Author: Stephen A. Kearney
Mentor: Dr. Matthew Eastin,
Central College

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Two primary components to hurricane forecasting:
- Track
- Intensity
Current research on structure and intensity
Knowledge gained about storm structure with flight level data
(e.g., Jorgensen, 1984)
Do relationships exist between eye size and intensity?
Previous studies (e.g., Weatherford and Gray 1988) show weak correlation between eye size and minimum sea level pressure
(MSLP)

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Temporal changes associated with eye wall replacement cycles also noted (Willoughby et al.
1990; Willoughby et al. 1982; Black et al. 1992)
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Generally, smaller eye sizes coincident with greater intensity
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Project investigates impact of eye diameter asymmetries on intensity changes
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Hypothesis: Eye sizes are characterized by changes in storm intensity

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Procedures
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Investigations
- Direct relationship
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- Intensity change with eye size change
Effect of eye symmetry on storm intensity

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88 total flights analyzed, only at hurricane strength
Flights analyzed at 850 mb and 700 mb levels
14 various N. Atlantic hurricanes from 1979 through 1995
Included some notable storms:
Gilbert, 1988; Andrew, 1992

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Flights composed of several legs, or passes through eye
RMW = Radius of Maximum Wind (Shea et al. 1973)
- Value of eye size
Two values for mean RMW
RMW
1
RMW
2
= Average of RMW from first four legs
= Average of RMW from last four legs
Only flights with at least eight legs used

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Mean times found in same way as mean RMW.
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Labeled t
1 and t
2
, respectively
Change in Mean RMW per second
Mean RMW = RMW
2
Change t
2
– RMW
1
– t
1

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Calculated change in Maximum Wind (m/s) and change in MSLP (mb)
Change values covered separate six-hour periods during and after each flight
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- Immediate or future impact?
RMW Standard Deviation (RMW SD) found separately for RMW-1 and RMW-2

Direct relationship
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Initial Max Wind to RMW
1
Final Max Wind to RMW
2
Initial MSLP to RMW
1
Final MSLP to RMW
2

130.00
120.00
110.00
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
30
130.00
120.00
110.00
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
30 40 50 60
Initial Max Wind (m/s)
70 80 40 50 60 70
Final Max Wind (m/s)
80 90
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Any direct relationship between RMW and Max Wind?

130.00
120.00
110.00
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
875
130.00
120.00
110.00
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
875
900 925 950
Initial MSLP (mb)
975 1000
900 925 950
Final MSLP (mb)
975 1000
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Any direct relationship between RMW and MSLP?
Very low pressures with small RMW values (Gilbert, 888 mb)

Intensity change relationship with eye change
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Max Wind Change during flight
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Max Wind Change after flight
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MSLP Change during flight
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MSLP Change after flight

20
10
0
-10
-20
-30
-40
-50
50
40
30
100
90
80
70
60
-15
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Any immediate effect on
Max Wind?
Little to no correlation found
Statistics: y = 2.496 - 1.095 x
R=0.039804
-10 -5 0 5
Max Wind Change (m/s)
10 15

100
90
80
70
60
50
10
0
-10
-20
-30
-40
-50
40
30
20
-20 -15 -10 -5 0 5
Post Flight Max Wind Change (m/s)
10
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Any future effect on Max
Wind?
Little to no correlation found
Statistics: y = 1.888 - 0.298 x
R= 0.003811

100
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
-40
-50
-30 -25 -20 -15 -10 -5 0 5 10 15 20
MSLP Change (mb)
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Any immediate effect on
MSLP?
Little to no correlation found
Statistics: y = 2.722 + 0.602 x
R= 0.034097

0
-10
-20
30
20
10
-30
-40
-50
100
90
80
70
60
50
40
-20
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Any future effect on
MSLP Change?
Little to no correlation found
Statistics: y = 1.534 + 0.392 x
R=0.01604
-10 0 10 20
MSLP Change (mb)
30 40

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Direct Relationship
Very little correlation present
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Relationship to RMW Change
Not much correlation
Agrees with findings of Weatherford and Gray
(1988)

