The sudden outburst of radiation, plasma and magnetic field structures from the atmosphere of the Sun causes space weather effects on the Earth. The Coronal Mass Ejection (CME), the Solar Flares, the High Speed Solar Wind streams (HSSWs) emanating from a Coronal Hole (CH), interacting with the slow streams producing intense magnetic field regions called the Co-rotating Interaction Regions (CIRs), are the major sources of disturbances that impact the modern space-based navigational and communication satellite systems. To understand the effect of the solar storms giving rise to geomagnetic storms, this work presents a novel approach to study impacts of strong-to-moderate geomagnetic storms on the ionosphere of the Indian longitude sector during the descending-to-minimum phase of a solar cycle. The study covers locations from beyond the northern crest of the Equatorial Ionization Anomaly (EIA) to the magnetic equator. The Total Electron Content (TEC) derived from the Global Positioning System (GPS), and the Navigation with Indian Constellation (NavIC) is used for analysis. Furthermore, the latest versions of the empirical models: the International Reference Ionosphere (IRI), the IRI extended to-Plasmasphere (IRI-Plas), and the NeQuick are validated over the Indian sector with NavIC and GPS observables during geomagnetically disturbed conditions. The results show that even during the declining phase of a solar cycle, where solar activity is expected to be low, storm-induced electrodynamics causes TEC enhancements of about 50TEC Units (TECU) over the quiet time ionospheric values, thus resulting in degradation of GNSS receiver performance to navigation. This holistic study fills the gap in understanding the ionospheric behavior during disturbed geomagnetic conditions and addresses the need for improvement in the ionospheric models for accurate predictions of the ionosphere over the geosensitive Indian subcontinent.