Are the longitude and latitude values to be interpreted as centroids of each grid cell? That is, the tuples constructed from every combination of (longitude, latitude) will give the centroid of each grid cell in the geographic area of interest that I downloaded?
"Regarding to your question on the coordinate conventions, could you please take a look on the NLDAS FAQ https://ldas.gsfc.nasa.gov/faq/nldas (search for Q. What geographic coordinate system was used to generate the NLDAS grid?).
As described in this answer and the links within it, the center of the grid box is the exact lat/lon given. The lower-left corner point is exactly 25.0625 N and 124.9375 W; each grid box going north and east is 0.125 degrees away from this point."