The phrase "storm break" refers to a pause or lull in a storm.
Some possible antonyms could be "storm onset" or "storm start". When a storm breaks, there is a relief from the intensity and chaos of the storm. In contrast, when a storm onsets or starts, there is a sudden increase in wind, rain, and turbulence. For example, "Just as they were beginning to hope for a storm break, the storm onset brought renewed fear." Or "The storm start was marked by a sudden drop in temperature and a howling wind."
Another possible antonym could be "storm continuation" or "storm persistence". While a storm break implies a temporary respite, storm continuation means that the storm persists without any let-up. For instance, "They had been waiting for a storm break, but instead, the storm continuation made conditions even more difficult." Or "The storm persistence meant that they had to endure the harsh weather for much longer than expected."
In conclusion, antonyms for "storm break" focus on the beginning or continuation of a storm rather than a pause in its fury.