  We report on an observationally constrained analytical model, the
INterplanetary Flux ROpe Simulator (INFROS), for predicting the magnetic-field
vectors of coronal mass ejections (CMEs) in the interplanetary medium. The main
architecture of INFROS involves using the near-Sun flux rope properties
obtained from the observational parameters that are evolved through the model
in order to estimate the magnetic field vectors of interplanetary CMEs (ICMEs)
at any heliocentric distance. We have formulated a new approach in INFROS to
incorporate the expanding nature and the time-varying axial magnetic
field-strength of the flux rope during its passage over the spacecraft. As a
proof of concept, we present the case study of an Earth-impacting CME which
occurred on 2013 April 11. Using the near-Sun properties of the CME flux rope,
we have estimated the magnetic vectors of the ICME as intersected by the
spacecraft at 1 AU. The predicted magnetic field profiles of the ICME show good
agreement with those observed by the in-situ spacecraft. Importantly, the
maximum strength (10.5 $\pm$ 2.5 nT) of the southward component of the magnetic
field (Bz) obtained from the model prediction, is in agreement with the
observed value (11 nT). Although our model does not include the prediction of
the ICME plasma parameters, as a first order approximation it shows promising
results in forecasting of Bz in near real time which is critical for predicting
the severity of the associated geomagnetic storms. This could prove to be a
simple space-weather forecasting tool compared to the time-consuming and
computationally expensive MHD models.
