NASA/TP—2010–216429

An Estimate of the North Atlantic Basin

Tropical Cyclone Activity for the 2010

Hurricane Season

Robert M. Wilson

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

May 2010
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NASA/TP—2010–216429

An Estimate of the North Atlantic Basin

Tropical Cyclone Activity for the 2010

Hurricane Season

Robert M. Wilson

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

National Aeronautics and

Space Administration

Marshall Space Flight Center • MSFC, Alabama 35812

May 2010
Available from:

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076 –1320

443 –757– 5802

This report is also available in electronic form at

<https://www2. sti.nasa.gov>
TABLE OF CONTENTS

1. INTRODUCTION ............................................................................................................... 1

2. RESULTS AND DISCUSSION ........................................................................................... 2

2.1 Statistical Aspects of the North Atlantic Basin Tropical Cyclones (1950–2009) ........... 2

2.2 First Differences of Parametric 10-yma Values ............................................................ 4

2.3 Armagh Observatory (Northern Ireland) Surface-Air Temperature

and Correlations Against It Based on 10-yma Values ................................................... 6

2.4 Comparison of Armagh Observatory (Northern Ireland) Surface-Air Temperatures

and Mauna Loa Carbon Dioxide Atmospheric Concentration Measurements

Basedon 10-yma Values ............................................................................................... 10

2.5 El Niño Southern Oscillation Cycle Effects .................................................................. 14

2.6 The Relationship Between the Annual Mean Oceanic Niño Index and the Annual

Mean Surface-Air Temperature at Armagh Observatory ............................................. 19

2.7 Predicting Yearly <ONI> From the January–May Average and Prediction

of Warmest and Coolest Monthly ONI Value .............................................................. 22

2.8 Predicting the 2005 10-yma Values for NTC, NH, NMH, and NUSLFH

From the Expected 10-yma Values of <AT> and <ONI> and the Yearly

Frequenciesfor 2010 .................................................................................................... 24

2.9 Comparison With Colorado State University and Tropical Storm Risk Estimates ....... 24

2.10 Predicting the Next El Niño Southern Oscillation Extreme Event Occurrence ............. 27

3. SUMMARY .......................................................................................................................... 29

REFERENCES......................................................................................................................... 33
LIST OF FIGURES

1. Yearly frequencies of (a) NTC, (b) NH, (c) NMH, and (d) NUSLFH

for the North Atlantic basin (1950–2009) ................................................................ 3

2. First differences of the 10-yma values of (a) NTC, (b) NH, (c) NMH,

and(d) NUSLFH .................................................................................................... 5

3. Armagh observations for the interval 1950–2009: (a) Yearly mean <AT>

and (b) first differences of the 10-yma values of <AT> ........................................... 7

4. Scatter plots of the 10-yma values of (a) NTC, (b) NH, (c) NMH,

and (d) NUSLFH against 10-yma values of <AT> ................................................. 9

5. 10-yma values of MLCO2 ........................................................................................ 11

6. Scatter plot of 10-yma values of <AT> against 10-yma values of MLCO 2 ............. 12

7. Observations of ONI: (a) Yearly mean <OCI> and (b) first differences

of the 10-yma values of <ONI> .............................................................................. 18

8. Scatter plot of 10-yma values of <ONI> against 10-yma values of <AT> .............. 22

9. Scatter plot of <ONI> against the January–May average value of ONI .................. 23

10. Scatter plot of (a) the warmest and (b) the coolest monthly ONI value against

theyearly mean <ONI> .......................................................................................... 25

11. Scatter plot of RP against duration for EN events ................................................... 27

12. Scatter plot of RP against duration for LN events ................................................... 28

iv
LIST OF TABLES

1. Correlations of NTC, NH, NMH, and NUSLFH versus <AT> using 10-yma

values for the intervals 1995–2004 and 1950–2004 ..................................................... 10

2. Listing of EN and LN events based on ONI (ERSST.v3b) ....................................... 15

3. Frequency distribution of onset, peak, and end dates for EN and LN events ............ 16

4. Comparison of <ONI> and NLNM, NNM, and NENM ........................................ 19

5. Distribution of (a) NLNM/yr, (b) NNM/yr, and (c) NENM/yr

versus <ONI> yearly value ....................................................................................... 20

6. Observed and predicted 10-yma parametric values for 1995–2004 ............................. 26

7. Predictions of 10-yma parametric values for 2005 based on the interval 1995–2004 .. 26

v
LIST OF ACRONYMS AND SYMBOLS

<<ONI>> Oceanic Niño Index event average

<AT> annual mean surface-air temperature at Armagh Observatory

<ONI> annual mean Oceanic Niño Index

10-yma 10-year moving average

2-mma 2-month moving average

CO2carbon dioxide

CSU Colorado State University

EN El Niño

ENSO El Niño Southern Oscillation

ERSST.v3b Extended Reconstruction of Sea Surface Temperature, version 3b

LN La Niña

M moderate

max ONI maximum Oceanic Niño Index value

MLCO2

Mauna Loa carbon dioxide atmospheric concentration

NENM number of El Niño months

NH number of hurricanes

NLNM number of La Niña months

NMH number of major hurricanes

NNM number of El Niño Southern Oscillation neutral months

NOAA National Oceanic and Atmospheric Administration

NTC number of tropical cyclones

NUSLFH number of United States land-falling hurricanes

ONI Oceanic Niño Index

PWS peak wind speed

RP recurrence period

S strong

SST sea surface temperature

TSR Tropical Storm Risk

U.S. United States

W weak

vi
NOMENCLATURE

cl confidence level

fd (x)10 first difference of parameter x using 10-yma values

P probability

r coefficient of correlation

r2 coefficient of determination

sd standard deviation

se standard error of estimate

x x parameter

x x regression

y y regression

y 1 y regression based on current activity level (since 1995)

y2 y regression based on overall interval (since 1950)

y3 y regression based on first more active interval (1950–1965)

vii

TECHNICAL PUBLICATION

AN ESTIMATE OF THE NORTH ATLANTIC BASIN TROpICAL CYCLONE

ACTIvITY FOR THE 2010 HURRICANE SEASON

1. INTRODUCTION

Estimates are presented for the number of tropical cyclones (NTC), the number of hurricanes

(NH), the number of major hurricanes (NMH), and the number of United States (U.S.) land-falling

hurricanes (NUSLFH) expected for the North Atlantic basin during the 2010 hurricane season (June

1–November 30). The estimates are determined from long-term seasonal averages (1950–2009), the

averages during the current high-activity interval (1995–present), the “usual” behavior of the first

differences in the 10-yr moving averages (10-yma) of the parameters, correlations using 10-yma

parametric values against 10-yma values of surface-air temperature at the Armagh Observatory in

Northern Ireland, and a determination of the probable El Niño (EN) Southern Oscillation (ENSO)

condition expected to prevail during the 2010 hurricane season (i.e., the likelihood of it being either

ENSO-neutral or one of the extremes, EN or La Niña (LN)). The estimates are also compared

against seasonal estimates recently given (December 2009) by the Colorado State University (CSU)

team1 and the Tropical Storm Risk (TSR) team2 (United Kingdom). The official National Oceanic

and Atmospheric Administration (NOAA) forecast is made each May, just prior to the start of hurricane season. The present work represents a continuation of nearly 2 decades of climate-related

research performed at Marshall.3–20 (The reader is reminded that a tropical cyclone is a “warm-core,

nonfrontal, synoptic-scale cyclone that originates over tropical or subtropical waters, with organized

deep convection and a closed surface wind circulation about a well-defined center” that has a sustained peak wind speed (PWS) ≥ 34 kt;21 a hurricane is a tropical cyclone with sustained PWS ≥ 64 kt;

and a major hurricane is a tropical cyclone with sustained PWS ≥ 96 kt.)
2. RESULTS AND DISCUSSION

2.1 Statistical Aspects of the North Atlantic Basin Tropical Cyclones (1950–2009)

Figure 1 displays the yearly (seasonal) frequencies of (a) NTC, (b) NH, (c) NMH, and (d)

NUSLFH for the 60-yr interval 1950–2009 as observed for the North Atlantic basin. The thin-jagged lines are the yearly observed counts and the thick-smoothed lines are the 10-yma values, which

indicate the current trend. The horizontal lines represent the long-term means. The mean, standard

deviation (sd) and range appear to the right in each panel, as do the individual yearly frequency distributions. On average, one finds that about 11 tropical cyclones form in the North Atlantic basin

during any given hurricane season (648 over the 60-yr interval), spanning a range of 4 to 28 and having an sd = 4. The fewest number (4) formed in 1983 and the most (28) formed in 2005. Examination

of the yearly frequency distribution indicates that 32 of 60 seasons (53%) had a yearly frequency of

NTC = 8–12 per year, 16 of 60 seasons (27%) had a yearly frequency of NTC > 12 per year, and 12

of 60 seasons (20%) had a yearly frequency NTC < 8 per year. Since 1995, only 3 seasons (20%) have

had a frequency of NTC < 11 per year, including the years 1997 (8), 2006 (10), and 2009 (9), all ENrelated years.

For NH (fig. 1b), on average, one finds that about 6 hurricanes form in the North Atlantic

basin during any given hurricane season (374 over the 60-yr interval), spanning a range of 2 to 15

and having an sd = 2.6. The fewest number (2) formed in 1982 and the most (15) formed in 2005.

Examination of the yearly frequency distribution indicates that 34 of 60 seasons (57%) had a yearly

frequency of NH = 4–7 per year, 17 of 60 seasons (28%) had a yearly frequency of NH > 7 per year,

and 9 of 60 seasons (15%) had a yearly frequency of NH < 4 per year. Since 1995, only two seasons

(13%) have had a yearly frequency of NH < 4 per year, including the years 1997 (three) and 2009

(three), again, both being EN-related years.

