Those who navigate any kind of vessel through the waterways of Southeast Alaska should know a few things about wind and ocean currents in the region.
In southeast Alaska, wind speed varies with the seasons. The windier part of the year is from late September to mid-April with average hourly wind speed around 10 mph. The wind speed at any location will vary depending on local topography.
Throughout the year, winds come from the south about 40% of the time. North winds occur about 15% of the time year-round.
The likelihood of east winds and west winds depends on the season. From early April to early November, winds come from the west about 45% of the time. During the remaining period, early November to early April, winds come from the east about 45% of the time. Of course, there is a gradual transition between these periods. Like wind speed, wind direction at any particular location is influenced by topography. Nearby mountains may block, divert, or funnel winds on a regular basis.
Afternoon Winds in the Summer
During the summer, wind speed and direction vary during a typical day. Winds tend to be calm in the morning. As the day progresses, the sun warms the air over the land which causes the air to rise . Cooler air moves from the ocean to the shore to replace the rising air mass. The result is a west wind blowing onshore. Typically, the west winds die down in the evening.
At times, winds change quickly which can create difficult conditions for boating. At some locations, winds may increase to 30 or 40 miles per hour in the afternoon. If this wind is blowing against a strong tidal current, it may create standing waves. As mentioned, mountains and valleys may funnel and concentrate the winds. The combination of these factors can cause dangerous conditions for navigation, especially for smaller vessels.
Straits and channels connected to the ocean are subject to rising and ebbing tides, driven primarily by gravitational forces from the moon and sun. In general, most of the time, tidal flow at a particular location consists of reversing currents: flowing in one direction for half the tidal cycle and flowing in the opposite direction for the remainder of the cycle.
Apart from these reversing tidal currents, the inland waterways of Southeast Alaska also have a permanent non-tidal current flowing constantly in the same direction. The straits and passages of SE AK are arranged irregularly along a diagonal line from northwest to southeast. The non-tidal current is known to travel through these marine waters from southeast to northwest, albeit with plenty of islands deflecting the flow. The non-tidal current is small but persistent in comparison to tidal currents.
Tidal flows are driven primarily by the pull of gravity from the moon and sun, but topography and bathymetry also play a huge role. In certain narrow waterways, tidal currents may reach high velocity, while at the same time, in other nearby channels, equally narrow, flows may be moderate. Some of the straits and narrows that are important for transportation can be dangerous when tidal currents are maximum.
Main Travel Routes with Potentially Dangerous Currents
------- ------------ -----------------------------------
Wrangell Narrows — Ferry route to Petersburg
Peril Strait / Sergius Narrows — Ferry route to Sitka
Grenville Channel — South of Prince Rupert BC
Other Routes — Less Dangerous Currents or Less Traveled
--------------------------------------------------------- Lituya Bay
— Entrance at Harbor Point North and South Inian Pass
— West of Icy Strait Icy Strait
— North Passage and South Passage Sitakaday Narrows
— South end of Glacier Bay Stephens Passage
— Southeast of Juneau, between mainland and Grand Island Snow Passage
— SW edge of Zarembo Island, east of Prince of Wales Island Eastern Passage / Blake Passage
— From Wrangell southeast to Ernest Sound Angoon
— Entrance to Kootznahoo Inlet Chatham Strait
— Between Baranoff Island and Admiralty Island Keku Strait
— Between Kupreanof Island and Kuiu Island Stikine Strait
— Between Zarembo Island and Etolin Island El Capitan Passage
— Between Prince of Wales Island and north side of Kosciusko Island Tonowek Narrows
— Between west side of Prince of Wales Island and Heceta Island Tlevak Narrows
— Between Prince of Wales Island and northern tip of Dall Island
In extreme cases, the volume of tidal currents surging through a narrow passage resembles an awe-inspiring and surreal river, a turbulent saltwater river that reverses direction. These places are referred to as tidal rapids or a tide race. Currents may reach 12 to 16 knots, with erratic flows and dangerous eddies. When a vessel becomes caught in an eddy, it may be difficult or impossible to steer.
Experienced boaters and mariners who travel the Inside Passage are very aware of the location of tidal rapids. Several of these dangerous passages are located on busy travel routes northeast of Vancouver Island.
Tidal Rapids near Vancouver Island
--------------------------------------- Seymour Narrows — up to 16 knots
Surge Narrows / Okisolo Wave
Dent Rapids / Gillard Passage / Yuculta Rapids - 10 to 12 knots
Greene Point Rapids
The safest time to travel through tidal rapids is during slack tide or at least when flows are at lower velocity and in a favorable direction. Plan ahead and time your arrival for when currents are most favorable. For this, you definitely need to consult current-prediction tables.
It’s also wise to think of strategies to deal with conditions that are worse than expected. For example, ahead of time, find out if there is a safe place to get out of rough water. There might be a side channel or other protected area where winds and currents are less.
During the summer, remember that west winds may develop in the afternoon and change the situation. So pay attention to changes in the wind.
Special Places for Kayakers and Seals
Among kayakers, a well-known tide race is Skookumchuck Narrows, 78 km northwest of Vancouver BC. In this channel, the current may reach16 knots. The difference in height of the water surface on either side of the rapids can exceed 2 meters. It is arguably the best place in the world to ride a standing wave in a kayak.
In southeast Alaska, there are dozens of other tidal rapids in obscure places, frequented mainly by seals. These locations will probably remain secret and undiscovered for the foreseeable future due to their extreme remoteness.