In METAR, what is indicated by "VRB04KTS"?

The notation "VRB04KTS" in a METAR report indicates variable winds at a speed of 4 knots. The "VRB" prefix specifically denotes that the wind direction is variable, which means it does not consistently blow from a single compass direction but rather shifts between different directions. The "04" indicates the wind speed, which is 4 knots, and "KTS" stands for knots, the unit of measure for wind speed.

This interpretation aligns with standard meteorological practices, where variable winds can occur in various weather conditions and are reported to assist pilots and meteorologists in understanding the air conditions. The presence of both "VRB" and the numerical wind speed provides clear and concise information about the wind conditions at the reporting airport, which is critical for flight operations and safety.