For NMH (fig. 1c), on average, one finds that about 2–3 major hurricanes form in the North

Atlantic basin during any given hurricane season (161 over the 60-yr interval), spanning a range

of 0 to 8 and having an sd = 1.9. The fewest number (zero) has occurred four times, in the years

1968, 1972, 1986, and 1994, while the most (eight) have occurred only once, in 1950. Examination

of the yearly frequency distribution indicates that 32 of 60 seasons (53%) had a yearly frequency

of NMH = 1–2 per year, 24 of 60 seasons (40%) had a yearly frequency of NMH > 2 per year, and

4 of 60 seasons (7%) never had a major hurricane, including the years 1968, 1972, 1986, and 1994,

as mentioned above, all being EN-related years except 1968. Since 1995, there have been no years

in which a major hurricane has not formed in the North Atlantic basin, with all years, except 1997,

having a yearly frequency of NMH ≥ 2 per year.

For NUSLFH (fig. 1d), on average, one finds that about 1–2 hurricanes strike the U.S. coastline

during any given hurricane season (95 over the 60-yr interval), spanning a range of 0 to 6 and having

an sd = 1.5. The fewest number (0) has occurred 12 times (in the years 1951, 1962, 1973, 1978, 1981,

2
mean = 10.8

sd = 4.0

range = 4–2

30

25

20

15

10

5

30

25

20

z 15

10

5

(a)

15

10

xz

5

(b)

10

x

z 5

(c)

10

x

w 5

M

(d) 1950 1960 1970 1980 1990 2000

Year

0

10 5 0

Frequency

15

10

mean = 6.2

z

x

sd = 2.6 5

range = 2–15

0

10 5 0

Frequency

10

mean = 2.7 5 3

sd = 1.9 x

range = 0–8

^ 0

20

Frequency 010

mean =1.6

zc

5

sd = 1.5 =

range = 0–6 0

2010

50 0

Frequency

Figure 1. Yearly frequencies of (a) NTC, (b) NH, (c) NMH, and (d) NUSLFH

for the North Atlantic basin (1950–2009).

1982, 1990, 1994, 2000, 2001, 2006, and 2009), while the most (6) have occurred only 3 times (in the

years 1985, 2004, and 2005). The years 1951, 1982, 1994, 2006, and 2009 were EN-related years, while

the years 1962, 1973, and 2000 were LN-related years. Examination of the yearly frequency distribution indicates that 38 of 60 seasons (63%) had no more than one land-falling hurricane to strike the

U.S. coastline. Since 1995, there have been 8 years when the NUSLFH exceeded one per year and

5 years when the NUSLFH was three or more per year, with only the years 2000, 2001, 2006, and

2009 having no U.S. land-falling hurricanes

3
An interesting aspect of the yearly frequencies, true in particular for NMH, is that there is

the hint of a strong decadal signal imbedded in the yearly frequencies with numbers being greater

(more active) in the 1950s to the mid-1960s and again from the mid-1990s to the present and lesser

(less active) between the mid-1960s and the mid-1990s. For the first more active interval, 1950–1965,

the mean (± 1 sd) for each of the parameters measures 9.6 ± 2.6, 6.3 ± 2.3, 3.6 ± 2.2, and 1.8 ± 1.2,

respectively. For the second more active interval, 1995–2009, the mean (± 1 sd) for each of the parameters measures 14.5 ± 4.7, 7.8 ± 3.2, 3.7 ± 1.8, and 2 ± 2, respectively. Statistical testing (the t-test for

independent samples) reveals that the difference in means for NTC is highly statistically significant, 22

indicating that the present second more active interval has seen a greater number of tropical cyclones

forming in the North Atlantic basin than in the former first more active interval (an increase of about

50%). While true, statistical testing also reveals that the difference in means for NH, NMH, and

NUSLFH is not statistically important between the two perceived more active intervals. Therefore,

while the number of tropical cyclones forming in the North Atlantic basin has increased over time,

there appears to have been no statistically significant increase in the number of hurricanes, major

hurricanes, or U.S. land-falling hurricanes when comparing the two more active intervals; however,

increases of 20%, 3%, and 10%, respectively, have occurred. (One speculates that the significant difference in NTC between the two more active intervals might merely reflect better observations today

as compared to the past, owing to the use of satellites.)

For the less active interval (1966–1994), the mean (± 1 sd) for each of the parameters measures 9.6 ± 3, 5.4 ± 2.1, 1.6 ± 1. 1, and 1.3 ± 1.3, respectively. Statistical testing, comparing this less

active interval with the first more active interval, reveals that the difference in means for NTC is not

statistically important nor is it statistically important for NH or NUSLFH. However, the difference

in means is highly statistically significant for NMH. Comparison of this less active interval with

the current more active interval reveals that the difference in means is statistically important for all

parameters except NUSLFH. Hence, on the basis of NMH, there appears a highly statistically significant difference in the means between the less active and the more active intervals, indicating that

the current more active interval is more than twice as active as the less active interval. For NTC, the

current interval is more than 50% more active than the less active interval; for NH, the current active

interval is more than 40% more active than the less active interval; and for NUSLFH, the current

more active interval is about 50% more active than the less active interval, although this difference is

not statistically important.

Since the less active interval lasted approximately 3 decades in length, presuming that the

transitioning from more-to-less-to-more active states is quasi-periodic in nature, one speculates that

the current more active interval likely will persist for another 1–2 decades. However, if the current

more active interval is now being driven by increased temperature due to climatic change, then the

current active state might persist longer.

2.2 First Differences of parametric 10-yma values

A simple means for estimating the expected NTC, NH, NMH, and NUSLFH for the 2010

hurricane season can easily be accomplished by examining the “usual” behavior of their 10-yma

values (from one year to the next). Figure 2 plots the first differences of the 10-yma values (fd (x) 10,

where x is the parameter of interest) for (a) NTC, (b) NH, (c) NMH, and (d) NUSLFH. For NTC

4
fd(NMH) 10

o

c ^

o I o

cr

oμ

^ T

v

oUL r

Lo

Cl)

fd(NUSLFH) 10

0

Lq

o °

cr

0

o T W

v ^

a

N LL z

bCIA M Sy

l

C

z

U

CD

CD H+-I

CD zN U

z

0

o

0

co

0

o

U rn ^

i~

b

i~

CD

co

C N

t•.

w

fd(NTC) 10fd(NH)10

5
(fig. 2a), the first difference in its 10-yma values between 2003 and 2004 is zero. The distribution of

first difference values (shown to the right in each panel) reveals that a first difference of ± 0.1 is the

“usual” value, occurring 27 out of 54 years (50%). For 9 of 54 years (17%), the first difference has

measured –0.4 to –0.2, and for 18 of 54 years (33%), the first difference has measured ≥ 0.2, with the

largest first difference (0.9) occurring in 1999. Presuming that the first difference of the 10-yma values for NTC will fall within the “usual” range, one estimates the 10-yma value of NTC for 2005 to be

15.3 ± 0. 1, further suggesting that the yearly value of NTC for 2010 should be about 19 ± 2 (i.e., 19 ± 2

= 20(15.3 ± 0.1) – 2(136) – 15, where 136 represents the sum of NTC for the interval 2001–2009 and 15

is the NTC for 2000). Past behavior indicates that the proportion of first differences equal to ± 0.1 is

50%, suggesting that there is about a 50% chance that NTC for 2010 will be 19 ± 2; there is about a

67% chance that NTC for 2010 will be 21 or fewer and about an 83% chance that NTC for 2010 will

be 17 or more. (The reader should note that a larger positive first difference indicates a higher NTC

for the upcoming hurricane season, while a smaller or more negative first difference indicates a lower

NTC for the upcoming hurricane season.)

Similarly, one can compute the “usual” current trend values of the 10-yma values for the

other parameters and estimate their expected levels of activity for the 2010 hurricane season. Such an

analysis suggests that the 10-yma value of NH for 2005 will be about 7.9 ± 0. 1, thereby yielding the

estimate for 2010 of NH = 14 ± 2 (57% chance), NH ≤ 16 (72% chance), and NH ≥ 12 (85% chance).

For NMH, its 10-yma value for 2005 is expected to be about 3.8 ± 0. 1, thereby yielding the estimate

for 2010 of NMH = 7 ± 2 (65% chance), NMH ≤ 9 (81% chance), and NMH ≥ 5 (83% chance). For

NUSLFH, its 10-yma value for 2005 is expected to be about 2.1 ± 0. 1, thereby yielding the estimate

for 2010 of NUSLFH = 4 ± 2 (78% chance), NUSLFH ≤ 6 (91% chance), and NUSLFH ≥ 2 (87%

chance).

2.3 Armagh Observatory (Northern Ireland) Surface-Air Temperature

and Correlations Against It Based on 10-yma values

Figure 3a displays the yearly means of surface-air temperature (in °C) at Armagh Observatory in Northern Ireland (<AT>) for the interval 1950–2009, plotted as the thin -jagged line, and

its 10-yma values, plotted as the thick-smoothed line. Figure 3b shows the variation of the first

difference in the 10-yma values of <AT>. For the 60-yr interval 1950–2009, <AT> has averaged

9.47 °C, spanning a range of 8.35 to 10.59 °C and has an sd = 0.52 °C. Ten-year moving average values of <AT> are found to decrease between the mid-1950s and about 1982, then to increase thereafter, somewhat loosely reminiscent of the behaviors of NTC, NH, NMH, and NUSLFH plotted

in figure 1. Since 1995, all yearly values of <AT> have exceeded its long-term mean except for the

year 1996, and the yearly value for 2007 is the highest surface-air mean temperature ever recorded at

Armagh Observatory since the beginning of its calibrated continuous record in 1844. (Temperature

measurements actually extend from 1796 at Armagh Observatory but have been calibrated only since

1844. 23–25)

First differences of the 10-yma values of <AT> are broadly distributed, with 40 of 54 years

(74%) having a “usual” first difference of ± 0.05 °C. Presuming such behavior to continue, one expects

the 10-yma value for <AT> in 2005 to be about 10.1 ± 0.05 °C, thereby, yielding an expected yearly

surface-air temperature at Armagh Observatory in 2010 to be about <AT> = 10.33 ± 1 °C, with any

value exceeding 10.59 °C being a new record high temperature at Armagh Observatory.

