
- 72-hour vs. 5-7 day reliability
- Cold front vs. warm front behaviour
- North Atlantic May–June window
Routing Software Compared: From Free to Professional
PredictWind, Expedition, Weather4D, LuckGrib, Windy, and browser-based tools — how isochrone routing works, when to hire a professional router, and what each tier actually costs.
- PredictWind offshore gold standard
- How isochrone routing works
- Free tools vs. $500+ pro routing
Reading Storm and Squall Forecasts Offshore
Tropical cyclone tracking, the NHC cone of uncertainty, ASCAT satellite wind data, squall identification in GRIB, the 4-hour warning signs at sea, and barometric pressure trends that signal heavy weather.
- NHC 5-day cone misread risks
- ASCAT measured vs. model winds
- 6 hPa/3 hrs = heavy weather imminent
About These Guides
These are editorial resources for offshore passage planning. Atmospheric models, software subscriptions, and routing services change frequently — always verify current pricing, model availability, and forecast reliability with current sources. For ocean crossings, consider supplementing self-routing with a professional meteorologist. See also: Planning Your First Ocean Crossing and the marina directory for staging ports and provisioning stops.