The word "in-surge" refers to a sudden and powerful rush of something. Here are some synonyms that can be used in place of "in-surge": influx, surge, rush, flood, deluge, stream, inundation, flow, avalanche, spate, outpouring, blitz, onslaught, charge, attack, raid, assault, hurricane, tempest, tornado, cyclone. These synonyms can be interchangeably used in contexts where an increase in activity or intensity is implied, such as in the case of a sudden increase in the number of customers at a store, a sudden surge in demand for a product, or in the context of a sudden and powerful emotion like anger or excitement.