WAAS Outages
This airport if the first one that I’ve run across that has this symbol. It it located in the Florida Keys, which probably explains why it may be outside the reach of WAAS.
NOTE: The W symbol indicates outages of the WAAS vertical guidance may occur daily due to initial system limitations. WAAS NOTAMS for vertical outages are not provided for this approach. Use LNAV minima for flight planning at these locations, whether as a destination or alternate. For flight operations at these locations, when the WAAS avionics indicate that LNAV/VNAV or LPV service is available, then vertical guidance may be used to complete the approach using the displayed level of service. Should an outage occur during the procedure, reversion to LNAV minima may be required.
As the WAAS coverage is expanded, the W will be removed.
From the AIM 1−1−18. Wide Area Augmentation System (WAAS)
7. When the approach chart is annotated with the symbol, W site−specific WAAS MAY NOT BE AVBL NOTAMs or Air Traffic advisories are not provided for outages in WAAS LNAV/VNAV and LPV vertical service. Vertical outages may occur daily at these locations due to being close to the edge of WAAS system coverage. Use LNAV or circling minima for flight planning at these locations, whether as a destination or alternate. For flight operations at these locations, when the WAAS avionics indicate that LNAV/VNAV or LPV service is available, then the vertical guidance may be used to complete the approach using the displayed level of service. Should an outage occur during the procedure, reversion to LNAV minima may be required.
Update: 2021-10-04 Neither GPS approach at this airport has the W symbol.