Thirty-three Years of Annual Atlantic Hurricane Season Outlooks
Comparison of Weather Research Center Cyclone Strike Index with Colorado
State University’s Hurricane Outlook
By: Jill F. Hasling, Certified Consulting Meteorologist
Houston, Texas
www.wxresearch.com/outlook
April 2017
When the Weather Research Center’s Hasling - Freeman Cyclone Strike Index [WRC] Annual Atlantic
Hurricane Outlook is compared to Colorado State University’s Dr. Bill Gray’s seasonal hurricane outlook
[GRAY], and Climatology, WRC’s outlook edges out both. In 1985, Jill F. Hasling and Dr. John C. Freeman
developed a seasonal hurricane outlook model to forecast which section of the United States coast had
the highest risk of experiencing the landfall of a tropical storm or hurricane. Thirty-three years of
outlooks have been made from 1984 to 2016 and only four years 1984, 2006, 2010 and 2014 failed to
have a landfall for the part of the coast with the highest risk of landfall in that season. So 29 out 33 years
gives WRC outlook a 88% accuracy rate.
Around the same time, Professor Bill Gray at Colorado State University started making an Atlantic
Hurricane Season Outlook which gave the total number of named storms, the number of hurricanes, the
number of hurricane days and the number of tropical storm days. WRC’s model was used to give
secondary predictions of these parameters, so the author did a comparison between the two outlooks
since 1984. Figure 1 shows the difference between the number of observed named storms in the Atlantic
and the WRC Outlook and GRAY’s Outlook. The red line in Figure 1 indicates the error which is the
difference between the number of storms forecasted by the WRC’s outlook and the actual number of
Atlantic tropical cyclones [named storms] each year. The blue line is the GRAY outlook error. For example
in Figure 1 for the year 1988, the WRC Outlook predicted 5 tropical cyclones and GRAY’s April seasonal
outlook predicted 7 named storms. WRC predicted had an error of 0 and GRAY had an error of +2. Out
of the thirty-three years [1984 to 2016], WRC’s Outlook for the total number of tropical cyclones was
within one cyclone nine of the years. GRAY’s outlook was within one cyclone eight of the years.
The same procedure was applied to the prediction of the number of hurricanes each year. The forecast
error is plotted in Figure 2. This shows the difference between the number of observed hurricanes in the
Atlantic and WRC Outlook and GRAY outlook. Out of the thirty-three years, the WRC outlook predicted
the number of hurricanes within one hurricane for fourteen of the thirty three years. GRAY’s outlook was
within one hurricane twelve of the thirty-three years .
The number of hurricane days expected each year was also predicted. Figure 3 shows the difference
between the actual number of hurricane days in the Atlantic and WRC Outlook and GRAY’s Outlook. Out
of the thirty-three years, the number of hurricane days predicted by the WRC was within five days twelve
of the thirty-three years. For the GRAY outlook, nine of the thirty three years were within five days.
The same procedure to determine the error in the predicted of the number of tropical storm days was
performed. Figure 4 shows the difference between the actual number of tropical storm days in the
Atlantic and the WRC Outlook and GRAY Outlook. The actual number of tropical storm days within ten
days was predicted by the WRC outlook fifteen the years. For the GRAY outlook, eleven of the years were
within ten days. Table 1 gives a summary of these outlooks.
+-Number of Tropical Cyclones Actual from Outlookst
WRC Error
GRAY APR Error
+-1
+-1
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
-12
-13
-14
-15
-16
-17
-18
Figure 1: Difference plus or minus one between the number of actual tropical cyclones [named storms
and hurricanes] for WRC’s and GRAY’s Outlook.
+-Number of Hurricanes Observed versus WRC's and GRAY's Outlooks
WRC Error
GRAY Error
Figure 2: : Difference plus or minus one between the number of actual hurricanes for WRC’s and GRAY’s
Outlook.
