  We report observations of a stellar occultation by Pluto on 2019 July 17. A
single-chord high-speed (time resolution $= 2\,$s) photometry dataset was
obtained with a CMOS camera mounted on the Tohoku University 60 cm telescope
(Haleakala, Hawaii). The occultation light curve is satisfactorily fitted to an
existing Pluto's atmospheric model. We find the lowest pressure value at a
reference radius of $r = 1215~{\rm km}$ among those reported after 2012,
indicating a possible rapid (approximately $21^{+4}_{-5} \%$ of the previous
value) pressure drop between 2016 (the latest reported estimate) and 2019.
However, this drop is detected at a $2.4\sigma$ level only and still requires
confirmation from future observations. If real, this trend is opposite to the
monotonic increase of Pluto's atmospheric pressure reported by previous
studies. The observed decrease trend is possibly caused by ongoing ${\rm N_2}$
condensation processes in the Sputnik Planitia glacier associated with an
orbitally driven decline of solar insolation, as predicted by previous
theoretical models. However, the observed amplitude of the pressure decrease is
larger than the model predictions.
