Average monthly precipitation and temperature from 90 weather stations of the U.S. Weather Service were used to compute the soil moisture and temperature regimes using the Newhall Simulation Model program version 1.0. This model was validated with soil moisture and temperature data of five weather stations of the USDA-Natural Resources Conservation Service. The study confirms the existence of soils with an aridic moisture regime in Puerto Rico. The Newhall Simulation Model identified an area of 25,450 ha with an aridic moisture regime along the south coast and on Mona Island. This is the first official recognition of an aridic moisture regime in Puerto Rico. An area with ustic soil moisture regime in the northwest corner of the island was also identified. This area is currently recognized as an udic moisture regime. The isomesic temperature regime, previously identified at the Caribbean National Forest was not identified by the Newhall Simulation Model. The isothermic temperature regime previously identified in areas above 600 m over sea level, was identified by the model in areas above 900 m under a udic moisture regime and above 750 m under perudic moisture regime. As a result of these changes in the soil climate regimes, 20 soils series with an aridic soil moisture regime have been identified. Sixteen of these series have been classified as Aridisols.