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4B.2 A comparison of typhoon best-track data in the western North Pacific: irreconcilable differences.
byMark A. Lander
University of Guam
Central Guam mountains after amajor brushfire.
The two primary agencies responsible for basin-wide TC coverage — the Joint Typhoon Warning Center (JTWC) and the Japan Meteorological Agency (JMA) — are so incompatible as to call into question the utility of their best-track TC data for climate studies.
The Joint Typhoon Warning Center (JTWC), now located in Pearl Harbor, Hawaii, has a nearly 50-year record of tropical storms and typhoons for the western North Pacific Basin. The JTWC is jointly manned by the U.S. Navy and U.S. Air Force to provide tropical cyclone reconnaissance and forecast support to the U.S. Military and other U.S. Government agencies and assets in the eastern Hemisphere. The JTWC has a continuous record of tropical cyclone activity in the western North Pacific extending from 1959 to present. Until the year 2000, it also provided the names for the TCs of that basin.
P. J. Webster, G. J. Holland, J. A. Curry, H.-R. ChangScience 16 September 2005:Vol. 309. no. 5742, pp. 1844 – 1846
Examination of hurricane intensity shows a substantial change in the intensity distribution of hurricanes globally. The number of category 1 hurricanes has remained approximately constant but has decreased monotonically as a percentage of the total number of hurricanes throughout the 35-year period. The trend of the sum of hurricane categories 2 and 3 is small also both in number and percentage. In contrast, hurricanes in the strongest categories (4 + 5) have almost doubled in number (50 per pentad in the 1970s to near 90 per pentad during the past decade) and in proportion (from around 20% to around 35% during the same period). These changes occur in all of the ocean basins.
True if one uses JTWCFalse if one uses JMA !!!
In General:
JTWC intensities too high !!
OR
JMA intensities too low !!
1996 Typhoon Season
-20
-10
0
10
20
30
40
50
60T
D 1
An
nT
D3
Bar
tC
am Dan
Eve
Fra
nk
Glo
ria
Her
bIa
nJo
yL
isa
Kir
kT
D 1
5M
arty
Nik
iO
rso
Pip
erT
D 2
1R
ick
Sal
lyT
S 2
4V
iole
tT
om
Wil
lie
Yat
esZ
ane
Ab
elT
D 3
1B
eth
Car
loT
D 3
4T
S 3
5D
ale
Ern
ieT
S 3
8T
D 3
9T
D 4
0T
D 4
1F
ern
Gre
g
-20
-10
0
10
20
30
40
50
60
1996
V max
JTWC Higher than JMA
JMA No Tropical Warnings
JTWC Lower than JMA
Wind speed difference
(kt)
-40
-30
-20
-10
0
10
20
TD
1A
nn
TD
3B
art
Cam Dan
Eve
Fra
nk
Glo
ria
Her
bIa
nJo
yL
isa
Kir
kT
D 1
5M
arty
Nik
iO
rso
Pip
erT
D 2
1R
ick
Sal
lyT
S 2
4V
iole
tT
om
Wil
lie
Yat
esZ
ane
Ab
elT
D 3
1B
eth
Car
loT
D 3
4T
S 3
5D
ale
Ern
ieT
S 3
8T
D 3
9T
D 4
0T
D 4
1F
ern
Gre
g
-40
-30
-20
-10
0
10
20
JTWC Higher than JMA
JTWC Lower than JMA
1996 Minimum SLPJMA No Tropical Warnings
JTWC = 1.5386 x JMA - 7.8015 1
When intercept not set to zero
1 JTWC = 1.4133 x JMAWhen intercept forced to zero
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120 140 160
JMA Vmax 10-min kts
JTW
C V
max
1-m
in k
ts1996: JTWC Vmax VS JMA Vmax
Why ??
JTWC uses 1-minute average for sustained wind speed.
JMA uses 10-minute average for sustained wind speed.
Difference between 1-min and 10-min is approximately 115%.
Why ??
JTWC and JMA use different T-number conversion tables.
Dvorak T number/wind speed comparison
T Number JTWC JMA 10 to 1 2 30 30 33.6 2.5 35 35 39.2 3 45 45 50.4 3.5 55 55 61.6 4 65 65 72.8 4.5 77 70 78.4 5 90 77 86.2 5.5 102 85 95.2 6 115 93 104.2 6.5 127 100 112.0 7 140 107 119.8 7.5 155 115 128.8 8 170 122 136.6
JMA can’t getCAT 5 until T8 is reached !!
JTWC = 0.00666492523952 (JMA)2 + 0.52216572124655 (JMA) + 7.70018715792769
0
20
40
60
80
100
120
140
160
180
0 20 40 60 80 100 120 140 160 180
JMA 10-Min Vmax
JTW
C 1
-Min
Vm
ax
JTWC VS JMADVORAK T-NUMBER
EQUIVALENT WIND SPEEDS
T 4.0
T 5.0
T 4.5
T 5.5
T 6.0
T 6.5
T 7.0
T 7.5
T 8.0
T 3.5
T 3.0
T 2.5T 2.0
0
20
40
60
80
100
120
140
160
180
2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8T NUMBER
Win
d S
pee
d (
Kts
)
JMA10-Min to 1 Min
JTWC 1-Min
JMA
Who is right ???
Anecdotal Evidence.
Investigate individual TCs
Tropical Storm Greg (43W 96)
Strongest Westerly Wind Burst ever Observed ! (December 1996)
Impacts of TS Greg1996 JTWC Annual TC Report
“Greg was responsible for loss of life and extensive damage to property in the East Malaysian State of Sabah (located on the northwest coast of Borneo). At least 124 lives were reported lost with another reported missing primarily due to flooding from torrential rains. In Kota Kinabalu, The capital of the State of Sabah, high wind scattered billboards and other debris, and broke windows in the 30-story government building.”
