That most recent time was just a year ago, when Hurricanes Irma, Jose and Maria all reached hurricane status at the same time, and the aftermath of both Irma and Maria are still being felt in the Caribbean and Florida.
The NHC's 11 a.m. advisory says that additional strengthening is expected for Hurricane Isaac is expected over the next day or two.
By noon EDT on Monday, Florence had top sustained winds of 130 miles per hour. "On the forecast track, Isaac should move across the Lesser Antilles and into the eastern Caribbean Sea on Thursday", the NHC said.
There is an increasing risk of storm surge at the coast and damaging hurricane-force winds in the Carolinas.
Helene has sustained winds of 65 miles per hour and is moving west at 13 miles per hour.
South Carolina Governor Henry McMaster said Hurricane Florence is gaining strength and could potentially hit as a Category 4 hurricane.
It's too early to know the exact path of Florence, but forecasters said it could blow ashore by Thursday in the Carolinas and southern Virginia, a stretch of the U.S. East Coast that experts have identified as the most vulnerable to rising sea levels due to climate change.
Hurricane Helene is in the far eastern Atlantic Ocean and not expected to be near any land. "But on rare occasions, the steering patterns can line up such that a storm slips into a dead zone between troughs and ridges".
Large swells could be generated and cause damage in some parts of the state, which survived brushes with hurricanes Hector and Lane in recent weeks.
At 11 p.m., the center of the storm was located about 535 miles west of the southernmost Cabo Verde Islands.
Southeastern North Carolina remains in the middle of the storm's "cone of uncertainty", with the cone extending from roughly Hilton Head, S.C., in the south to the Chesapeake Bay in the north. Odds are high that this storm avoids any future landfall.
President Donald Trump declared states of emergency for North and SC, facilitating federal help, and canceled campaign events Thursday and Friday, citing the storm.
Isaac was expected to strengthen to a hurricane by Wednesday morning, but will then likely weaken back to a tropical storm by Wednesday night.
The University of North Carolina at Wilmington, near the shore, canceled its upcoming alumni weekend and all classes starting at noon Monday, encouraging its students to leave campus for a safer location.