From the National Weather Service:

Isaias has strengthened overnight into a hurricane.  Attached is our latest briefing.  Our confidence has increased that we will be impacted by Isaias, but our confidence still remains low especially with regards to intensity and timing. For timing, please refer to the earliest onset of tropical storm force winds as a reasonable worse case scenario in terms of your planning.  The most likely time for the arrival of tropical storm force winds is still sometime during the day Monday.