If you're sailing from Bali to Nusa Penida or the Gili Islands, first check the "marine picture" along the boat's route.
Weather conditions, combined with the human factor, play a significant role in the majority of shipwrecks. Sometimes, the only right decision is to cancel the trip while still onshore.
How to Decide If It’s Safe to Sail Today
— Open Windy.com (a convenient layered map). Find your route.
Routes on the map are almost in a straight line: zoom in, place the cursor along the route at several points — near the coast and "in the ocean," to see how conditions change.
Recommended Limits for Speedboats
The key is three layers: 'Wind,' 'Waves,' and 'Visibility.' Check the selected time on the timeline at the bottom:
— Wind: above 15 m/s — a reason to decline.
— Waves: over 1 meter — the trip becomes risky.
— Visibility: less than 1 nautical mile — do not sail.
For ferries and vessels of other classes, acceptable values may differ. Guidance for ferries:
— Large ferries: conditionally safe up to ~25 m/s and ~3 meters; at 3–4 meters and/or visibility <1 mile — better not go out.
— Medium ferries: up to ~20 m/s and ~2 meters; at 2–3 meters and/or visibility <1–0.5 miles — risky.
— Small/tourist ferries: up to ~17 m/s and ~1 meter; at 1–2 meters and/or visibility <0.5 miles — decline. (1 nautical mile = 1852 meters).
How to Check Conditions on the Map
— Place the cursor on the route: the point shows all the parameters right there.
— Move the orange time slider below — see if the waves or wind "spike" at your departure time.
— Select the needed layer (e.g., "Waves") — find it in the layers menu (red circle on the right).
— Found the point — press the orange button "Forecast for this point" to see a detailed table of the selected indicator by hours.
If wind and waves are confidently below the specified thresholds and visibility is normal — book your tickets. If close to the threshold or worse — postpone the trip.
Other Important Weather Factors
Rain and Thunderstorm
— Check the "Rain, Thunderstorm" layer. Rain itself is not always critical, but heavy rain and thunderstorm activity are often accompanied by gusts and sharp "steps" in waves. If active thunderstorm cells are present at your hour, it's wiser to wait.
Wind Gusts
— In the "Gusts" layer, you can see if the speed "shoots" above average briefly. For a small boat, strong gusts are almost always discomfort and risk.
Surf at the Boarding Point
— In Sanur and Kusamba, the coastal wave can be higher than in open water. Even with a "normal" overall wave, boarding/disembarking can become dangerous. Check the "Waves" layer right at the departure point.
Current
— In the Lombok Strait (to the Gili Islands), the current is noticeable. Look at the current map as an additional guide: a strong countercurrent with moderate waves will result in a long and "hard" crossing.
Temperature and Precipitation
— On long crossings, it is useful to check the temperature front and precipitation strip.
Alternative Transport Options
— Windy — a basic "combine" with visual layers. Convenient for a visual assessment of the route by points and time.
— Windfinder — shows wind and waves well by spots; notifications and quick "cards" by locations are convenient.
— PredictWind — accurate marine models and routing (in the paid version) for those going longer and wanting to compare multiple forecast models.
Useful Tips Often Overlooked
— Compare several models/services: if two out of three show an increase in waves at your hour — that's a signal.
— Look not only at "now," but also +3–6 hours from departure: conditions on the return journey may change.
— Follow the carrier's messages: mass flight cancellations are an indicator of deterioration, especially in narrow parts of the route (surf at the pier, wave "steps" in the strait, etc.).
— Local factors affect ocean weather: coastal configuration, reef, approach direction — so always check several points along the route, not just one.
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