Is the Marine Weather in Alaska really Unpredictable?

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?

This Afternoon
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.
Tuesday Night
Variable winds 5 kt or less. Partly cloudy. Seas around 2 ft.
Variable winds 5 kt or less. Partly sunny. Seas around 2 ft.
Wednesday Night
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.
Thursday Night
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.

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Yes, but it depends on the weather pattern as to how much. After awhile you get a feel for which forecasts can be trusted and which forecasts can have waves 10-12 foot higher than forecasted.

This also depends on the area. Off Hinchinbrook as discussed in the other thread there are often sudden larger than expected swells/steep waves from unusual directions. I’ve heard various reasons for this, like the bottom uplifting from the 1964 earthquake and the ground swell bouncing off Kayak Island. I don’t know which one is actually true, but it’s an area of concern.

Likewise lows spinning along the Aleutian Chain are fairly unpredictable. A little bit farther north and you can have winds building huge seas along the entire length so you have 50 footers in front of Dutch, and a little bit farther south and you don’t get much. is generally more accurate than the NOAA forecast, but the NOAA forecast is an important tool for wave height. Farther north into the Bering above St. Matthew, PredictWind seems to be more accurate.

Could you anchor offshore of Hinchinbrook with the provided forecast on say Tuesday? Sure. I’ve crossed the Columbia river bar multiple times when you could anchor on it. I wouldn’t though, and I don’t think it could be called hyperbole to say it would be imprudent.


I agree that there are situations and areas where the forecasts have higher levels of uncertainty. Being able to determine this on a case by case basis is a core skill required for good seamanship.


It could be that the typical foreign tanker captain simply thinks: “I anchor off Fujairah all the time, so I can anchor off here too.”

Basically; betting on the weather is analogous to making formal bets. What are the estimated odds, what do I have to gain if I win and what’s at risk if I lose?

The weather in the GOA is predictable in the sense that is always unpredictable. But the unpredictability is often a result of a skipper’s mind frame and tide.

Weather systems are far more frequent in the region, and the calms between more transitory, relative to temperate latitudes and the tropics. The skipper used to trade winds will be gulled by a lifetime of experience into a mind frame that the weather can’t possibly change so quick in the brief period of time he envisions anchoring in. But in Alaska they can. The skipper’s experience works against him.

When I was a kid I was fascinated by Bermuda Triangle legends. Once I had experience in the GOA and Bering Sea I understood perfectly what happened to those ships. In the GOA/BS things always go to shit in a hurry. Therefore, skippers reflexively bolt and batten down everything, often even on the hour-run from Dutch Harbor to Captains Bay, even though they are two bays on the same island. Skippers expect bad weather at any instant, and prepare accordingly.

But a captain used to trade winds and Caribbean skies is not so paranoid. I forget which ship was last seen with her cargo hatches open before she went down in the Bermuda Triangle. No mystery there. Bad weather came up from nowhere, and she essentially pulled an El Faro. Any cargo vessel running around the the GOA/BS with her cargo hatches open, even on a short run, is a chicken begging to be plucked.

Another aspect of “unpredictable weather” are tides. The speed of the wind matters less than the size of the waves, and waves can be altered by tide.

Cape Hinchenbrook is at the mouth of one of the entrances to Prince William Sound. Think of PWS as God’s own bathtub. Fill it up, then dump it over the floor. All that water pouring out is kinetic energy. When it collides with more kinetic energy (wind) you’re going to get turbulence (waves).

The phenomenon is more pronounced in Shelikof Strait and Unimak Pass. Go through Unalga Pass in the Aleutian Islands in flat calm weather and you can run into a five foot tall standing wave at certain states of the tide, as water rushes between the GOA and BS, no different than a river bar, though it is a big, ocean pass. Some mariners think the effects of tides on open water is to only be found at river bars etc. but the principle applies anywhere vast amounts of potential energy stored as high tides are unleashed, and it affects waves.

The effects are complex in a tidal basin of many thousands of square miles, but the observation, “Then suddenly the waves came out of nowhere!” can often be attributed to the fact that tidal energy clashed with a stiff wind, even though the vessel is miles offshore.

I am uncertain as to whether NOAA takes into account the state of the tide when predicting wave heights, or if they use just wind as a predictor.


Not all foreign (I.e. non-American) Masters think alike.

PS> Fujairah Anchorage is known to experience heavy squalls with little warning.

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I’m not familiar with that area.

But the pilot was not talking about just that area. He says there is no place anywhere in the Gulf of Alaska where a ship can anchor in open waters because of the unpredictable environmental conditions.

I didn’t really make it clear but the point I was trying to make is this particular forecast is about as good as it gets.

