From this Washington Post article:
"Basically, Hurricane Irma is so strong and its pressure is so low, it’s sucking water from its surroundings into the core of the storm.
This isn’t the sign of a tsunami. The water will return to Long Island (island in the Bahamas) and it probably won’t rush back with any great force. It will probably be back by Sunday afternoon."
- Angela Fritz, Meteorologist
This particular instance is not the sign of a tsunami. Water retreating into the ocean after a shock wave caused by an earthquake would be a sign of a tsunami.