  In this study, we present a new method for forecasting arrival times and
speeds of coronal mass ejections (CMEs) at any location in the inner
heliosphere. This new approach enables the adoption of a highly flexible
geometrical shape for the CME front with an adjustable CME angular width and an
adjustable radius of curvature of its leading edge, i.e. the assumed geometry
is elliptical. Using, as input, STEREO heliospheric imager (HI) observations, a
new elliptic conversion (ElCon) method is introduced and combined with the use
of drag-based model (DBM) fitting to quantify the deceleration or acceleration
experienced by CMEs during propagation. The result is then used as input for
the Ellipse Evolution Model (ElEvo). Together, ElCon, DBM fitting, and ElEvo
form the novel ElEvoHI forecasting utility. To demonstrate the applicability of
ElEvoHI, we forecast the arrival times and speeds of 21 CMEs remotely observed
from STEREO/HI and compare them to in situ arrival times and speeds at 1 AU.
Compared to the commonly used STEREO/HI fitting techniques (Fixed-$\Phi$,
Harmonic Mean, and Self-similar Expansion fitting), ElEvoHI improves the
arrival time forecast by about 2 hours to $\pm 6.5$ hours and the arrival speed
forecast by $\approx 250$ km s$^{-1}$ to $\pm 53$ km s$^{-1}$, depending on the
ellipse aspect ratio assumed. In particular, the remarkable improvement of the
arrival speed prediction is potentially beneficial for predicting geomagnetic
storm strength at Earth.
