You can make explicit why it was not easy to stay in the harbor. Alternate translation: "harbor did not sufficiently protect docked ships during winter storms" (See: [[rc://en/ta/man/translate/figs-activepassive]])
This speaks about the season of winter as if it were a commodity that someone can spend. Alternate translation: "to stay there for the cold season" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "faces northwest and southwest" means the opening of the harbor was toward those directions. Alternate translation: "it opened to the northwest and southwest"
These directions are based on what one sees as one faces the setting sun. Northwest is a little to the right of the setting sun, and southwest is a little to the left of the setting sun.