This is the statement from the SW Alaska Pilot from another thread.
Anchoring in open waters in the Gulf of Alaska is at best imprudent, and at worst negligent, given the unpredictable environmental conditions which may be encountered at any time of the year.”
In a sense it is literally true the weather cannot be predicted in general but mariners don’t think of the problem that way. The question is what are the probabilities of error, the possible amount of error and the consequences for the ship in the case the forecast (as opposed to a prediction) is in error.
The simplest way to make a forecast is to look at current and past trends and assume that those trends will continue. If the ship can be gotten ready in a couple hours only need to look ahead a few hours. Worse case scenario if the captain is a heavy sleeper a good 12 hour forecast is needed.
With this forecast what are the chances that an off-shore anchorage will be untenable in the next 12 to 24 hours?
W wind around 10 kt. Sunny. Seas around 2 ft.
SW wind 5 to 10 kt. Mostly clear. Seas around 2 ft.
Variable winds 5 kt or less. Mostly sunny. Seas around 2 ft.
Variable winds 5 kt or less. Partly cloudy. Seas around 2 ft.
Variable winds 5 kt or less. Partly sunny. Seas around 2 ft.
Variable winds 5 kt or less. Showers likely, mainly after 4am. Seas around 2 ft.
E wind 5 to 10 kt. Rain likely, mainly before 10am. Seas around 2 ft.
ESE wind 15 to 20 kt. Rain likely. Seas 4 ft building to 7 ft.
E wind around 20 kt. Rain likely. Seas around 7 ft.
There are also a couple checks to this method, typically night orders include boilerplate lines requiring a call changes in the weather (rapid falling barometer, increase in winds etc).
This method of assuming weather patterns are going to continue can also be checked against the weather services forecasts, 24 hr, 48 hr etc.