An earthquake has happened in the Nankai Trough every 100-150 years in the past. Roughly 70 years have passed since the last one in 1946, and there is a 70% chance that a large earthquake of magnitude 8-9 will happen in the next 30 years.
The 2011 Tohoku Earthquake and Tsunami surpassed all previous expectations and caused massive damage. Learning from this, we have built our expectations of the Nankai Trough Earthquake and Tsunami on a scientifically conceivable disaster of the largest scale. The frequency of such a large earthquake is very low, and nobody knows whether it will be on the largest scale, but should it be a large scale earthquake/ disaster, it would cause massive damage. It is predicted that an earthquake in Kobe City would be 6 Lower to 6 Upper on the Seismic Intensity Scale, and the water level of a tsunami at high tide is predicted to be 3.9 metres.
Reference: Disaster prevention living guide, Kobe City Homepage "Tsunami Predictions following a Nankai Trough Earthquake and Preparations for a Tsunami" (Japanese only)
According to large scale earthquake/tsunami predictions, in the worst case scenario flooding is expected along the coast from Higashi Nada ward in the east to Suma Ward in the west of Kobe. There are some areas in Higashi Nada, Chuo and Hyogo Ward where the water level will reach over 2.0m.
However, it will take a minimum of 83 minutes to reach the city (Tarumi Ward), and 90 minutes to reach Chuo Ward. For example, if you were to walk from Meriken Park on the coast up to near the JR Line, which is outside of the anticipated flooding area, it would take around 15 minutes. There is time to evacuate calmly. By checking whether the place you are going to visit is within the flooding zone before coming to Kobe, you will be able to evacuate calmly and without panicking if an earthquake happens and a tsunami warning/alert is issued.
Reference: Kobe City Homepage "Tsunami Predictions following a Nankai Trough Earthquake and Preparations for a Tsunami" (Japanese only)