In a remarkable development, using the measurements of total electron content (TEC) of the ionosphere at 18 different stations across the length and breadth of India (covering the crest and trough of the Equatorial Ionization Anomaly) under GAGAN (GPS Aided Geo Augmented Navigation), a model has been developed which would successfully predict the TEC between 8-30deg. latitude and 60-100deg. longitude zone. In this model, observations at 77deg. longitude zone are considered as reference and the solar zenith/neutral wind control are applied to estimate changes in TEC at different longitude sectors from that at 77deg. longitude emphasizing a first principle based the Parametric Ionospheric Model (PIM). The model has now been modified to include the variabilities in Kp and F10.7 cm flux to represent the impact of geomagnetic storms at low latitude. A case study for the severe geomagnetic storm of August 24, 2005 (Dst -158 nT; Kp ~9) revealed that ISRO-TEC model successfully predicted temporal variations in TEC even at longitudes far away from the reference longitude zone at 77deg. The model is now being used to generate super-truth data for GAGAN certification process. A detailed evaluation of the performance of the model with that developed by Raytheon has shown that SPL developed TEC model to be superior. A comparison of ISRO-TEC model generated TEC with the observed measurements and IRI-2007 Storm model for the storm event of August 24, 2005 at two mid-latitude Indian stations viz., Guwahati (26.2deg. N, 91.7deg. E) and Kolkata (22.6deg. N, 88.4deg. E ) is shown in the figure. Needless to say, the ISRO-TEC model represents the real Indian ionosphere better.