For an introduction to the concepts underlying weather forecasting, see Predicting The Weather.
TV weather forecasters tend to talk about sun, rain and temperature. Sea kayakers are more interested in wind speed and direction and are better off getting their forecasts elsewhere.
Weather forecasts on the Web are very good and you don't need any meteorological knowledge to understand them.
The NOAA's weather site at http://weather.gov has a section of marine forecasts for the Pacific, Atlantic and Gulf coasts, Hawaii and the Great Lakes, including Small Craft Advisories and current sea temperatures. For more detailed information and a better idea what to expect in the next few days, there is the NOAA Ocean Prediction Center.
If you prefer something halfway between the two, try the Marine Forecast pages on The Weather Channel which has all you really need - wind speed, direction, sea state, surf height, air and sea temperatures, visibility, pressure, high and low tide, tidal range and a ten-day outlook.
For Canada, the Weather Office at www.weatheroffice.gc.ca has its Marine Weather For Canada page. If you check the forecast and the reports from weather stations and buoys you come up with wind speed, direction, sea state, air and sea temperatures, visibility, pressure and a 24-hour outlook
There is also the Marine Forecast page of The Weather Network with quick access to wind speed, direction, sea state, air temperature, visibility, pressure, high and low tide, tidal range and a 24-hour outlook.
NOAA Weather Radio transmits constantly throughout the USA, with information about the weather and other hazards such as red tides. North of the border the equivalent is Environment Canada's Weatheradio Canada service.
The broadcasts can be picked up using a VHF radio, an AM/FM radio, CB radio, some handheld GPS units, or a small portable weather radio intended to receive only weather broadcasts. Some weather radios turn on or sound an alarm automatically when a severe weather warning is broadcast. .
Some marine VHF radios have special weather radio features so the user can choose which weather and emergency alerts are received and to select broadcasts for particular regions of the USA and/or Canada.
In the USA, many National Weather Service forecast offices offer recorded marine and local forecasts as found on NOAA weather radio. The number to dial can usually be found in the telephone directory white/blue pages under "United States Government","Commerce Department", or "National Weather Service". Click here for more information.
There is also the Dial-A-Buoy service which lets you hear the latest coastal and offshore weather observations and the latest National Weather Service marine forecast. In the USA, dial 888-701-8992 and enter the five-digit code for the weather station you want.