  With theoretical constraints such as perturbative unitarity and vacuum
stability conditions and updated experimental data of Higgs measurements and
direct searches for exotic scalars at the LHC, we perform an updated scan of
the allowed parameter space of the Georgi-Machacek (GM) model. With the refined
global fit, we examine the allowed parameter space for inducing strong
first-order electroweak phase transitions (EWPTs) and find only the one-step
phase transition is phenomenologically viable. Based upon the result, we study
the associated gravitational wave (GW) signals and find most of which can be
detected by several proposed experiments. We also make predictions on processes
that may serve as promising probes to the GM model in the near future at the
LHC, including the di-Higgs productions and several exotic scalar production
channels.
