Which TAF abbreviation represents heavy rain?

The abbreviation that represents heavy rain in TAF (Terminal Aerodrome Forecasts) is actually "RA." The code "RA" specifically indicates rain, and when it is used in the context of TAFs to denote significant precipitation, it is understood that heavy rain might be expected.

The other abbreviations have distinct meanings: "SH" signifies showers, which may not always indicate heavy rain, as showers can be light to moderate. "HR" is not an official meteorological abbreviation widely recognized within the TAF or METAR context for heavy rain; rather, it typically could mislead or confuse as it's not standardized. "SR" is used for snow, denoting snow conditions rather than rainfall.

Understanding these abbreviations is crucial for interpreting terminal aerodrome forecasts accurately, as they play a vital role in aviation safety and planning.