6
fd(<AT>)

10

^n o

° o °o 0 0

0 0 0 o I I

0

v

c

as

Q

as

0

7
Figure 4 depicts the scatter plots and inferred regressions of the 10-yma values of (a) NTC,

(b) NH, (c) NMH, and (d) NUSLFH against <AT> for the present more active interval 1995–2004

(y 1) and the overall interval 1950–2004 (y2). All inferred regressions show that, during either the present more active interval or the overall interval, a direct correlation between the parametric values

and <AT> is hinted at, one that suggests increased frequencies as temperature increases. However, a

radical departure of the inferred regression using only the more recent values (y 1

) in comparison to

the inferred regression using all available values (y2) is apparent (i.e., the inferred regression for the

more recent values has a much steeper slope than the inferred regression using all available values).

This behavior is found to be true for all correlations. It is interesting that the branch of values above

the regressions and to the left (denoted y3), in particular for NMH, represents values for the first

more active interval (1950–1965), while the flat horizontal branch (averaging about 1.8) that connects

the two more active branches represents the values for the less active interval (which has considerable overlap with the second more active interval beginning about 1985). The inferred slopes for the

two more active interval regressions are numerically similar, 3.2 for the first more active interval and

2.9 for the second more active interval. The primary difference between the two more active interval

regressions is that the present one has shifted about 0.5 °C warmer with respect to the earlier more

active interval regression. Such behavior suggests that the Earth’s chaotic climate system demonstrates hysteresis on decadal time scales.

Table 1 summarizes separately the inferred regression equations for NTC, NH, NMH, and

NUSLFH against <AT> based on 10-yma values for both the present more active interval 1995–

2004 and the overall interval 1950–2004. All regressions are inferred to be statistically important

(at a > 99.9% confidence level ( cl)). For the present more active interval, the inferred regression for

NTC against <AT> has a coefficient of correlation (r) = 0.988 and a coefficient of determination

(r2) = 0.977, meaning that nearly 98% of the variance in the 10-yma values of NTC (since 1995) can

be explained simply by the variation of the 10-yma values of <AT> alone. Instead, for the larger

overall interval, the inferred regression for NTC against <AT> has a slightly smaller r and r2 , inferring that only about 79% of the variance in NTC can be explained by the variation in <AT> alone.

Similar findings are found for the other parameters, with the present more active interval having

inferred regressions of larger r and r2 as compared to inferred regressions for the overall interval.

Presuming the 10-yma value of <AT> for 2005 to be 10.1 ± 0.05 °C from the “usual” behavior of its first difference in 10-yma values (i.e., a first difference of ± 0.05 °C having occurred about

74% of the time, as discussed above), one infers the 10-yma value of NTC for 2005 to be about

15.06 ± 0.5, based on the fit for the present more active interval 1995–2004, which further suggests

a yearly frequency of NTC = 14 ± 10 for 2010. Instead, based on the overall interval 1950–2004,

one expects the 10-yma of NTC for 2005 to be only about 13.86 ± 0.25, which is unrealistic since

such a value implies a negative yearly frequency for NTC in 2010. Based on the overall interval fit,

to have an average yearly frequency (NTC = 11) for 2010, the 10-yma value of NTC for 2005 must

equal 14.9, which in turn means that the 10-yma value of <AT> for 2005 would need to be about

10.12 °C (based on the fit of <AT> against NTC). However, such a value suggests that the yearly

mean surface-air temperature at Armagh Observatory for 2010 would be about 10.73 °C or 0.14 °C

warmer than its previous record high temperature of 10.59 °C in 2007 and 0.9 °C warmer than the

yearly mean surface-air temperature of 9.83 °C in 2009.

8
y 1

y2

20

15

e

v

z

10

(a) 5

10

7.5

e

= 5

z

2.5

(b)

5

e

37 2.5

z

(c)

5

e

x

2.5

z

(d) 8.5 9.0 9.5 10.0 10.5

<AT>10

Figure 4. Scatter plots of the 10-yma values of (a) NTC, (b) NH, (c) NMH,

and (d) NUSLFH against 10-yma values of <AT>.

9
Table 1. Correlations of NTC, NH, NMH, and NUSLFH versus <AT> using 10-yma

values for the intervals 1995–2004 and 1950–2004.

1995–2004 1950–2004

Regression Equation r r

2

se Regression Equation r r

2

se

NTC = –87.54+10.158<AT> 0.988 0.977 0.16 NTC = –37.57+5.092<AT> 0.891 0.794 0.81

NH = –32.51 + 4.017<AT> 0.967 0.935 0.24 NH = –16.41 +2.388<AT> 0.827 0.684 0.47

NMH = –25.41+2.895<AT> 0.937 0.878 0.17 NMH = –14.57+1.817<AT> 0.621 0.386 0.69

NUSLFH = –22.82+2.476<AT> 1 0.927 0.859 1 0.16 1 NUSLFH = –4.12+0.605<AT> 1 0.491 0.241 1 0.31

Similarly, presuming the 10-yma value of <AT> for 2005 to be 10.1 ± 0.05 °C, the 10-yma

value of NH for 2005 is found to be about 8.06 ± 0.2, using the present more active interval fit, and

about 7.71 ± 0.12, using the overall interval fit; the 10-yma value of NMH for 2005 using the two

fits is found to be about 3.83 ± 0.14 and 3.78 ± 0.09, respectively; and the 10-yma value of NUSLFH

for 2005 using the two fits is found to be about 2.19 ± 0.12 and 1.99 ± 0.03, respectively. Based on

these projected 10-yma parametric values, one expects yearly values for 2010 using the two fits to be

about NH = 17 ± 4 or 10 ± 3, respectively; NMH = 8 ± 2 or 7 ± 1, respectively; and NUSLFH = 6 ± 2 or

2 ± 2, respectively. Obviously, a higher mean surface-air temperature in 2010 at the Armagh Observatory would suggest a greater yearly frequency of tropical cyclone formation in the North Atlantic

basin, while a lower mean surface-air temperature would suggest a lower yearly frequency of tropical

cyclone formation (for all categories of tropical cyclones).

2.4 Comparison of Armagh Observatory (Northern Ireland) Surface-Air Temperatures and Mauna

Loa Carbon Dioxide Atmospheric Concentration Measurements Based on 10-yma values

Recently, it was shown that surface-air temperature, as measured at the Armagh Observatory,

Northern Ireland, is strongly related to the atmospheric concentration of carbon dioxide (CO 2,) as

measured at Mauna Loa, Hawaii, particularly since about 1982. 20 Armagh Observatory lies about

1 km northeast of the center of the ancient city of Armagh, Northern Ireland, being located at

latitude 54°21'12'' N and longitude 6°38'54'' W and situated about 64 m above sea level at the top

of a small hill in an estate of natural woodland and parkland that measures about 7 ha. Continuous calibrated daily measurements of the minimum and maximum temperature have been made

there since 1844. On the other hand, the Mauna Loa Observatory is located in a barren lava field

of an active volcano located at latitude 19°32' N and longitude 155°35 W at an elevation of

3,397 m above sea level. The Mauna Loa measurements represent the longest continuous record

of atmospheric CO2 concentration measurements available for study, 26 having begun in 1958.

Figure 5 shows the yearly variation of the 10-yma of the Mauna Loa CO2 (MLCO2) atmospheric concentration (in ppmv) for the data-available interval 1963–2004. The 41-yr record of

10-yma values of MLCO2 plainly shows that the atmospheric concentration of CO2, as measured at

Mauna Loa, has increased continuously with the passage of time from about 319 ppmv in 1963 to

nearly 378 ppmv in 2004, an increase of slightly more than 18%. Furthermore, the rate of growth in

the 10-yma values of MLCO2 is found to exceed that of a simple linear increase, being more reflective of an exponential rise. Hence, higher concentrations appear more likely to occur sooner rather

than later, especially if the rise in CO 2 atmospheric concentration continues unabated.

10
1970 1980 1990 2000

380

370

360

330

320

310

1960

350

340

Year

Figure 5. 10-yma values of MLCO2.

11
In figure 5, individual linear fits are shown as the straight lines for each decadal set of observations (1960–1969, 1970–1979, etc.). The 10-yma values of MLCO2 within each decadal set are

found to essentially lie along these individual decadal linear fits. Extension of the most recent linear

fit (2000–2004) to 2005 (the filled square) suggests that the 10-yma value of the MLCO 2 concentration will be about 379.4 ppmv.

Figure 6 displays the scatter plot of 10-yma values of <AT> against 10-yma values of MLCO2.

The individual dots represent specific years, which are observed to move progressively from the lower

left to the upper right with the passage of time. For convenience, calendar years are identified at

5-year intervals to guide the reader.

10.5

y = –1.358 + 0.031 x

r =0.987, r

2 = 0.974

se = 0. 04, cl >99.9% 2000

10-yma <MLCO2> (2005) = 379.4 =10-yma <AT> (2005) = 10.27± 0.10

10.0 1995

A

a

V

E

CM 1985

9.5 1970

1965 1975 1980 i

1990 •

9.0

310 320 330 340 350 360 370 380

10-yma <MLCO2>

Figure 6. Scatter plot of 10-yma values of <AT> against 10-yma values of MLCO2.

Prior to about 1982, 10-yma values of <AT> do not appear to correlate strongly with 10-yma

values of MLCO2, as indicated by the horizontal straight line through the individual yearly values

(1963–1982). However, from about 1982 onwards (an interval of 24 years), a very strong correlation

is inferred to exist between 10-yma values of <AT> and MLCO 2, one having r = 0.987, indicating

that more than 97% of the variance in the 10-yma values of <AT> can be explained by the variation of the 10-yma values of MLCO 2 . The variation about the inferred linear regression line, while

having a standard error of estimate (se) = 0.04 °C, appears to range (i.e., maximal extremes) by about

± 0.1 °C, indicating a spread of about ± 2.5 se. Using the estimated value of 379.4 ppmv for the

10-yma value of MLCO2 for 2005 (from figure 5), one infers that the 10-yma value of <AT> should

be about 10.27 ± 0.1 °C for 2005, which, if true, indicates that the first difference for the 10-yma value

of <AT> for 2005 will be about 0.17 ± 0.1 °C, a value outside and high of the “usual” first difference

expected range (± 0.05 °C). Recall from figure 3b that 9 of 54 years (17%) have had first differences in

12
the 10-yma values of <AT> ≥ 0.07 °C, with no year, as yet, having a first difference that exceeded 0.13

°C. However, the indication from the <AT> –MLCO2

 relationship (fig. 6) is that the first difference

in 10-yma values of <AT> will be ≥ 0.07 °C and possibly as high as 0.27 °C, implying that the 10-yma

value of <AT> for 2005 should be ≥ 10.17 °C, a new record high at Armagh Observatory, if true.