Typhoon Vamei
EQ
2 N
4 N
108 E104 E
Singapore
Typhoon Vamei00Z 27 DEC 2001TRMM 85 GHz
Typhoon Vamei. Microwave image courtesy of NRL Monterey:(http://www.nrlmry.navy.mil/tc_pages/tc_home)
JTWC: 75 kt
JMA 45 kt
JTWC Annual Tropical Cyclone report for 2001:
“At 270000Z, JTWC classified the system as a typhoon based on naval ship observations indicating sustained winds within the small eyewall of 75 knots with gusts to 105 knots.”
Even today problems persist.
October 2007: Two midget typhoons
Haiyan
Podul
Midget typhoon Haiyan
JTWC:No Warning.20 kt on ABPW
JMA:40 kt.
TC Podul (Midget Typhoon)
JTWC:No Warning.20 kt on ABPW
JMA: 55 kt
Annual comparisons
Here it gets messy.
1996 Typhoon Season
-20
-10
0
10
20
30
40
50
60T
D 1
An
nT
D3
Bar
tC
am Dan
Eve
Fra
nk
Glo
ria
Her
bIa
nJo
yL
isa
Kir
kT
D 1
5M
arty
Nik
iO
rso
Pip
erT
D 2
1R
ick
Sal
lyT
S 2
4V
iole
tT
om
Wil
lie
Yat
esZ
ane
Ab
elT
D 3
1B
eth
Car
loT
D 3
4T
S 3
5D
ale
Ern
ieT
S 3
8T
D 3
9T
D 4
0T
D 4
1F
ern
Gre
g
-20
-10
0
10
20
30
40
50
60
1996
V max
JTWC Higher than JMA
JMA No Tropical Warnings
JTWC Lower than JMA
Wind speed difference
(kt)
-40
-30
-20
-10
0
10
20
TD
1A
nn
TD
3B
art
Cam Dan
Eve
Fra
nk
Glo
ria
Her
bIa
nJo
yL
isa
Kir
kT
D 1
5M
arty
Nik
iO
rso
Pip
erT
D 2
1R
ick
Sal
lyT
S 2
4V
iole
tT
om
Wil
lie
Yat
esZ
ane
Ab
elT
D 3
1B
eth
Car
loT
D 3
4T
S 3
5D
ale
Ern
ieT
S 3
8T
D 3
9T
D 4
0T
D 4
1F
ern
Gre
g
-40
-30
-20
-10
0
10
20
JTWC Higher than JMA
JTWC Lower than JMA
1996 Minimum SLPJMA No Tropical Warnings
-40
-30
-20
-10
0
10
20T
ess
Vio
la
Win
nie
Ali
ce
Bet
ty
Co
ra
Do
ris
Els
ie
Flo
ssie
Hel
en Ida
Kat
hy
Mar
ie
Ru
by
Sal
ly
Til
da
Vio
let
Wil
da
Cla
ra
Do
t
Ho
pe
Iris
Joan
Kat
e
Lo
uis
e
Op
al
-40
-30
-20
-10
0
10
20
1964
JTWC MSLP Lower than JMA
JTWC MSLP Higher than JMA
Minimum SLP
JMA No Tropical Warnings
JTWC TYPHOONS ONLY
JTWC = 1.5386 x JMA - 7.8015 1
When intercept not set to zero
1 JTWC = 1.4133 x JMAWhen intercept forced to zero
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120 140 160
JMA Vmax 10-min kts
JTW
C V
max
1-m
in k
ts1996: JTWC Vmax VS JMA Vmax
1JTWC = 1.4143 x JMAWhen intercept not forced to zero
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120 140 160
JMA Vmax 10-min kts
JTW
C V
max
1-m
in k
ts
1997: JTWC Vmax VS JMA Vmax
JTWC = (1.5379 x JMA) - 7.7465 1
When intercept forced to zero
1 JTWC = 1.24231 x JMAWhen intercept forced to zero
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120 140 160
1987: JTWC Vmax VS JMA Vmax
JTWC = (1.4544 x JMA) - 17.463 1
When intercept not forced to zero
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120 140 160
JMA Vmax (10-Min)
JTW
C V
max
(1-
Min
)
2002: JTWC Vmax VS JMA Vmax
JTWC = (1.5412 x JMA) - 15.832 1
When intercept not forced to zero
1JTWC = 1.3214 x JMAWhen intercept forced to zero
JTWC = (1.5973 x JMA) - 22.637 1
When intercept not forced to zero
1 JTWC = 1.3028 X JMAWhen intercept forced to zero
JTWC = 0.0067 (JMA)2 + 0.5222 (JMA) + 7.7002
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120 140 160
2004: JTWC Vmax VS JMA Vmax
JTWC = (1.2661 x JMA) - 7.832 1
When intercept not forced to zero
1 JTWC = 1.1676 x JMAWhen intercept forced to zero
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120 140 160
1979: JTWC Vmax VS JMA Vmax
Conclusions:
(1) The differences of wind intensities between the JTWC and the JMA are irreconcilable. There is no uniform or physically meaningful correction that can be applied to the two data sets to bring them into line with each other.
(2) Establish a working group of tropical cyclone diagnostic experts to undertake a project similar to the HRD Hurricane Reanalysis Project for the historical record of the tropical cyclones of thewestern North Pacific.
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