NICER Observations of the 2018 Outburst of XTE J1810-197

We present the earliest available soft X-ray observations of XTE J1810-197, the prototypical transient magnetar, obtained 75-84 days after its 2018 outburst with the Neutron Star Interior Composition Explorer. Using a series of observations covering eight days we find that its decreasing X-ray flux is well described by either a blackbody plus power law or a two-blackbody spectral model. The 2-10 keV flux of the source varied from (1.206 ± 0.007) × 10^-10 to (1.125+/- 0.004)× {10}^-10 {erg} {{{s}}}^-1 {cm}}^-2, a decrease of about 7% within our observations and 44% from that measured 7-14 days after the outburst with NuSTAR. We confirm that the pulsed fraction and spin pulse phase of the neutron star are energy dependent up to at least 8 keV. Phase-resolved spectroscopy of the pulsar suggests magnetospheric variations relative to the line of sight.