However, a 10-yma value of <AT> for 2005 ≥ 10.17 °C presents a difficult quandary in that

it would suggest a yearly temperature <AT> ≥ 11.73 °C at Armagh Observatory in 2010, a value well

above the record high temperature of 10.59 °C in 2007. Furthermore, such a value would indicate a

year-to-year change in yearly temperature from 2009 to 2010 ≥ 1.9 °C. Large year-to-year temperature

excursions ≥ 1.5 °C in absolute value occasionally have been seen at Armagh Observatory, but never

has there been one as large or larger than 1.9 °C. For example, the yearly temperature at Armagh

dropped 1.54 °C between 1815 and 1816, very probably due to the eruption of Tambora in April

1815.27 Also, the yearly temperature dropped 1.54 °C between 1878 and 1879, possibly related to the

eruption of Cotopaxi in June 1877,26 and an unexplained drop of 1.7 °C occurred between 1921 and

1922. In contrast, an unexplained rise of 1.56 °C occurred between 1892 and 1893, unexplained in

that there is no apparent ENSO event28 or cataclysmic volcanic eruption26 occurring around these

dates. Therefore, while large year-to-year fluctuations in temperature at Armagh Observatory have

occurred, they have occurred only rarely, with none having been seen since 1921–1922 and none

being larger than 1.7 °C.

Should a large-year-to-year temperature rise ≥ 1.9 °C actually occur between 2009 and 2010,

one would expect yearly parametric frequencies possibly far greater in 2010 than has ever been seen

before. As noted above, a rise of 1.9 °C to 11.73 °C in 2010 yields a 10-yma of 10.17 °C in 2005 for

<AT>. Using this value in the inferred regressions given in table 1, one can deduce 10-yma values

for the parameters for 2005, which in turn can provide estimates for the yearly frequencies for 2010.

For NTC, such an analysis yields 10-yma values from y 1 and y2 for 2005 of 15.77 and 14.22, respectively, suggesting a yearly frequency for 2010 of NTC = 28 and 0 (actually, –3, which is unrealistic),

respectively; for NH, one obtains 10-yma values for 2005 of 8.34 and 7.88, respectively, suggesting

a yearly frequency for 2010 of NH = 23 and 14, respectively; for NMH, one obtains 10-yma values

for 2005 of 4.03 and 3.9 1, respectively, suggesting a yearly frequency for 2010 of NMH = 12 and 9,

respectively; and for NUSLFH, one obtains values for 2005 of 2.36 and 2.03, respectively, suggesting a yearly frequency for 2010 of NUSLFH = 9 and 3, respectively. Since there is no known reason

not to use the inferred regressions for the now occurring more active interval (y 1

), one which plainly

suggests that the Earth’s climate system has undergone recent change and that tropical cyclone formation in the North Atlantic basin is now responding directly to the effects of enhanced warming

more strongly than in previous years, it is surmised that increased activity during the 2010 hurricane

season should be expected with, perhaps, as many as 28 NTC, 23 NH, 12 NMH, and 9 NUSLFH

possibly being seen (these estimates are considered upper limits). Such expected frequencies, should

they truly occur, represent record to near record yearly frequencies for the North Atlantic basin.

However, if the current ongoing EN event, which had its onset in June 2009, persists through 2010,

a sharp reduction in the expected yearly parametric frequencies for 2010 might occur.29–32

13
2.5 El Niño Southern Oscillation Cycle Effects

Today, the Oceanic Niño Index (ONI) is often used to determine the state of the ENSO

cycle. The ONI represents the 3-month running mean (also called the 2-mma) of the ERSST.v3b

sea surface temperature (SST) anomalies in the Niño 3.4 region (5 ° N–5° S and 120–170° W) relative to the 1971–2000 base period. 33 An EN is said to be occurring when the ONI ≥ 0.5 °C for five or

more consecutive months. When 0.5 °C ≤ ONI < 1 °C, the EN is described as being of “weak” (W)

strength; when 1 °C ≤ ONI < 1.5 °C, the EN is described as being of “moderate” (M) strength; and

when ONI ≥ 1.5 °C, the EN is described as being of “strong” (S) strength. The current ongoing EN

is now classified as an S event, having had an apparent ONI maximum value of 1.8 °C in December

2009 (ONI slightly decreased to 1.7 °C in January 2010). Similarly, an LN is said to be occurring

when the ONI ≤ –0.5 °C for five or more consecutive months. When –1 °C ≤ ONI < –0.5 °C, the LN

is described as being of W strength; when –1.5 °C ≤ ONI < –1 °C, the LN is described as being of M

strength; and when ONI < –1.5 °C, the LN is described as being of S strength. All other times, when

the ONI fails to meet the definition of EN or LN, the ENSO cycle is said to reflect ENSO-neutral

conditions.

On the basis of ONI, there have been 31 ENSO extreme events for the interval 1950–2009,

including 18 EN and 13 LN events. For convenience, these 31 events are identified in table 2, giving

their start, peak, and end dates; duration in months (from start to end); max ONI; mean ONI over

the duration of the event (<<ONI>>); event type; event strength; and the sums of NTC, NH, NMH,

and NUSLFH that formed during the event (between event start and end). Averages of the specific

parameters appear at the bottom but they exclude the first LN event, which had an onset prior to

January 1950, and the last EN event, which remains an ongoing event. Hence, of the 18 EN events,

5 have been W events, 4 have been M events, and 9 have been S events. For the 17 EN events with

complete coverage, the average duration is 10.1 months; the average max ONI is 1.4 °C; the average

<<ONI>> is 0.97 °C; and the average NTC, NH, NMH, and NUSLFH during an EN event is 8, 4.4,

1.5, and 1, respectively.

The EN event of longest duration (19 months) occurred August 1986–February 1988, having

multiple peaks in February 1987 (1.3 °C), August 1987 (1.6 °C), and September 1987 (1.6 °C). The

EN event of largest anomaly (max ONI = 2.5 °C) occurred May 1997–May 1998, and this event also

had the largest <<ONI>> (1.74 °C). The W EN event of June 2004–February 2005 had the largest

sums of NTC (15), NH (9), NMH (6), and NUSLFH (6). Weak EN events average about 6 months

in duration, having a range of 5 to 9 months, and average about 9, 6, 2.4, and 0.4 for NTC, NH,

NMH, and NUSLFH, respectively, during their operative lives. Moderate EN events average about

8 months in duration, having a range of 6 to 11 months, and average about 5.8, 3.8, 1, and 0.3 for

NTC, NH, NMH, and NUSLFH, respectively, during their operative lives. Strong EN events average about 13.6 months in duration, having a range of 11 to 19 months, and average about 8.5, 3.6,

1.3, and 1 for NTC, NH, NMH, and NUSLFH, respectively, during their operative lives. Plainly, as

the strength of the EN anomalous event increases, there is a tendency for its duration to increase in

length and tropical cyclone activity to be suppressed, this is particularly true for NH, NMH, and

NUSLFH.

14
Table 2. Listing of EN and LN events based on ONI (ERSST.v3b).

EN and LN Events Sums

Dur Event

Start Peak End (mo) max ONI <<ONI>> Type Strength NTC NH NMH NUSLFH

B01-1950 01-1950(?) 03-1951 >15 –1.7(?) – LN S 13 11 8 3

08-1951 10-1951 12-1951 5 0.8 0.7 EN W 9 7 4 0

04-1954 11-1955a 01-1957 34 –2 –0.98 LN S 31 21 10 9

04-1957 01-1958 06-1958 15 1.7 0.99 EN S 9 3 2 1

09-1962 11-1962* 01-1963 5 –0.7 –0.62 LN W 3 2 1 0

07-1963 11-1963* 01-1964 7 1 0.86 EN M 9 7 2 1

04-1964 10-1964* 01-1965 10 –1.2 –0.93 LN M 12 6 6 4

06-1965 11-1965 04-1966 11 1.6 1.12 EN S 6 4 1 1

12-1967 02-1968 04-1968 5 –0.9 –0.72 LN W 0 0 0 0

11-1968 01-1969* 06-1969 8 1 0.79 EN M 0 0 0 0

09-1969 11-1969 01-1970 5 0.8 0.66 EN W 12 8 2 1

07-1970 01-1971 *b 01-1972 19 –1.3 –0.91 LN M 22 10 3 4

05-1972 12-1972 03-1973 11 2.1 1.32 EN S 7 3 0 1

05-1973 12-1973c 05-1976 37 –2.1 –1.11 LN S 29 14 6 2

09-1976 11-1976 02-1977 6 0.8 0.63 EN W 3 2 0 0

09-1977 11-1977a 01-1978 5 0.7 0.64 EN W 6 4 0 1

05-1982 12-1982* 06-1983 14 2.3 1.39 EN S 6 2 1 0

10-1984 12-1984 09-1985 12 –1.1 –0.71 LN M 11 8 2 4

08-1986 08-1987*d 02-1988 19 1.6 1.11 EN S 11 6 1 2

05-1988 11-1988* 05-1989 13 –1.9 –1.29 LN S 12 6 3 1

05-1991 01-1992e 07-1992 15 1.8 1.13 EN S 9 4 2 1

05-1994 12-1994 03-1995 11 1.3 0.83 EN M 7 3 0 0

09-1995 11-1995f 03-1996 7 –0.7 –0.63 LN W 7 5 3 1

05-1997 11-1997* 05-1998 13 2.5 1.74 EN S 8 3 1 1

07-1998 12-1999* 06-2000 24 –1.6 –1.03 LN S 26 18 8 6

10-2000 12-2000 02-2001 5 –0.7 –0.58 LN W 4 1 0 0

05-2002 11-2002 03-2003 11 1.5 1.03 EN S 12 4 2 1

06-2004 09-2004 02-2005 9 0.9 0.72 EN W 15 9 6 6

08-2006 11-2006* 01-2007 6 1.1 0.83 EN M 7 5 2 0

09-2007 01-2008* 05-2008 9 –1.4 –1.04 LN M 13 6 2 1

06-2009 1 12-2009 – >8 1.8 – EN S (9) (3) (2) (0)

Averages: EN 10.1# 1.4# 0.97# 8# 4.4# 1.5# 1#

LN 15@ –1.3@ –0.88@ 14.2@ 1 8.1@ 3.7@ 2.7@

Note: B means before.

