Charles Ellicott Commentary Acts 27:9

"And when much time was spent, and the voyage was now dangerous, because the Fast was now already gone by, Paul admonished them," — Acts 27:9 (ASV)

Because the fast was now already past.—The Fast was the Jewish Day of Atonement, which fell on the tenth of Tisri (in that year, September 24th), the seventh month of the Jewish ecclesiastical year. The sailing season with the Jews was reckoned from the Feast of Pentecost to that of Tabernacles, which fell five days after the Fast.

Roman reckoning gave a somewhat wider range, namely, from the sixth day of the Ides of March to the third of the Ides of November. The manner in which St. Luke names the Fast, and not the Feast of Tabernacles, makes it probable that the time to which we have now come was between September 24th and October 1st, when the Etesian winds, which are always of the nature of equinoctial gales, would naturally be most violent.

Probably, also, the date may have been fixed in St. Luke’s memory by St. Paul’s observance of the Fast. He was not likely to leave so memorable a day unobserved, however little he might care to impose its observance upon others. To keep the Feast of Tabernacles on board the ship was, of course, impossible.