8PM Thursday Eve - eye parallel to Palm Beach - within 60 miles of shore. That's just 30 hours from now, and expected to be a low Category 4 storm.
The motion is forecast to bring Matthew to the coast overnight Thursday, then ride somewhere between the coast and I-95 for the next 200 miles.
That will make a really bad Thurs. night for the area between PB and Melbourne as this thing crawls up the coast...that's only forecasting a 10 mph forward speed.
That's a long time on target with hurricane force winds or better for probably 10 hours at any point along the coast from about Jupiter to Daytona as the storm passes.
8AM Friday Morning (42 hours away) - eye near Cocoa/Cocoa Beach.
8PM Friday Evening (54 hours) - eye near St. Augustine/JAX Beach, probably over water.
Storm surge: The surge will be ahead of the eye, and though I've seen suggestions of 3-5 feet, that frankly sounds light to me for a cat 4 storm.
This map for the Jacksonville area suggests something close to 14 feet of storm surge for a cat. 3 storm, though it does not give any indication about the angle of storm arrival, speed of motion, or anything else helpful to decipher the methodology used.
That said, this map suggests that the area between Brevard and Volusia counties could see 10 feet of surge.
TIDES: Melbourne Beach will have a high tide at 12:23AM Thursday night; Jupiter gets it at 12:44AM... that's not great timing for there and all points between, but the next low tide is 5½ hours later, so that's good news for the area from Sebastian Inlet through Cape Canaveral.
Disclaimer: I lived in Melbourne for 11+ years... saw 1 minimal hurricane (Erin) and rode that out, 5 miles from the ocean. I would be leaving for this.
IIRC, Kennedy Space Center structures are built to withstand Cat. 3 storms.