? means uncertain.

* means the month shown and the following month.

a means the month shown and the two following months.

b means multiple peaks: –0.9 in September and November 1970, –1.3 in January and February 1971, and –1 in November 1971.

c means multiple peaks: –2.1 in December 1973, –1.1 in April 1974, –0.9 in November 1974, and –1.7 in November and December 1975.

d means multiple peaks: 1.3 in February 1987 and 1.6 in August and September 1987.

e means multiple peaks:1 in July 1991 and 1.8 in January 1992.

f means the month shown and the following 3 months.

# means excludes 06–2009 event.

@ means excludes B01 –1950 event.

15
In contrast, of the 13 LN events, 4 have been W events, 4 have been M events, and 5 have

been S events. For the 12 LN events with complete coverage, the average duration is 15 months; the

average max ONI is –1.3 °C; the average <<ONI>> is –0.88 °C; and the average NTC, NH, NMH,

and NUSLFH during an LN event is 14.2, 8.1, 3.7, and 2.7, respectively. The LN event of longest duration (37 months) occurred May 1973–May 1976, having multiple peaks in December 1973

(–2.1 °C), April 1974 (–1.1 °C), November 1974 (–0.9 °C), November 1975 (–1.7 °C), and December 1975

(–1.7  ̊C). The LN event of largest anomaly (max ONI = –2.1 °C) occurred May 1973–May 1976. The

LN event of largest <<ONI>> (–1.29 °C) occurred May 1988–May 1989. The LN event of largest

NTC (31), NH (21), NMH (10), and NUSLFH (9) occurred April 1954–January 1957. Weak LN

events average about 5.5 months in duration, having a range of 5 to 7 months, and average about 3.5,

2, 1, and 0.3 for NTC, NH, NMH, and NUSLFH, respectively, during their operative lives. Moderate LN events average about 12.5 months in duration, having a range of 9 to 19 months, and average

about 14.5, 7.5, 3.3, and 3.3 for NTC, NH, NMH, and NUSLFH, respectively, during their operative

lives. Strong LN events average about 27 months in duration, having a range of 13 to 37 months, and

average about 24.5, 14.8, 6.8, and 4.5 for NTC, NH, NMH, and NUSLFH, respectively, during their

operative lives. Plainly, as the strength of the LN anomalous event increases, there is a tendency for

its duration to increase in length and tropical cyclone activity to be enhanced.

Table 3 shows the frequency distribution (by calendar month) of the onset, peak, and end

dates for EN and LN events. Both EN and LN events have always had their onsets after the month

of March, with June being the most prominent month of onset for an EN event (there is no prominent onset month for an LN event). Fourteen of the 17 EN events with complete coverage had their

primary peak in November–January, and 10 of the 12 LN events with complete coverage had their

primary peak also in November–January. Hence, 24 of the 29 ENSO extreme events (82.8%) had

their peak temperature anomalous excursion, as determined by the ONI, in November–January. For

both EN and LN events, the end of the event tends to occur during January–June, just before the

Table 3. Frequency distribution of onset, peak, and end dates for EN and LN events.

Onset Peak End

Month EN LN EN LN EN LN

01 3 2 4 4

02 1 3 1

03 3 2

04 1 2 1 1

05 6 2 1 3

06 3 3 1

07 1 2 1

08 3 1

09 3 3 1 1

10 2 1 1

11 1 8 4

12 1 1 1 1 3 1 4 1

16
official start of the hurricane season. This is true for 15 of 17 EN events (88.2%) and 11 of 12 LN

events (91.7%), respectively.

Figure 7 shows the temporal variation of the annual mean ONI (<ONI>) values (fig. 7a)

and the first difference of the 10-yma annual mean ONI values (fig. 7b), plotted similarly to that of

figure 3. <ONI> is merely the 12-month average of the monthly ONI values. While yearly values of

<ONI> are found to vary randomly about the value of <ONI> = 0 °C, the behavior of the 10-yma

values of <ONI> (the thick smoothed line) suggests that <ONI> values tended to be negative prior

to about 1980 and positive thereafter. Presently (in 2004, the last available 10-yma of <ONI>), the

10-yma value of <ONI> = 0.03, and the current trend of the 10-yma values of <ONI> appears, at

least to the eye, to possibly be tracking downward, which, if true, suggests that it might soon become

negative in value. From the “usual” first difference, one finds that 33 of 49 years (67%) have had a

first difference in the 10-yma value of <ONI> = ±0.05 °C. Hence, one expects the 10-yma value of

<ONI> for 2005 to be about 0.03 ± 0.05 °C if the “usual” first difference occurs again for 2004. Such

a value implies a yearly value of <ONI> for 2010 of –2.2 ± 1 °C (or ≤ –1.2 °C).

Negative values of yearly <ONI> are indicative of ENSO-neutral to LN-like conditions in

the ENSO cycle, while positive values of yearly <ONI> are indicative of ENSO-neutral to EN-like

conditions in the ENSO cycle. Because the yearly <ONI> value for 2010 is expected to be negative

(≤ –1.2 °C) from the “usual” behavior of the first difference in the 10-yma values of <ONI>, one

infers that the present ongoing EN that began in mid-2009 might soon end and be replaced by an

LN event of M-to-S strength sometime during the 2010 hurricane season. If true (remember, the

reliability of the prediction is dependent solely upon whether the first difference in the 10-yma of

<ONI> will, indeed, be ± 0.05 °C), then the activity level in the North Atlantic basin during the 2010

hurricane season should be expected to be higher than average.

The reader should note that there is only a 15% chance that the first difference in the 10-yma

value of <ONI> for 2004 will be of value 0.06 °C or warmer, and it has exceeded 0.09 °C only once.

For the 2010 value of <ONI> to be ≥ 0 °C, the 10-yma value of <ONI> for 2005 would have to measure 0.14 °C or warmer, meaning that the first difference in the 10-yma value of <ONI> for 2004

would have to be 0.11 °C or higher, something that has happened only once (0.15 °C in 1960.)

Table 4 gives the number of EN months (NENM), the number of LN months (NLNM), and

the number of ENSO-neutral months (NNM) separately for negative and positive <ONI> yearly

values for the interval 1950–2009 (720 months). Negative and positive <ONI> values are observed

to have occurred equally, 360 months each. Of the 360 months when <ONI> was negative in value,

178 were classified NLNM, 167 were classified NNM and only 15 were classified NENM. Thus,

when the yearly <ONI> value is negative, there is only about a 4% chance that the year contained

any EN-related months, a 46% chance that it contained ENSO-neutral-related months, and a 49%

chance that it contained LN-related months. When the yearly <ONI> value is positive, there is only

about a 5% chance that the year contained any LN-related months, a 50% chance that it contained

ENSO-neutral-related months, and a 45% chance that it contained EN-related months. For the interval 1950–2009, NENM has occurred about 25% of the time, NLNM has occurred about 27% of the

time, and NNM has occurred about 48% of the time.

17
18

fd(<ONI>)

10

^n o U') o 0

CD 0 0 0 0 0 0 0 0 o I I I

i

j j j

A

V

C

d

7

Q

dULL

0
Table 4. Comparison of <ONI> and NLNM, NNM, and NENM.

ENSO Category Negative <ONI> Positive <ONI> Totals

NLNM 178 17 195

NNM 167 180 347

NENM 15 163 178

Total 360 360 720

Table 5 gives the distribution of NLNM/yr, NNM/yr, and NENM/yr for specific ranges of

<ONI> yearly values. The table is comprised of three sections, with table 5a giving the results for

NLNM/yr, table 5b giving the results for NNM/yr, and table 5c giving the results for NENM/yr. As

an example, there have been 4 years when <ONI> measured in the range –1.49 to –1 °C, with all

4 years being associated with LN events and all having NLNM = 12 during those years. When <ONI>

measures –1.49 to –0.5 °C, one finds LN-related months to have occurred about 81% of the time,

ENSO-neutral-related months to have occurred about 16% of the time, and EN-related months to

have occurred only about 3% of the time. Hence, when <ONI> is –0.5 °C or cooler, one can confidently say that the hurricane season probably is LN-related, since 13 of 15 years had 8 or more LNrelated months during the year and 15 of 15 years had 5 or more LN-related months during the year.

Similarly, when <ONI> measures 0.5 °C or warmer, one finds EN-related months to have

occurred about 68% of the time, ENSO-neutral-related months to have occurred about 30% of the

time, and LN-related months to have occurred only about 2% of the time. Hence, when <ONI> is

0.5 °C or warmer, one expects the hurricane season to be EN-related, since 13 of 13 years had 6 or

more EN-related months during the year when <ONI> was 0.5 °C or warmer.

The difficulty in determining whether a particular hurricane season might be LN-related or

EN-related and, thus, possibly affecting the expected activity levels for the hurricane season occurs

when <ONI> = –0.49 to 0.49 °C. Thirty-two of 60 years have had <ONI> within this range. Of the

32 years (384 months), LN-related months were observed about 12% of the time (6 or fewer months

of the year), ENSO-neutral-related months were observed about 71% of the time, and EN-related

months were observed about 17% of the time (7 or fewer months of the year). Hence, when <ONI>

falls within the range of –0.49 to 0.49 °C, it is highly likely that the year will be classified as ENSOneutral; however, there remains about a one in eight chance that an LN event might overlap the hurricane season and about a one in six chance that an EN event might overlap the hurricane season.