Talking about the forecast, not the place.

In North America weather generally moves west to east. I always thought West Coast weather more unpredictable than East Coast weather for this reason, on this side of the country the weather crosses vastly more reporting points than it does over on the other side.
When I taught my flight students weather, one exercise was guessing the weather three days out. What you learn is the SPEED may change, so keeping an eye on all the stations off to the west will let you know if the front is coming across ahead of schedule or behind. Off the Oregon coast or Alaska - probably not so much.

The NTSB investigating the Seacor lift boat said it capsized due to a squall that overtook it.

The duck boat sinking was due to a squall.

If it happens in “sheltered” places like these, why not in the ocean?
I’ve been in sudden squalls in the GOA, this year even.

That chance in the GOA is a VERY good reason not to anchor in the open ocean. It happens, it happens fast, and can/is be fatal

Squalls happen all over the world, in open waters, at sheltered anchorages and over land.

To be hit by a squall while sailing in open waters can be dangerous, especially for small ships/boats, ships in bad condition, or not being made properly seaworthy.

In Singapore we have a phenomena known as “Sumatras”:
They can pack wind of hurricane force (>64 kts.) and come suddenly on those without local knowledge. They are forecasted on public sources as: “possibility of squalls and thunder storms”, which is generally the case every day in Singapore.

Hundreds of ships are at anchor in Singapore waters on regulated anchorages at all times.

On unregulated anchorages in Malaysian and Indonesian waters around Singapore (known as OPL East and West) there are more ships at anchor, some with skeleton crew only. When a Sumatra hits it is good business for Damage Surveyors, since ships there frequently drag anchor and bang into each other.

The moral of the story; It may be less dangerous to anchor in open waters far from shore in GoA than in usually benign areas close to shore and with a lots of other ships at anchor in a confined space.

PS> Good forecasting and Searoom to drift in is more important for safe anchoring than the nationality of the ship, Master and crew.

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I agree, the words predictable / unpredictable are somewhat vague. More precise to say that a ship anchored in an exposed location is at risk of encountering unexpected weather.

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Here’s some guidance from the Coast Pilot wrt to some wind speeds that are considered a risk.


They’ve picked a gale and a storm as critical wind speeds.

These numbers are too high for a PCTC/PCC. According to the internet a 200 meter car ship has twice the windage (sail area) as a VLCC in ballast. But 35 and 50 kts might work for a rule of thumb for other types of ships.

When anchoring of course it’s not just the wind. The total loads have to be considered. For current I use 1 kt current is equivalent to 10 kts of wind speed. For tankers I’ve seen 1 kt current about equivalent to 20 kts wind speed.

They take into account tide factors on the pinpoint forecast with the MapClick feature but not for the general area forecast.

One thing NOAA tries to do and isn’t that good at is take into account the effect of the ice pack on wave height. Channels open up in the ice sheet and the waves can be 10-15 feet above the forecasted wave height for the area.

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Back when WBH29 ( Peggy Dyson) in Kodiak gave the high seas forecast daily on 4125 Khz it of coarse was from the National Marine Wx Service predictions. Listening to the Vessels checking in with WX observations I was often amazed at how different actual conditions were from predicted.
I suppose that one must remember that a prediction is just that, an educated guess.

IIRC my previous employer hired a well known firm to model the impact of wave patterns in the Gulf of Alaska on the structural integrity of our charted high tensile strength steel tankers (which kept cracking). They had to put in the program patterns that existed no where else in the world.

Amount and position of High Tensile steel is one of the first thing to check when inspecting a tanker for possible reuse as FSO/FPSO.
When intended for 20 years on location without docking it is important to avoid too much HT steel in the hull structure due to susceptibility to crack.

Yeah, that was a while ago, there have been big improvements in forecasting since then.

I recall there was another guy that worked for the NWS in, IIRC, Cold Bay that also used to read the forecast on 4125 kHz. He was evidently a meteorologist because the fisherman used to ask questions about the forecast rather than just ask for repeats that Peggy would do.

The reliably of the forecast is going to be very dependent on the initial conditions. If there are half dozen storms and fronts bouncing around in the Gulf than a 100 mile error in the forecast position is going to mean dramatic changes in the actual weather encountered at one particular position.

On the other hand if the vessel is in the middle of a high pressure system 1000 miles across the same 100 mile forecast error will have far less impact on the weather, especially just 24 hours out.

How the weather affects a particular area just a forecast is sometimes not sufficient as you say. Local knowledge and/or using the Coast PIlots would be more prudent .

For example Shelikof Strait:.

3 posts were split to a new topic: Not weather