The ratio or difference between the strongest gusts and the average (or lull) wind speed, indicating how variable and gusty the wind conditions are.
Gust factor is one of the most important but overlooked aspects of wind conditions for watersports. A forecast of 20 knots average with gusts to 30 knots has a gust factor of 1.5x — that's a very gusty day. The same 20-knot average with gusts to only 23 knots is much steadier and more pleasant.
High gust factors make gear selection difficult: do you rig for the lulls (and be overpowered in gusts) or for the gusts (and be underpowered in lulls)? Thermal winds tend to have low gust factors because they build gradually and blow consistently. Frontal and storm-driven winds often have high gust factors with violent gusts and deep lulls. Trade winds are usually somewhere in between.
Gusty conditions are particularly dangerous for kitesurfers because a sudden gust can overpower the kite and loft the rider uncontrollably. Experienced riders check not just wind speed but gust and lull readings before choosing gear.
Example usage
"The gust factor was insane today — 15 knots in the lulls, 32 in the gusts. Couldn't pick a kite size that worked for both."
Watersports Tracker records your speed, distance, route, and more — for 24+ sports.