The phrase "in surge" typically refers to a sudden or rapid increase in something, such as a surge in demand for a product or a surge of emotion. There are several synonyms that can be used to convey a similar meaning, including "spike," "burst," "surgeon," "rush," and "flood." These words all suggest a quick and powerful rise in intensity or quantity. Other possible synonyms for "in surge" might include "flurry," "blast," "explosion," and "upsurge." Using one of these alternatives can add variety and nuance to your writing, helping you to express your ideas more clearly and effectively.