The overall goal of the fixed-station transects was to establish simultaneous temperature measurements to assess the timing of the peak diurnal and seasonal UHI and the influence of land-cover on temperature. The fixed-station measurements consisted of a network of ten automated Series-8 HOBO Pro-Temp Data Loggers (Onset Corporation, Pocasset, MA), calibrated to each other and to the ASOS temperature sensor at San Juan airport, to record temperature measurements near different types of land-cover ranging from the center of San Juan to barely developed regions 20 km to the east of the city center. We attached the HOBO sensors to telephone poles about 3 meters above the ground surface. The sensors were all placed within 50 meters of sea level, so elevation should not influence our results. Air temperature measurements were logged automatically at 5 minute intervals, and then aggregated into hourly averages for data analysis. We did not measure humidity because temperature was the primary focus of this study and because the atmospheric controls on humidity are varied and different than that for temperature. The HOBO temperature loggers had internal sensors that, according to the manufacturer's specifications, have a 90% response time in still air of up to 35 minutes and an accuracy of ±0.2°C over the range of temperatures measured in Puerto Rico. The error would be larger if radiation errors were present, but we placed the loggers in naturally ventilated radiation shields provided by Onset specifically to reduce radiation-caused error. Temperature measurements collected during calibration exercises performed in a laboratory resulted in an average standard deviation among all sensors of 0.11°C.