National Hurricane Center Forecast Verification
Updated 3 April 2013
Contents
- Introduction
- Forecast verification
procedures
- Annual NHC verification
reports
- Official five-year mean errors and distributions
- Official error trends
- Model error trends
- NHC official forecast
error database
- Performance measures and
goals
- References
4. Official five-year mean errors and distributions
Due to the natural
volatility in tropical cyclone track characteristics, annual
errors can vary significantly from year to year. For example,
years dominated by tracks through the low latitude easterly trade
winds typically have relatively small annual errors. Conversely, a
relatively large number of forecasts in the mid-latitude
westerlies (as can occur during El Niņo years) can lead to larger
errors. Consequently, representative or stable error
characteristics must be obtained using a longer period of record.
NHC uses a 5-year sample
to define its current forecast error characteristics.
Average errors for the last 5 period are given below.
These verifications follow the procedures given above in Section 2 (i.e., they include the
subtropical and depression stages) and the sample is homogeneous
with the operational CLIPER5 and Decay-SHIFOR5 models.
Mean official track and
intensity forecast errors for the 5-year period 2008-2012 (.pdf)
The distributions of
5-year track and intensity errors are given graphically in the
figures below.
Cumulative
distribution of five-year official Atlantic basin tropical
cyclone track forecast errors.
Diagram shows the
percentage of official forecasts having an error less than the
value along the y-axis. For example, to determine the fraction of
24 h forecasts having an error smaller than 100 n mi, find 100 n
mi on the y-axis, and read across the diagram until this value
intersects the red (24 h forecast) line. Then read down to obtain
the percentage.
These track error
distributions are used to set the size of the "forecast error
cone" displayed on NHC track forecast web graphics. In these
graphics, the cone represents the probable track of the center of
a tropical cyclone, and is formed by enclosing the area swept out
by a set of circles along the forecast track (at 12, 24, 36 hours,
etc). The size of each circle is set so that two-thirds
(67%) of historical official forecast errors over a 5-year sample
fall within the circle. The circle radii defining the error cone
in 2011 for the Atlantic basin
are given in the figure above.
Cumulative
distribution of five-year official Atlantic basin tropical
cyclone intensity forecast errors.
Diagram shows the
percentage of official forecasts having an error magnitude less
than the value along the y-axis. For example, to determine the
fraction of 24 h forecasts having an error smaller than 20 kt,
find 20 kt on the y-axis, and read across the diagram until this
value intersects the red (24 h forecast) line. Then read down to
obtain the percentage.
Cumulative
distribution of five-year official eastern North Pacific basin
tropical cyclone track forecast errors.
Diagram shows the
percentage of official forecasts having an error less than the
value along the y-axis. For example, to determine the fraction of
24 h forecasts having an error smaller than 100 n mi, find 100 n
mi on the y-axis, and read across the diagram until this value
intersects the red (24 h forecast) line. Then read down to obtain
the percentage. The size of the cirlcles defining the
forecast error cone in 2011 for the eastern North Pacific basin
are given in the figure above.
Cumulative
distribution of five-year official eastern North Pacific basin
tropical cyclone intensity forecast errors.
Diagram shows the percentage of official forecasts having an error
magnitude less than the value along the y-axis. For example, to
determine the fraction of 24 h forecasts having an error smaller
than 20 kt, find 20 kt on the y-axis, and read across the diagram
until this value intersects the red (24 h forecast) line. Then
read down to obtain the percentage.
Next: Official error trends
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