2.6 The Relationship Between the Annual Mean Oceanic Niño Index and

the Annual Mean Surface-Air Temperature at Armagh Observatory

Figure 8 displays the scatter plot of <ONI> against <AT> using 10-yma values for the interval 1955–2004. The thin vertical and horizontal lines represent the median values for the 10-yma

values of <AT> and <ONI>, respectively. The diagonal line running from lower left to upper right

represents the inferred regression based on linear regression analysis. Ten-year moving average values of <ONI> are observed to range between –0.29 °C (in 1971) and 0.32 °C (in 1994), while 10-yma

values of <AT> are observed to range between 9.05 °C (in 1982) and 10.13 °C (in 2002 and 2003).

19
Table 5. Distribution of (a) NLNM/yr, (b) NNM/yr, and (c) NENM/yr

versus <ONI> yearly value.

a. NLNM/yr versus <ONI> yearly value

<ONI> Yearly Value

NLNM/yr –1.49 to –1 –0.99 to –0.5 –0.49 to 0 0 to 0.49 0.5 to 0.99 1 to 1.49 Total

0 0 0 6 13 8 2 29

1 0 0 1 1 3 0 5

2 0 0 1 0 0 0 1

3 0 0 2 1 0 0 3

4 0 0 3 1 0 0 4

5 0 2 1 0 0 0 3

6 0 0 1 1 0 0 2

7 0 0 0 0 0 0 0

8 0 2 0 0 0 0 2

9 0 4 0 0 0 0 4

10 0 0 0 0 0 0 0

11 0 0 0 0 0 0 0

12 4 3 0 0 0 0 7

Total 4 11 15 17 11 2 60

b. NNM/yr versus <ONI> yearly value

<ONI> Yearly Value

NLNM/yr –1.49 to –1 –0.99 to –0.5 –0.49 to 0 0 to 0.49 0.5 to 0.99 1 to 1.49 Total

0 4 3 0 0 0 1 8

1 0 1 0 1 0 0 2

2 0 2 0 0 2 0 4

3 0 3 1 0 1 0 5

4 0 0 0 1 5 1 7

5 0 0 1 3 2 0 6

6 0 0 1 2 1 0 4

7 0 2 1 2 0 0 5

8 0 0 1 1 0 0 2

9 0 0 2 1 0 0 3

10 0 0 1 1 0 0 2

11 0 0 2 0 0 0 2

12 0 0 5 5 0 0 10

Total 4 11 15 17 11 2 60

c. NENM/yr versus <ONI> yearly value

<ONI> Yearly Value

NLNM/yr –1.49 to –1 –0.99 to –0.5 –0.49 to 0 0 to 0.49 0.5 to 0.99 1 to 1.49 Total

0 4 8 10 5 0 0 27

1 0 1 3 0 0 0 4

2 0 1 1 1 0 0 3

3 0 1 0 2 0 0 3

4 0 0 1 1 0 0 2

5 0 0 0 4 0 0 4

6 0 0 0 3 1 0 4

7 0 0 0 1 3 0 4

8 0 0 0 0 5 1 6

9 0 0 0 0 1 0 1

10 0 0 0 0 1 0 1

11 0 0 0 0 0 0 0

12 0 0 0 0 0 1 1

Total 4 11 15 17 11 2 60

20
The results of Fisher’s exact test for 2×2 contingency tables appears at the bottom, 34 yielding the

probability (P) of obtaining the observed result, or one more suggestive of a departure from independence (chance), to be 0.2%. Similarly, one infers that the regression is statistically significant at

cl >99.9%. Hence, given an expected value for the 10-yma of <AT> for 2005, one can estimate the

expected 10-yma value of <ONI> for 2005, which can then be used to estimate the yearly value of

<ONI> for 2010 for a determination of the likelihood that 2010 will be either LN-related, ENSOneutral-related, or EN-related.

From the “usual” behavior of the first difference of the 10-yma values of <AT>, as has

previously been shown, one expects a 10-yma value of <AT> for 2005 to be about 10.1 ± 0.05 °C

(fig. 3). However, from the expected value of the 10-yma of MLCO2 for 2005 (379.4 ppmv in figure

5), one expects the 10-yma value of <AT> for 2005 to be about 10.27 ± 0.1°C (fig. 6). Averaging the

two estimates yields the “best guess” 10-yma value of <AT> to be about 10.19 ± 0.08 °C for 2005.

Presuming that the 10-yma value of <AT> for 2005 will, indeed, be 10.19 °C, from the linear regression (fig. 8) one infers the 10-yma value of <ONI> to be about 0.18 °C for 2005, which

implies that the first difference of the 10-yma value of <ONI> would be 0.15 °C for 2005, well

outside and high of its “usual” first difference value (± 0.05 °C) and tying the record set in 1960.

A 10-yma value of <ONI> equal to 0.18 °C means that the <ONI> yearly value for 2010 would be

0.8 °C, which further suggests that the 2009 EN event very likely would continue into the 2010 hurricane season, in contrast to that presented earlier, which had presumed a downward trend in the

10-yma values of <ONI>.

Another reason for possibly accepting <ONI> as being positive in value for 2010 is that the

2009 EN is now known to be classified as an S event. Recall that S EN events average about 14 months

in length and have persisted as long as 19 months in length (range 11 to 9 months), as shown in

table 2 for the 1986 EN event. Because the 2009 EN has, thus far, persisted only 8 months, through

January 2010, it likely will continue for several more months. A fit of EN duration versus max ONI,

not shown, suggests that the 2009 EN, having a max ONI of 1.8 °C (in December 2009), should

have a duration (± 1 se) measuring about 12 ± 3 months. Hence, the 2009 EN should end sometime

between March and September 2010. However, if it turns out to be a multiyear event, it could persist through 2010 and not end until early 2011. Previously, there have been five multiyear EN events

(where a multiyear EN event is one having a duration longer than 12 months), including EN events

in 1957, 1982, 1986, 1991, and 1997. The 2009 EN event ranks as the fourth strongest EN event since

1950, tied with the 1991 EN event in terms of max ONI.

The behavior of the 10-yma of <AT> certainly suggests a far different scenario for <ONI>

in 2010 than the one based on the “usual” behavior of the first difference of the 10-yma value of

<ONI>. Recall that the “usual” behavior of the 10-yma of <ONI> suggests that the 2009 EN event

should end in early 2010 (before June) and be replaced by an M-to-S LN event in the latter portion of

2010. Also, from table 4 it was shown that a positive value of <ONI> tends to be indicative of a year

that is classified ENSO-neutral-related or EN-related, while a negative value of <ONI> tends to be

indicative of a year that is classified ENSO-neutral-related or LN-related. Obviously, the first several

months of 2010 should prove instructive for determining whether the 2010 hurricane season might

21
9.5 10.0 10.5

O

A

E 0.0 0V

–0.5

–1.0

–1.5

9.0

1.5

1.0

0.5

Y

<AT>1 0

Figure 8. Scatter plot of 10-yma values of <ONI> against 10-yma values of <AT>.

be expected to be ENSO-neutral or associated with an ENSO extreme event (either a continuing EN

event or the occurrence of an LN event).

2.7 predicting Yearly <ONI> From the January–May Average and prediction

of Warmest and Coolest Monthly ONI value

Figure 9 compares the <ONI> yearly value against the average ONI value for the 5-month

interval January–May. The average ONI value for January–May appears to provide a fairly strong

indication as to whether the year as a whole would be expected to be either of positive or negative

value. When the average <ONI> value for January–May is positive, the <ONI> yearly value also is

expected to be positive in value, as indicated by the inferred regression line (y) and the distribution of

positive values, which has been true for 22 of 30 years. Likewise, when the January–May average is

22
0 0.0

V

–0.5

–1.0

–1.5

1%

1.5

1.0

0.5

n

–1.5 –1.0 –0.5 0.0 0.5 1.0 1.5

ONI (J–M)

Figure 9. Scatter plot of <ONI> against the January–May average value of ONI.

negative, the <ONI> yearly value also is expected to be negative, as indicated by the inferred regression and the distribution of negative values, which has been true for 23 of 30 years. Furthermore,

when the January–May value is ≥ 0.5 °C, 9 of 11 times this previously has indicated that the <ONI>

yearly value was, indeed, positive, and 4 of 11 times it indicated that it too was ≥ 0.5 °C; whereas,

when the January–May value is ≤ –0.5 °C, 13 of 13 times this previously has indicated that the <ONI>

yearly value was negative and 11 of 13 times it also indicated an <ONI> yearly value ≤–0.5 °C. (In

figure 9, the inferred regression line marked x plots the ONI 5-month averages against the <ONI>

yearly value, so that, given an expected <ONI> yearly value, one might gauge the expected ONI average for the first 5 months of the year.)

23
From above, based on the expected value of the 10-yma of <AT> for 2005 (10.19 °C) and the

inferred relationship between 10-yma values of <ONI> and <AT>, one expects the <ONI> yearly

value for 2010 to be about 0.8 °C. If true, then the first 5-month average of ONI for 2010 should

be about 0.58 ± 0.52 °C (± 1 se), indicating that the 2009 EN event probably is slowly decreasing in

strength towards ENSO-neutral conditions later in the year. The preferential relationship shown in

figure 9 has failed in 15 of 60 years, so there remains a 1 in 4 chance that it might also fail in 2010, as

well. The NOAA Climate Prediction Center continues to predict the persistence of the 2009 EN, at

least, through the spring of 2010. 35

Figure 10 compares (a) the warmest monthly ONI and (b) the coolest monthly ONI with the

<ONI> yearly value. Accepting 0.8 °C as the 2010 <ONI> yearly value, one infers that the warmest

monthly ONI should be about 1.6 ± 0.5 °C (± 1 se) and the coolest monthly ONI should be about

0 ± 0.4 °C (± 1 se) for 2010. (In January 2010, the ONI monthly value measured 1.7 °C.)