2016
2015
2014
2013
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
+-Number of Hurricane Days Actual versus Outlooks
WRC Error
GRAY Error
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
45
40
35
30
25
20
15
10
5
0
-5
-10
-15
-20
-25
-30
-35
-40
-45
Figure 3: Difference plus or minus between the number of observed hurricane days, selected outlook
70
+-Number of Storm Days Actual versus WRC's and GRAY's
WRC Error
GRAY ErrorOutlook
60
50
40
30
20
10
0
-10
-20
-30
-40
-50
-60
-70
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
-80
Figure 4: Difference plus or minus ten days between the number of actual tropical storm days and
WRC’s and GRAY’s outlook
Table 1: Summary of Outlook Comparisons 1984 to 2016 [33 Years]
WRC OUTLOOK
GRAY
OUTLOOK
CLIMATOLOGY
Number of Named
Storms in Atlantic
within 1 storm
10 Years
9 Years
4 Years
Number of
Hurricanes in
Atlantic within 1
storm
14 Years
12 Years
9 Years
Number of Named
Hurricane Days in
Atlantic within 5
days
12 Years
11 Years
7 Years
Number of
Tropical Storm
Days in Atlantic
within 10 Days
14 Years
12 Years
7 Years
In 2000, NOAA started making Annual Atlantic Hurricane Outlooks. Also at that time with better observing
techniques, it seems that the number of observed storms increased. So the decision was made to increase
the total number of named tropical storms by 3 storms each year and the number of hurricanes by one
after 2000. This would change the numbers for the WRC’s CSI outlook by the following, see Table 2.
Table 2: Corrected WRC Outlook to Increase Named Storms and Hurricanes after 1999
Number of Named
Storms in Atlantic
within 1 storm
Number
of
Hurricanes
in
Atlantic within 1
storm
WRC OUTLOOK
GRAY
OUTLOOK
13 Years
9 Years
15 Years
12 Years
WRC’s Outlook was developed to predict which section of the United States coast line had the highest risk
of experiencing a landfall of a tropical storm or hurricane each year. Below is the outlook from 2017 to
2039. When using this outlook, remember that it states which section of the coast has the highest risk,
each year each section of the coast has a risk of experiencing landfall of a tropical cyclone.
No. of
No,
Hurricane
Cyclones Hurricanes
Days
Tropical
Storm
Days
Year
Coast
2017
Texas 70% W. Florida 70%
13
6
25
73
2018
Louisiana to Alabama 75%
13
5
14
30
2019
Louisiana to Alabama 75%
13
5
14
30
2020
Georgia to N. Carolina 90%
14
6
28
88
2021
Louisiana to Alabama 70%
10
5
11
52
2022
11
6
29
62
2023
W. Florida 90%
Louisiana to Alabama 90% W.
Florida 90%
13
7
34
74
2024
Georgia to N. Carolina 60%
Louisiana to Alabama 60% W.
Florida 60%
11
6
24
63
2025
Louisiana to Alabama 70% W.
Florida 70%
12
7
24
69
2026
9
4
19
46
2027
W. Florida 80%
NE Coast 70% Georgia to N.
Carolina 70%
10
6
25
55
2028
W. Florida 70%
10
5
20
60
2029
Texas 70% W. Florida 70%
13
6
25
73
2030
Georgia to N. Carolina 90%
14
6
28
88
2031
Louisiana to Alabama 70%
10
5
11
52
W. Florida 90%
11
6
29
62
13
7
34
74
11
6
24
63
12
7
24
69
2032
2033
2034
2035
2036
Louisiana to Alabama 90% W.
Florida 90%
Georgia to N. Carolina 60%
Louisiana to Alabama 60% W.
Florida 60%
Louisiana to Alabama 70% W.
Florida 70%
9
4
19
46
2037
W. Florida 80%
NE Coast 70% Georgia to N.
Carolina 70%
10
6
25
55
2038
W. Florida 70%
10
5
20
60
2039
Texas 70% W. Florida 70%
13
6
25
73