Which of the following denotes intense precipitation in METAR reporting?

The correct designation for intense precipitation in METAR reporting is indicated by the plus sign. In METAR reports, a plus sign before precipitation types signifies moderate to heavy precipitation. This distinction helps pilots and meteorologists quickly assess weather conditions.

The other options do not denote intense precipitation. For instance, a minus sign typically indicates light precipitation, while the letter "X" is not used in METAR to represent precipitation intensity. The letter "u" is also not a recognized code for precipitation intensity in METARs and is instead unrelated to this context. Hence, the emphasis on the plus sign makes it clear that it represents significant precipitation, which is vital for aviation safety and operational planning.