2.8 predicting the 2005 10-yma values for NTC, NH, NMH, and NUSLFH From the Expected

10-yma values of <AT> and <ONI> and the Yearly Frequencies for 2010

Table 6 gives the observed and predicted 10-yma parametric values for the interval 1995–2004,

using a single-variate fit based on the 10-yma value of <AT> and a bivariate fit based on 10-yma

values of both <AT> and <ONI>. For comparison, the mean and sd values of the parameters for

the interval 1995–2004 are also given. The use of the bivariate fits does not appear to substantially

improve the predictions as compared to using the single-variate fit based on <AT> alone.

Table 7 provides the 2005 10-yma value predictions for NTC, NH, NMH, and NUSLFH

based on the mean statistical behavior (1995–2004), the single-variate fit (using <AT> alone), and the

bivariate fit (using both <AT> and <ONI>, where the latter fits use the “usual” expected values and

the “best guess” values). For all parameters, values higher than their statistical means are indicated.

For NTC, the 2005 10-yma value is estimated to be about 15.5 ± 0.5; for NH, the 2005 10-yma value is

estimated to be about 8.2 ± 0.3; for NMH, the 2005 10-yma value is estimated to be about 4 ± 0.2; and

for NUSLFH, the 2005 10-yma value is estimated to be about 2.4 ± 0.2. From these 10-yma values,

one can estimate the 2010 parametric yearly values. For NTC, NH, NMH, and NUSLFH, the 2010

expected frequencies are 26 ± 10, 20 ± 6, 11 ± 4, and 10 ± 4, respectively. Therefore, the techniques as

employed here suggest that the 2010 North Atlantic basin hurricane season will be an above average

season in terms of activity, having NTC ≥ 16, NH ≥ 14, NMH ≥ 7, and NUSLFH ≥ 6.

2.9 Comparison With Colorado State University and Tropical Storm Risk Estimates

The early CSU team estimate calls for the 2010 North Atlantic basin hurricane season to be

somewhat more active than the long-term statistical means, 1 this estimate being more typical of the

current active phase (since 1995). In particular, the CSU team estimates 11–16 tropical cyclones, 6–8

hurricanes, and 3–5 major hurricanes during the 2010 hurricane season. They also estimate the likelihood of a U.S. land-falling hurricane to be above average during the 2010 hurricane season.

24
3.0 x

x = –0.417 + 0.586y

2.5 r = 0.822, r

2 = 0.675

se = 0.359, cl >99.9% •

y

2.0

z 1.5

C

Tr

0 1.0

d

0.5 y =0.708 + 1.153x

r = 0.822, r

2 = 0.675

• se = 0.504, cl >99.9%

0.0 •

• 23 24

⇒ P <0.1%

–0.5 •

–1.0

(a)

1.0 x •

x = 0.506 + 0.729y

r = 0.812, r

2 = 0.659 y

0.5 - se =0.368, cl >99.9%

C 0.0

r

•

Co

–0.5

d

o

..

•

v0

–1.0

•

y = –0.698 + 0.904x

r = 0.812, r

2 = 0.659

' se = 0.410, cl >99.9%

–1.5

•

MO5

⇒ P <0.1%

•

–2.0 - •

(b)

•

–1.5 –1.0 –0.5 0.0 0.5 1.0 1.5

<ONI>

Figure 10. Scatter plot of (a) the warmest and (b) the coolest monthly ONI value against

the yearly mean <ONI>.

25
Table 6. Observed and predicted 10-yma parametric values for 1995–2004.

Observed* Predicted (<AT>)** Predicted (<AT>, <ONI>)***

Year NTC NH NMH NUSLFH NTC NH NMH NUSLFH NTC NH NMH NUSLFH

1995 11.1 6.4 2.6 1.4 11.4 6.6 2.8 1.3 11.3 6.6 2.8 1.4

1996 11.5 6.7 2.8 1.4 11.5 6.7 2.8 1.3 11.6 6.7 2.8 1.3

1997 12.1 6.9 3 1.3 11.9 6.8 2.9 1.4 12 6.8 2.9 1.3

1998 12.7 7.1 3.1 1.4 12.7 7.1 3.2 1.6 12.8 7.2 3.2 1.6

1999 13.5 7.5 3.5 1.7 13.5 7.5 3.4 1.8 13.5 7.5 3.4 1.8

2000 14.4 8 3.9 2.2 14 7.7 3.5 1.9 14 7.7 3.5 2

2001 14.7 8 3.8 2.3 14.6 7.9 3.7 2.1 14.5 7.9 3.7 2.2

2002 14.9 8 3.7 2.2 15.4 8.2 3.9 2.3 15.3 8.2 3.9 2.3

2003 15.3 8.2 3.8 2.2 15.4 8.2 3.9 2.3 15.5 8.2 3.9 2.1

2004 1 15.3 1 7.9 1 3.8 1 2.1 1 15.1 1 8.1 1 3.8 1 2.2 1 15.1 1 8.1 1 3.8 1 2.1

* NTC: mean = 13.55, sd =1.599

NH: mean = 7.47, sd = 0.646

NMH: mean = 3.4, sd = 0.481

NUSLFH: mean = 1.82, sd = 0.416

** Single variate fits: NTC =–87.541 +10.158<AT>, r= 0.988, se =0.207

NH =–32.51 +4.017<AT>, r= 0.967, se = 0.238

NMH =–25.411 +2.895<AT>, r= 0.937, se = 0.177

NUSLFH =–22.818+2.476<AT>, r= 0.927, se =0.143

*** Bivariate fits: NTC =–80.297+9.452<AT> – 2.027<ONI>, r= 0.99, se =0.255

NH =–30.631 +3.834<AT> – 0.513<ONI>, r= 0.962, se= 0.2

NMH =–24.95+2.85<AT> – 0.118<ONI>, r= 0.94, se =0.186

NUSLFH =–29.327+3.109<AT>+ 1.913<ONI>, r= 0.954, se = 0.142

Table 7. Predictions of 10-yma parametric values for 2005 based on the interval 1995–2004.

FIT NTC NH NMH NUSLFH

Mean (±sd): 13.5±1.6 7.5±0.7 3.4±0.5 1.8±0.4

Single Variate:(“usual” behavior <AT> = 10.1 ±0.05) 15.1 ±0.5 8.1 ±0.2 3.8±0.2 2.2±0.1

Single Variate:(“bestguess” <AT> = 10.19±0.08) 16 ±0.8 8.4±0.3 4.1±0.2 2.4±0.2

Bivariate:(“usual” behaviors <AT> = 10.1 ±0.05, <ONI> = 0.03±0.05) 15.1 ±0.4 8.1 ±0.1 3.8±0.2 2.1 ±0.3

Bivariate:(“bestguess” <AT> = 10.19±0.08,<ONI> = 0.18±0.15) 15.7±0.4 1 8.3±0.3 1 4.1±0.2 1 2.7±0.5

Similarly, the TSR team estimate calls for the 2010 North Atlantic basin hurricane season

to also be more active than the long-term statistical mean. 2 In particular, the TSR team projects an

increase of 35% above average in numbers of tropical cyclones and U.S. land-falling hurricanes for

the 2010 season, with a 62% likelihood that the 2010 season will be in the upper one-third of active

years. The TSR team predicts about 13.9 ± 4.9 tropical storms, 7.4 ± 3.1 hurricanes, and 3.4 ± 1.8

major hurricanes.

As previously noted, the techniques employed in this study indicate increased activity in the

North Atlantic basin during the 2010 hurricane season, in agreement with the early forecasts of the

CSU and TSR teams. It is anticipated that the 2010 season will have seasonal frequencies for all

26
categories of tropical cyclones above their statistical means, both long-term means and means for

the current more active interval (which began in 1995). This is attributed primarily to an expected

rise in surface-air temperature at the Armagh Observatory due to the continued increase of the

atmospheric concentration of CO2 . For the 2010 North Atlantic basin hurricane season, one expects

NTC = 14.5 ± 4.7, NH = 7.8 ± 3.2, NMH = 3.7 ± 1.8, and NUSLFH = 2 ± 2, based on the means

(± 1sd) for the current more active interval (1995–2009); NTC = 19 ± 2, NH = 14 ± 2, NMH = 7 ± 2,

and NUSLFH = 4 ± 2, based on the “usual” behavior of the first differences; and NTC ≥ 16, NH ≥ 14,

NMH ≥ 7, and NUSLFH ≥ 6, based on the expected average ranges from the preferential single-variate and bivariate fits. Until additional information becomes available, it seems highly likely that the

2010 North Atlantic basin hurricane season will be considerably more active, especially in comparison to that experienced in the 2009 hurricane season. However, should the 2009 EN event persist

through 2010 and have an additional peak in late 2010 or early 2011, a reduction in the seasonal

estimates might be required.

2.10 predicting the Next El Niño Southern Oscillation Extreme Event Occurrence

Recently, it was shown that there exists a statistically significant association between the recurrence period (RP) and duration of EN events of M-to-S strength, 19 where the RP is determined from

the start date of the event of known duration. Figure 11 displays the scatter plot of RP versus duration. In figure 11, filled circles identify W events, filled squares identify M events, and filled triangles

identify S events. The inferred regression (y) is determined using only EN events of M-to-S strength

and has r = 0.681, se = 14 months, and cl > 98%. Thus, given the duration of an M-to-S EN event, one

can crudely estimate the likelihood of the occurrence of the next EN event.

150

EN Events (Start–Start)

Moderate–Strong Events:

y = 2.616 + 3.323x

r = 0.681, r2 = 0.463 2 8

100 se = 13.964, cl >98%⇒ P =1.3%

6 1 1

0E V

•

50

•

•

•

n

5 10 15

Duration (mo)

Figure 11. Scatter plot of RP against duration for EN events.

20

27
LN Events

150

100

0

E

a

50

5 10 15 20 25 30 35 40

Similarly, based on the Fisher’s exact test for 2×2 contingency tables, the observed distribution, or one more suggestive of a departure from independence, is computed to be only P = 1.3% for

EN events. Six of 9 W and M EN events are observed to be located in the lower left quadrant (duration < 11 months and RP < 36 months), while 7 of 8 S EN events populate the upper right quadrant

(duration ≥ 11 months and RP ≥ 36 months). Because the 2009 EN event is of S strength, statistically

speaking, one expects its duration to be ≥ 11 months and to have an associated RP ≥ 36 months, indicating that one should not expect another EN event until June 2012 or later.

