|Frequently Asked Questions
related to Marine Weather & Observations
A Small Craft Advisory is issued to alert operators of small craft whenever sustained winds of 20 to 33 knots inclusive, and/or seas of 7 feet or greater, are either ongoing or forecasted to develop within the next 12 hours. This criteria is uniform for all U.S. Gulf of Mexico coastal waters, but may differ along the FFCantic or Pacific coasts. There is no official definition for the term "small craft" in the National Weather Service. However, the U.S. Coast Guard considers any vessel less than or equal to 33 feet to be a small craft. The smallest, most weather-sensitive boats can experience problems in lower winds and seas. For this reason, the headline, "Small Craft Exercise Caution," is placed in the forecast for current or predicted winds of 15 to 20 knots and seas of 4 to 6 feet.
A Gale Warning is issued to alert all mariners whenever sustained winds of 34 to 47 knots, associated with a non-tropical system, are either ongoing or forecasted to develop within the next 12 hours. Winds in this range associated with a tropical system would be covered under a Tropical Storm Warning (34 to 63 knots). Sustained winds above 47 knots outside of tropical systems are very rare in the Gulf of Mexico. However, if these conditions are observed or predicted, a Storm Warning will be issued. Beginning in 2008, NWS began issuing Gale Watches. These give an extra heads up that gale conditions are possible and are issued 24-48 hours ahead of an anticiapted event.
Visit the National Data Buoy Center web pages for this data. Their main page is found at at http://www.ndbc.noaa.gov/rmd.shtml. NDBC is the organization that maintains the nation's buoy network. To learn more about the NDBC, take their online Virtual Tour. Also be sure to check out their FAQ page.
Occasionally, a sensor on one of the buoys or platforms malfunctions. This can occur for a number of reasons including exposure to the elements, collision with watercraft, or simply old age. Data outages are intended to be temporary. To determine if a particular sensor has failed, refer to the latest weekly status report from NDBC, particularly the Remarks sections. If your sensor of interest has failed, check to determine if and when station maintenance has been scheduled.
The buoys in all five Great Lakes are retrieved seasonally to prevent them from being damaged by lake ice. Typically, the buoys are removed in November or December and returned to service in April.
Significant wave height is the mean (or average) of the highest 1/3 of the waves observed by the buoy during the wave sensing period. The buoys measure the wave heights using an accelerometer which measures the vertical acceleration of the buoy every 2/3 of a second over a 20 minute sampling period. Significant wave height is what we try to forecast in the National Weather Service.
The wind wave height is that portion of the significant wave height that was caused by the local wind. The remaining portion is listed as swell height. Swells are older waves that migrated into the local area but were generated by the wind at some distant location at some time in the past.
The type of mooring used depends on the hull type of the buoy, the location of the buoy, and the water depth. For example, a smaller buoy in shallow coastal waters is moored using an all-chain mooring. On the other hand, a large discus buoy deployed in deep ocean requires a combination of chain, synthetic nylon, and polypropylene. Moorings are designed for a 6-year life, but often last 10 years. The moorings occasionally break allowing the buoy to go adrift. If possible, the buoys are retrieved and redeployed. Click here to see a graphic of the various buoy moorings.
1kt = 1.15mph. In other words, take the winds speed in knots and multiply by 1.15 to get mph. By the way, a knot is a nautical mile per hour. To convert other meteorological parameters, refer to this on-line weather calculator.
Please refer to this Marine FAQ page maintained by our national headquarters. Hopefully you'll find your answers there. If not, give us a call during normal business hours at (850) 942-8833, ext. 1.