Photos and videos shared on social media sites depicted long lines at stores as residents stocked up on water and non-perishable items.
Gabriel Rivera-Cruz, a resident of San Juan, went to Costco on Thursday night with his family. He said he wanted to get supplies "before people flooded the stores" to buy water and canned food, but the lines were already long.
"I was surprised to see the long lines," Rivera-Cruz told CNN. "I think the memories from (last year's) hurricanes are so fresh that we have a clear idea of the effects and which items can be scarce or hard to find.
"Most people I know are aware that this storm doesn't seem to be a second Maria, but is simply a wake-up call that the hurricane season is here and we are still extremely vulnerable.”