  Analyses of Galactic late O dwarfs (O8-O9.5V) raised the `weak wind problem':
spectroscopic mass loss rates ($\dot{M}$) are up to two orders of magnitude
lower than the theoretical values. We investigated the stellar and wind
properties of Galactic late O giants (O8-O9.5III). We performed a spectroscopic
analysis of nine O8-O9.5III stars in the ultraviolet (UV) and optical regions
using the model atmosphere code CMFGEN. From the UV region, we found $\dot{M}$
$\sim$ $10^{-8}-10^{-9}$ $\mathrm{M_\odot}$ $\mathrm{yr^{-1}}$ overall. This is
lower by $\sim 0.9 - 2.3$ dex than the predicted values based on the (global)
conservation of energy in the wind. The mass-loss rates predicted from first
principles, based on the moving reversing layer theory, agree better with our
findings, but it fails to match the spectroscopic $\dot{M}$ for the most
luminous OB stars. The region of $\log(L_\star/L_\odot) \sim 5.2$ is critical
for both sets of predictions in comparison with the spectroscopic mass-loss
rates. CMFGEN models with the predicted $\dot{M}$ (the former one) fail to
reproduce the UV wind lines for all the stars of our sample. We reproduce the
observed H$\alpha$ profiles of four objects with our $\dot{M}$ derived from the
UV. Hence, low $\dot{M}$ values (weak winds) are favored to fit the
observations (UV + optical), but discrepancies between the UV and H$\alpha$
diagnostics remain for some objects. Our results indicate weak winds beyond the
O8-9.5V class, since the region of $\log(L_\star/L_\odot) \sim 5.2$ is indeed
critical to the weak wind phenomenon. Since O8-O9.5III stars are more evolved
than O8-9.5V, evolutionary effects do not seem to play a role in the onset of
the weak wind phenomenon. These findings support that the $\dot{M}$ (for low
luminosity O stars) in use in the majority of modern stellar evolution codes
must be severely overestimated up to the end of the H-burning phase.
