If you're starting out brand new, or if you're setting out after having been in port for a while, probably just a random D10 for the starting weather value.
Good clarification to add; thanks for asking!
EDIT: Additional thoughts. Do any of these seem better choices?
The same rules would apply after the ship has been in port for more than a week (unless you want to keep tracking weather while in port). But the idea of landfall and port as something of a reset makes sense, and makes it a more significant event in that way. Also, the weather over land follows different rules from at sea, so it makes sense not to use the sailing Wind/Weather rules while in port, and have a reset once you're out on the open seas once more.
- You could treat it like after a Stormfront, (use wind 4, Weather 5) I'd be tempted to do that for any brand new start.
- You could generate new Wind and Weather numbers randomly. For each, roll 2d10 and average them (rounding up). Carryover modifiers (to next roll) would apply, but adjustments to the starting numbers would be waived, and Tide does not apply while in Port. So Wind results of 1, 2, 8-10 would have modifiers applied to the first new turn Weather. But Weather results like "2 Drizzle/fog/light rain; -2 Wind, -1 to next wind roll" would only use the -1 to next roll.