While there appears to be a loose statistical association between RP and duration for EN

events, no such statistically important relationship is found for LN events. Figure 12 shows the scatter plot of RP against the duration for LN events, plotted similarly to that of figure 11. Obviously,

RP for LN events is independent of the duration and strength of the preceding LN event.

Duration (mo)

Figure 12. Scatter plot of RP against duration for LN events.

28
3. SUMMARY

This present work marks a continuation of studies of the Earth’s climate system as related to

the prediction of hurricane activity for the North Atlantic basin. The record of hurricane activity

is considered reliable only since about 1950, owing to the routine use of aircraft reconnaissance and

continuous satellite viewing (since the 1960s). 36 On average, about 11 tropical cyclones have formed

in the North Atlantic basin during the hurricane season since 1950, spanning a range of 4 to 28, with

the fewest occurring in 1983 and the most in 2005; on average, about 6 hurricanes have formed in the

North Atlantic basin during the hurricane season, spanning a range of 2 to 15, with the fewest occurring in 1982 and the most in 2005; and, on average, about 2–3 major hurricanes have formed in the

North Atlantic basin, spanning a range of 0 to 8, with no major hurricanes having occurred in 1968,

1972, 1986, and 1994 and the most occurring, thus far, only in 1950. The years of lowest frequency

have always been associated with the occurrences of EN events, while the highest frequencies have

always been associated with years having no occurrences of EN events.

Concerning land-falling hurricanes that strike the U.S. Gulf coast and eastern seaboard, on

average, this has occurred about 1–2 times per year, spanning a range of 0 to 6. The fewest number have occurred 12 times (including years 1951, 1962, 1973, 1978, 1981, 1982, 1990, 2000, 2001,

2006, and 2009) with nearly half of these years being associated with EN events, and the most have

occurred only 3 times (including years 1985, 2004, and 2005).

On the basis of the 10-yma behavior of the frequency of major hurricanes, it is apparent that

the activity level in the North Atlantic basin varies on decadal timescales, with greater activity having been seen prior to 1966 and again after 1994 and lesser activity of about three decades length

separating the two more active states. For the first more active interval (prior to 1966), the averages

(± 1 sd) of NTC, NH, NMH, and NUSLFH are found to be about 9.6 ± 2.6, 6.3 ± 2.3, 3.6 ± 2.2, and

1.8 ± 1.2, respectively, and for the second more active interval (1995–present) to be about 14.5 ± 4.7,

7.8 ± 3.2, 3.7 ± 1.8, and 2 ± 2, respectively. Statistical testing reveals that, while there is no statistically

important difference in the means for the two more active intervals for NH, NMH, and NUSLFH,

the difference in means is statistically important for NTC. Also, compared to the less active interval,

which has respective averages of about 9.6 ± 3, 5.4 ± 2.1, 1.6 ± 1. 1, and 1.3 ± 1.3, the present more

active interval has parametric means that are all significantly different, except for NUSLFH. Hence,

there has been a significant increase in the frequency of tropical cyclone formation in the North

Atlantic basin, one that manifests itself for all categories of tropical cyclones with the exception of

U.S. land-falling hurricanes (when the comparison is between the current more active interval and

the preceding less active interval).

First differences in the 10-yma values of the parameters are useful in that they provide reasonable estimates for the expected frequencies of tropical cyclones for an upcoming season, estimates

based on the “usual” statistical behavior of their distributions (current trends). For the 2010 North

Atlantic basin hurricane season, the “usual” behavior of their first differences in 10-yma values suggests NTC, NH, NMH, and NUSLFH to be about 19 ± 2 (50% chance), 14 ± 2 (57% chance), 7 ± 2

29
(65% chance), and 4 ± 2 (78% chance), respectively. The chances of exceeding the lower estimates are

83% (≥ 17), 85% (≥ 12), 83% (≥ 5), and 87% (≥ 2), respectively.

The 10-yma seasonal frequency of tropical cyclone formation in the North Atlantic basin is

found to strongly associate with the 10-yma of surface-air temperature as recorded at the Armagh

Observatory in Northern Ireland, particularly during the current more active interval. 15–18 Statistically important regressions, having r ≥ 0.93, are inferred to exist between the 10-yma values of NTC,

NH, NMH, and NUSLFH and 10-yma values of <AT> for the interval 1995–2004. Based on the

“usual” behavior of the first differences of the 10-yma values of <AT>, one expects the 2005 10-yma

value for <AT> to be about 10.1 ± 0.05 °C (74% chance), which suggests 10-yma values for 2005

of NTC = 15.06 ± 0.5, NH = 8.06 ± 0.2, NMH = 3.83 ± 0.14, and NUSLFH = 2.19 ± 0.12. Such values

imply 2010 frequencies to be 14 ± 10, 17 ± 4, 8 ± 2, and 6 ± 2, respectively. Also, a 2005 10-yma of

<AT> = 10.1 °C implies that the 2010 <AT> yearly temperature would measure 10.73 °C, which, if

true, represents a new record high temperature at Armagh, one that exceeds the previous record high

of 10.59 °C in 2007.

Now, the 10-yma value of <AT> is known to track the 10-yma of the CO2 atmospheric concentration as measured at the Mauna Loa Observatory in Hawaii fairly closely ( r = 0.987),20 particularly since about 1982. Carbon dioxide appears to be increasing exponentially from about 319 ppmv

in 1963 to 378 ppmv in 2004, based on 10-yma MLCO2 values. Projecting forward 1 year suggests

that the 10-yma value of MLCO2 will measure about 379.4 ppmv in 2005, which further suggests

that the 10-yma value of <AT> will measure about 10.27 ± 0.1 °C in 2005. However, such a value

presents a difficult quandary in that it implies an <AT> yearly temperature ≥11.73 °C in 2010, a

value more than 4 sd higher than the 1950–2009 average. Presuming the 10-yma of <AT> = 10.17 °C

(the lower limit) in 2005, one expects NTC = 28, NH = 23, NMH = 12, and NUSLFH = 9 in the 2010

hurricane season, all record highs or near-record highs.

Instead, using a “best guess” for the 10-yma of <AT> (= 10.19 °C), achieved by averaging

the “usual” first difference current trend value (10.1 °C) and the expected value from the <AT>-

MLCO2 inferred relationship (10.27 °C), one obtains NTC = 26 ± 10, NH = 20 ± 6, NMH = 11 ± 4,

and NUSLFH = 10 ± 4 for the 2010 hurricane season. From these inferred ranges, one determines

NTC ≥ 16, NH ≥ 14, NMH ≥ 7, and NUSLFH ≥ 6 for the 2010 hurricane season. In comparison to the

CSU and TSR forecasts, the estimates presented here are above their upper limits, with all forecasts

suggesting the 2010 hurricane season to be more active than the 2009 season and more akin to the

averages of the current more active interval that began in 1995.

Whether or not the 2009 EN will be of sufficient duration to inhibit the expected frequencies

of tropical cyclone formation that have been forecast for the 2010 season is an unknown. It is known

that the 2009 EN event is an S event (max ONI = 1.8 °C in December 2009), and S events are known

to persist about 14 months on average (range 11 to 19 months). Through January 2010, the 2009

EN event has persisted 8 months (onset in June 2009). It is anticipated that it will slowly weaken in

strength, perhaps ending sometime between March and September 2010 (usually an EN event ends

in the first half of a year). If the current EN event ends before the 2010 hurricane season, then one

expects the 2010 hurricane season to be ENSO-neutral to LN like and the expected frequencies to be

more akin to the current averages and observed ranges (NTC = 8–28, NH = 3–15, NMH = 1–7, and

30
NUSLFH = 0–6). On the other hand, if the 2009 EN event should persist into the 2010 hurricane

season, then one would expect to see a sharp reduction in the frequencies for the 2010 hurricane

season. About one-third of the EN events since 1950 have been multiyear EN events. These include

the 1957, 1982, 1986, 1991, and 1997 EN events. So, it is possible that the 2009 EN event could also

be a multiyear event, although it certainly is not expected based on the “usual” first difference value

of the 10-yma of <ONI>, which strongly suggests the quick demise of the 2009 EN event in early

2010, being replaced by an M-to-S LN event during the latter portion of the year. On the basis of the

RP-duration preferential association for M-to-S EN events, one does not expect another EN event

to have an onset until June 2012 or later, suggesting that the next two seasons will be ENSO-neutral

to LN like and be more indicative of increased activity.

31

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35
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4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER

An Estimate of the North Atlantic Basin Tropical Cyclone Activity 5b. GRANT NUMBER

for the 2010 Hurricane Season

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Robert M. Wilson

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14. ABSTRACT

Estimates are presented for the tropical cyclone activity expected for the 2010 North Atlantic basin hurricane season.

It is anticipated that the 2010 season will be more active than the 2009 season, reflecting increased frequencies more

akin to that of the current more active phase that has been in vogue since 1995. Averages (± 1 sd) during the current more active phase are 14.5 ± 4.7, 7.8 ± 3.2, 3.7 ± 1.8, and 2 ± 2, respectively, for the number of tropical cyclones

(NTC), the number of hurricanes (NH), the number of major hurricanes (NMH), and the number of United States

(U.S.) land-falling hurricanes (NUSLFH). Based on the “usual” behavior of the 10-yma parametric first differences,

one expects NTC = 19 ± 2, NH = 14 ± 2, NMH = 7 ± 2, and NUSLFH = 4 ± 2 for the 2010 hurricane season; however,

based on the “best guess” 10-yma values of surface-air temperature at the Armagh Observatory (Northern Ireland)

and the Oceanic Niño Index, one expects NTC ≥ 16, NH ≥ 14, NMH ≥ 7, and NUSLFH ≥ 6.

15. SUBJECT TERMS

tropical cyclone activity, North Atlantic basin, 2010 hurricane season, ENSO cycle,

Armagh Observatory, Mauna Loa CO 2

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