Tropical Cyclones from The Art of Dredgeing - Some practical advice from an experienced master

Rules of Thumb The Art of Dredging -  Know the limits of the tools you are using.

Guidlines For Avoiding Hurricanes at sea -  My post. The basics of the 1-2-3 and 34 kt rules and links to more details

Ships general go to sea in advance of Hurricanes rather then stay in port. For vessels which must remain in port the Navy publishes the guides below:

Hurricane Haven Handbook for the North Atlantic Ocean - U.S. Navy Publication on-line

Typhoon Havens Handbook for Western Pacific and Indian Ocean - Same as above for the Pacific

 NWS National Hurricane Center


a forecast of 10-foot seas in open waters means a mariner should expect to encounter a wave spectrum with many waves between 6 and 10 feet along with a small percentage of waves up to 16 feet and possibly even as large as 20 feet!

from NWS Significant Wave Heights

From Significant Wave Height by Tom Ainsworth, NWS Juneau, Alaska

The diagram above shows the distribution of wave heights at sea. Confusingly it looks somewhat like a wave but each dot represents a single wave so the y axis (labeled N)  is the number of waves and the x axis  (labeled H) is the height. The point H(s) is the value used in forecasts.

I recommend you also read this article Expecting the Unexpected Wave: How the National Weather Service Marine Forecasts Compare to Observed Seas as well from Robin Storm, same info but together give a good picture of the wave spectrum

It is important to note that the same relationship between the significant wave height, average wave height and so on, including the highest wave expected to be encountered does not change with wave height. Consider what that means when the forecast is for 35 foot seas.

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