28 FEBRUARY 2003
DATA SET PAGES 17 AND 18: WIND SUMMARY. Figures 2-17 and
2-18 are samples of Data Set Page 17 and Data Set Page 18, respectively.
Explanation of Charts
These charts depict the frequency of different wind direction and wind
speed combinations. The observations are binned into the 16 cardinal compass
directions and 5 speed categories (1 to 5 knots, 6 to 14 knots, 15 to 24 knots, 25 to 34
knots, and greater than 34 knots). The frequency of direction and the tick marks
indicate that values lie along each "spoke" of the wind chart. The wind speed bins for
each direction are color coded by the legend at the bottom of the chart.
To determine the percent frequency of a particular wind direction, look for
the tick mark bounding the outer edge of a colored (wind speed) area. In the case of
the first wind speed bin (1 to 5 knots), the percent frequency is simply the value of the
tick mark on the outer edge of the 1 to 5 knot region. For the higher speed bins (6 to 14
knots or greater), subtract the earlier spoke values from the value shown to get the
frequency for the speed bin in question.
The values for percent frequency have been summed by direction, so to
determine the total percent frequency for all speeds from a particular direction, look up
the tick mark (or interpolated value) bounding the outermost colored area along that
spoke. That tick mark represents the total percent frequency of wind from that direction.
Since the calm condition has no direction, the percent occurrence of calm
conditions is displayed immediately below the chart.
Wind Summary Chart Example. The wind summary charts are prepared
by 3-month seasons, over all hours (e.g., December, January, February for northern
hemisphere winter or southern hemisphere summer; March, April, May for northern
hemisphere spring or southern hemisphere fall). See the December through February
sample wind summary chart in Figure 2-17 for an example of determining percent
From the December through February sample wind summary chart, the
percent frequency of wind between 1 to 5 knots and from the north (N) is about 3%.
The percent frequency of wind between 6 to 14 knots and from the northwest (NW ) is
about 5% (7% minus 2%). The percent frequency of all wind speeds from the south (S)
is about 12%. The percent frequency of all wind directions from the west through north
(W , W NW , NW , NNW , and N) is about 38% (5% + 7% + 8% + 8% + 10%,
respectively). It is easy to determine that wind speeds greater than 34 knots almost
never occur (or are such a small frequency from any direction) because the colored
area (yellow) is not shown or is indistinguishable because it is extremely small.
The percent of time the wind is calm is indicated in the lower left corner of
the chart--in this case, 12.82%. W hen the outermost value from each of the 16
directions are summed and added to the percent calm, the result is 100% (allowing for