At 0600 this morning, the NOAA weather buoy at Smith Island which is the nearest one to us was reporting sustained winds of 44 knots with gusts to 50 knots (almost enough to make you want to put a reef in the main!). This is the result of a 953 millibar low out in the Pacific just west of Vancouver Island. I was just reading a chapter on meteorology in Peter Bruce's updated version of Adlard Coles Heavy Weather Sailing. Richard Ebling the British meteorologist who wrote the chapter says that surface winds on the water are 20% below the wind speed above a "friction layer" and that wind speeds at the surface on land are 40% below the wind speeds above the friction layer. He suggests that forecasted wind speeds are already adjusted to a level about 100 feet off the water (maybe this is only a UK thing?. So my question is this: When we read about reported 50 knot winds, is that at the surface, at the top of the mast, or projected to some theoretical level 100 feet up? Any techies out there that can shed any light on this? Thanks. Gary Wyngarden S/V Shibumi H335
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Lopez Wind 45 MPH
I don't have an answer to your question, but on Lopez at 9am we had a gust at 45 mph. The Smith Isl. station is not high off the water so the wind speed I expect would be established at the height of the instrument location. It is true that the land friction reduces wind speed. The same holds true of a river where the center flows faster then the edges. Enjoy spring. Herb Drifter/26 O'Day, Lopez Island, Washington
I don't have an answer to your question, but on Lopez at 9am we had a gust at 45 mph. The Smith Isl. station is not high off the water so the wind speed I expect would be established at the height of the instrument location. It is true that the land friction reduces wind speed. The same holds true of a river where the center flows faster then the edges. Enjoy spring. Herb Drifter/26 O'Day, Lopez Island, Washington
Surface wind
Have done a bit of wx forecasting and analysis in my time, and I believe the winds reported are actually the winds observed by the sensor. In other words, wind observations are typically not adjusted for height; they are the winds the anemometer "sees/senses" at its height above the surface, be it located on a building, a tower, or aboard ship. That being said, reported winds are usually averaged over time (2 minutes in the U.S., according to U.S. National Weather Service Standards). As sailors know, there can be tremendous variations in surface winds over relatively short horizontal distances (America's Cup boats send someone aloft to look for wind lines.) There can be substantial variations in wind over larger horizontal distances, as folks who've observed winds generated by topographic funneling upwind of the Gulf of Tehuantepec, on the Pacific side of Central America. (See related link) -Rich
Have done a bit of wx forecasting and analysis in my time, and I believe the winds reported are actually the winds observed by the sensor. In other words, wind observations are typically not adjusted for height; they are the winds the anemometer "sees/senses" at its height above the surface, be it located on a building, a tower, or aboard ship. That being said, reported winds are usually averaged over time (2 minutes in the U.S., according to U.S. National Weather Service Standards). As sailors know, there can be tremendous variations in surface winds over relatively short horizontal distances (America's Cup boats send someone aloft to look for wind lines.) There can be substantial variations in wind over larger horizontal distances, as folks who've observed winds generated by topographic funneling upwind of the Gulf of Tehuantepec, on the Pacific side of Central America. (See related link) -Rich
We had a gust of 76 but I don't know if it was
miles be hour or knots. That was in Bellingham Bay in the early morn. So far all the lines are holding but the boat is really healing over at times tied to the dock. Apprently we have several more days of high winds....
miles be hour or knots. That was in Bellingham Bay in the early morn. So far all the lines are holding but the boat is really healing over at times tied to the dock. Apprently we have several more days of high winds....
Actual Met Bureau definitions - Australian
- The following are extracts from the weather bureaus site - the warning about gusts being 40% higher was introduced as a direct result of the lack of what weather reports actually meant during the tragedy of the 1998 Sydnet Hobart race where 6 sailors perished in winds up to 80 plus knots and huge seas caused by wind over current. *********** ----------- PLEASE BE AWARE, wind gusts can be a further 40 percent stronger than the averages given here, and maximum waves may be up to twice the height. Additional notes: The wind is a continuous succession of gusts and lulls (quiet intervals) associated with equally rapid changes of direction over a range which may exceed 30°. The mean wind speed over a period of time is therefore the mean of many gusts and lulls. Usually only the mean wind is forecast, unless the gusts are expected to be a significant feature. For instance, Fresh, gusty southwest winds indicates that the mean wind speed will be between 17 and 21 knots and the mean wind direction will be from the southwest, but that there will also be gusts to speeds significantly higher than the mean. Gust: a gust is any sudden increase of wind of short duration, usually a few seconds. Squall: a squall comprises a rather sudden increase of the mean wind speed which lasts for several minutes at least before the mean wind returns to near its previous value. A squall may include many gusts. Wind descriptions (derived from the Beaufort Wind Scale): wind speeds are given as the equivalent speed at a standard height of 10 metres above open flat ground
- The following are extracts from the weather bureaus site - the warning about gusts being 40% higher was introduced as a direct result of the lack of what weather reports actually meant during the tragedy of the 1998 Sydnet Hobart race where 6 sailors perished in winds up to 80 plus knots and huge seas caused by wind over current. *********** ----------- PLEASE BE AWARE, wind gusts can be a further 40 percent stronger than the averages given here, and maximum waves may be up to twice the height. Additional notes: The wind is a continuous succession of gusts and lulls (quiet intervals) associated with equally rapid changes of direction over a range which may exceed 30°. The mean wind speed over a period of time is therefore the mean of many gusts and lulls. Usually only the mean wind is forecast, unless the gusts are expected to be a significant feature. For instance, Fresh, gusty southwest winds indicates that the mean wind speed will be between 17 and 21 knots and the mean wind direction will be from the southwest, but that there will also be gusts to speeds significantly higher than the mean. Gust: a gust is any sudden increase of wind of short duration, usually a few seconds. Squall: a squall comprises a rather sudden increase of the mean wind speed which lasts for several minutes at least before the mean wind returns to near its previous value. A squall may include many gusts. Wind descriptions (derived from the Beaufort Wind Scale): wind speeds are given as the equivalent speed at a standard height of 10 metres above open flat ground
All I know is...
...glad I wasn't cruising by Smith Island this morning. It's sloppy enough in good weather!
...glad I wasn't cruising by Smith Island this morning. It's sloppy enough in good weather!
weather bouy
Last time I saw a weather bouy, it was sitting pretty close to sea level. I think the readings you get from it would be accurate for sailing. Of course, if you went on to the NOAA website to get the information, I am sure they have an email address to get the official answer from.
Last time I saw a weather bouy, it was sitting pretty close to sea level. I think the readings you get from it would be accurate for sailing. Of course, if you went on to the NOAA website to get the information, I am sure they have an email address to get the official answer from.
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