Approximate measure of eye structure symmetry
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Larger RMW SD: RMW values dissimilar
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Indicated more asymmetric eye structure
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Smaller RMW SD: RMW values similar
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Indicated more symmetric eye structure

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MSLP and RMW SD had noticeable correlation
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Found ranges of RMW SD to get different
“levels” of eye symmetry (i.e., < 3, 3 to 6, 6 to
9)
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Calculated Mean and Std Dev of MSLP Change within each RMW SD range

MSLP Change vs RMW
1
10 10
SD During Flight
8 8
6 6
4 4
2
0
-2
-10
-12
-4
-6
-8
< 3 3 to 6 6 to 10 10 to 21
RMW-1 Std Dev Range
> 21
2
0
-2
-4
-6
-8
-10
-12
0.00
10.00
20.00
30.00
40.00
RMW-1 Std Dev.
50.00
60.00
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Std Dev bars on left - Variability of MSLP Change
Diagonal lines indicate mean MSLP in each “level”
MSLP change values plotted on right against RMW
1
SD

6
5
4
3
8
7
2
1
0
-1
-2
-3
-8
-9
-10
-4
-5
-6
-7
-11
-12
-13
MSLP Change vs RMW
2
SD During Flight
8
6
4
< 3 3 to 5 5 to 8 8 to 20
RMW-2 Std Dev Range
> 20
2
0
-2
-4
-10
-12
-6
-8
-14
0.00
5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00
RMW-2 Std Dev.
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Std Dev bars on left - Variability of MSLP Change
Diagonal lines indicate mean MSLP in each “level”
MSLP change values plotted on right against RMW
2
SD

-8
-6
-2
-4
0
4
2
10
8
6
14
12
Post Flight MSLP Change vs RMW
1
SD
14
12
10
8
6
4
2
0
-2
-4
-6
-8
-10
0.00
< 3 3 to 6 6 to 9 10 to 21
RMW-1 Std Dev Range
> 21 10.00
20.00
30.00
40.00
RMW-1 Std Dev.
50.00
60.00
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Std Dev bars on left - Variability of MSLP Change
Diagonal lines indicate mean MSLP in each “level”
MSLP change values plotted on right against RMW
1
SD

-6
-8
-10
-2
-4
4
2
0
8
6
10
12
Post Flight MSLP Change vs RMW
2
SD
12
10
8
6
4
2
0
-2
-4
-6
-8
-10
0.00
< 3 3 to 5 5 to 8 8 to 20
RMW-2 Std Dev Range
> 20 10.00
20.00
30.00
RMW-2 Std Dev.
40.00
50.00
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Std Dev bars on left - Variability of MSLP Change
Diagonal lines indicate mean MSLP in each “level”
MSLP change values plotted on right against RMW
2
SD

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Very little relationship between eye diameter and intensity change, current or future
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Symmetric structure indicated by RMW SD
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Lower MSLP Std Dev trended with higher
RMW SD
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MSLP changed the most with more symmetric structure

More asymmetric structure: negative impact on storm
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More time for vertical shear
More time for colder SST’s to inhibit strengthening
More symmetric structure: positive impact on storm
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Allows winds to increase quicker
Other studies (e.g. Shapiro and Willoughby 1982) show more symmetric structure has better “spin-up” effect

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Eye symmetry important to forecasting
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Case study by Willoughby et al. 1990
- Outer eye wall observed to contract before becoming asymmetric
- Retained intensity on one side, then weakened on the other
- Can create different effects on a local area, depending on landfall time and location

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Only flights from 1979 to 1995 were used
Tropical cyclones stronger and more frequent in past ten years
Further studies, especially on 2005 record breaking season, can be done
More frequent flights into storms today
Higher resolution data may indicate further relationships

Author would like to thank the following:
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Dr. Matthew Eastin - mentorship, guidance, and data
Dr. Takle - advice
NOAA’s Hurricane Research Division - data
Classmates and Professors - moral support