Key Biscayne drivers are still paying $5.79 a gallon for regular gas, a price that hasn't budged in three weeks, even as the Miami metro average climbed back up to $3.93 during the first week of back-to-school traffic.

The $1.86-per-gallon premium over the metro average means a 15-gallon fill-up on the island costs nearly $28 more than at an average Miami station. With Miami-Dade public schools reopening Thursday, Aug. 13, the timing hits island families and commuters crossing the Rickenbacker Causeway just as daily driving picks up again.

Both Key Biscayne stations have charged $5.79 since July 27, according to weekly price data from the Islander News, which tracks GasBuddy's survey of 1,690 Miami-area stations. The island's price jumped 30 cents in a single week in late July, rising from $5.49 on July 20 to $5.79 on July 27, and has stayed flat since.

The price hasn't moved.

Meanwhile, the broader Miami market reversed a brief dip. The metro average rose 4.6 cents over the week ending Monday, Aug. 10, and now sits 4.2 cents higher than a month ago and 95 cents above where it was a year ago. The cheapest station in Miami was selling regular for $3.57 on Sunday, Aug. 9; the most expensive hit $5.99.

Nationally, prices moved the other way. The U.S. average fell 10.7 cents to $3.94 per gallon, with 47 states posting declines.

"For now, enjoy the dip, but keep a close eye on how the Strait situation develops in the days ahead," Patrick De Haan, head of petroleum analysis at GasBuddy, said in a weekly news release, referring to the ongoing closure of the Strait of Hormuz, a critical oil shipping lane. De Haan warned that if geopolitical tensions persist, the national average "could climb to its highest level ever recorded this late in the calendar year."

The island's premium has narrowed slightly from the prior week, when the metro average sat lower at $3.89, but only because Miami prices rose while Key Biscayne stayed put.

GasBuddy's next weekly update is expected Monday, Aug. 17.