Gili Marine Index: Sea Conditions Before You Cross
Understanding what the sea is doing before you travel makes the difference between a smooth crossing and an uncomfortable one. The Gili Marine Index below updates every 30 minutes with live conditions for the Bali to Lombok to Gili crossing. Here is what the numbers mean and how to use them.
What Is Swell
Swell is the height and rhythm of waves moving across open water, separate from local wind chop on the surface. A boat can handle a longer, gentler swell far more comfortably than the same wave height arriving in short, sharp intervals. When you check the Gili Marine Index, swell height tells you roughly how much the boat will rise and fall, while swell period, the gap between waves, tells you how smooth or jarring that motion will feel. A longer period at the same height is a noticeably easier ride.
What Is Wind
Wind affects the crossing differently than swell does. Strong wind against the direction of travel creates chop on top of the existing swell, making the surface choppier and less predictable even when the underlying swell is moderate. Wind direction relative to your route matters as much as wind speed, a crossing directly into a headwind feels rougher than the same wind speed from behind or the side.
What Is Considered Rough
There is no single number that defines "rough" for every traveller, tolerance varies a lot between people, which is why the Gili Marine Index gives you a plain-language rating alongside the raw numbers rather than just swell height and wind speed on their own. A green rating means calm conditions, small, well-spaced swell and light wind, the kind of morning where most passengers barely notice the motion. Amber means moderate conditions, larger or closer-together swell, occasional spray over the bow, and enough movement that anyone prone to seasickness will feel it. Red means rough conditions, where operators may adjust routes, delay departures, or in some cases suspend crossings entirely until conditions ease. If the Index is showing amber or red for your travel day, it is worth checking directly with your operator before you travel.
Is Today Safe for Children
Operators generally continue running in calm to moderate conditions, and children cross safely on these routes every day. The main considerations are comfort rather than safety, smaller children can find prolonged rougher motion more distressing than adults do, and seasickness affects children more noticeably. If the Gili Marine Index shows rougher conditions on your travel day, a morning departure will usually give a smoother crossing than an afternoon one, and it is worth discussing with your operator whether a larger, more stable vessel is available if that matters for your family.
Morning vs Afternoon Crossings
Morning crossings are consistently calmer across this route. Wind tends to build through the day, so a departure before mid-morning generally means less chop than the same route in the afternoon, even on days with otherwise similar swell. If you have a choice of departure time and are at all concerned about the crossing, morning is the safer default.
Best Time of Year to Cross
Dry season, roughly May to October, brings the calmest and most consistent sea conditions for this crossing, with visibility and comfort both at their best. Wet season, November to April, can still offer plenty of calm days, but conditions are less predictable, afternoon weather in particular. Shoulder months, May to June and September to October, often give a good balance of calm seas without the peak season crowds. Whatever time of year you travel, the Gili Marine Index shows a five-day outlook alongside current conditions, so if you are planning a crossing in the next few days, check the forecast strip rather than relying on the seasonal averages alone.