Narrative:

The AWOS at ZZZ was out of service and dispatch was providing hourly weather reports from an observer in ZZZ. The winds favored runway xx; and we were shooting the rnp xx approach. The previous hourly had a 500 foot broken layer; which would have made the approach iffy; since minimums for that approach are 651 feet AGL. When we called ZZZ to get an update from the weather observer; we were told that the 500 foot layer was gone; and only the 2000 foot overcast remained. All was normal during the approach until we broke out into VMC conditions - the GPWS started giving terrain warnings; and we could see that we were low. The instruments all showed us on profile. We were VMC and had the terrain and runway in sight; so we completed the landing; only to see that our altimeters; set to 29.71 from the hourly; were reading about 450 feet. ZZZ is at 20 feet. When I went in to the office at ZZZ where the weather observation altimeters are located; they were; indeed; set at 29.71; but showed the same readings as the aircraft altimeters.it turns out that the weather observer was new; and although she had a certificate; she had only passed a written test; but had not been given any training. I had to show her how to set the altimeters to field elevation; check them for differences; and then read the altimeter setting; which turned out to be 29.25' at the time. There is another certified weather observer on the island who is supposed to have had training; but she was busy with another job; and was not at the airport.I recommend that ZZZ flights be cancelled when the AWOS is out of service; unless there is a properly certified and trained! Weather observer available.

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Original NASA ASRS Text

Title: During an RNAV approach; an air carrier flight crew experiences GPWS terrain warnings as the aircraft descends below 2000 feet in VMC. With the field in sight the approach is continued to landing. The AWOS was out of service and the altimeter setting came from the hourly weather provided by an observer. The observer had not been properly trained and the actual altimeter setting was 29.25 instead of 29.71; a 460 foot difference.

Narrative: The AWOS at ZZZ was out of service and Dispatch was providing hourly weather reports from an observer in ZZZ. The winds favored runway XX; and we were shooting the RNP XX approach. The previous hourly had a 500 foot broken layer; which would have made the approach iffy; since minimums for that approach are 651 feet AGL. When we called ZZZ to get an update from the weather observer; we were told that the 500 foot layer was gone; and only the 2000 foot overcast remained. All was normal during the approach until we broke out into VMC conditions - the GPWS started giving Terrain warnings; and we could see that we were low. The instruments all showed us on profile. We were VMC and had the terrain and runway in sight; so we completed the landing; only to see that our altimeters; set to 29.71 from the hourly; were reading about 450 feet. ZZZ is at 20 feet. When I went in to the office at ZZZ where the weather observation altimeters are located; they were; indeed; set at 29.71; but showed the same readings as the aircraft altimeters.It turns out that the weather observer was new; and although she had a certificate; she had only passed a written test; but had not been given any training. I had to show her how to set the altimeters to field elevation; check them for differences; and then read the altimeter setting; which turned out to be 29.25' at the time. There is another certified weather observer on the island who is supposed to have had training; but she was busy with another job; and was not at the airport.I recommend that ZZZ flights be cancelled when the AWOS is out of service; unless there is a properly certified and TRAINED! weather observer available.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.