With the help of a Lagrangian moisture source diagnostic, linkages between stable isotope measurements in water vapor in Rehovot (Israel), with typical sampling times of 8 hours, and the meteorological conditions in the evaporation regions are established. These linkages can be formulated in quantitative terms, and are also quantitatively comparable with other data from isotope measurements over the ocean and with simple theoretical calculations. On the one hand, a strong negative correlation (r = −0.82) between relative humidity with respect to sea surface temperature in the source regions and measured deuterium excess (d) is found, corroborating results from isotope global circulation model simulations. This relationship can also be applied to model d in a larger region, as shown for a sample case. On the other hand, sea surface temperature in the evaporation regions does not correlate well (r = −0.21) with measured d. This finding contradicts results from other models. Although requiring confirmation by isotope data from different regions, this weak correlation is potentially of major importance for the interpretation of deuterium excess measured in ice cores, which has been used to reconstruct moisture source temperatures for past climates.