Post on 11-Jul-2018
Global Ensemble Forecasting System performance on Hurricanes Hugo, Georges, and Floyd By
Ana P. Torres And
Richard Grumm National Weather Service at State College, PA NOAA Mission Goal: Weather Ready Nation
Abstract
The performance of the Global Ensemble Forecasting System (GEFS) reforecast data (GEFS-R)
has been put to the test in an endeavor to examine its versatility and accuracy by forecasting three high-
impact tropical cyclones. Doing so provides insight into future uses of the GEFS when forecasting
cyclones. Initial observations indicate a 3-4 day window of predictability can be observed when
predicting several parameters such as mean sea level pressure and precipitable water for the three storms.
In terms of precipitation and the probability of exceeding specific threshold amounts, such as 25, 50 and
100 mm of precipitation, the GEFS-R provided about a 2-3 day window of predictability.
The GEFS-R had biases in the forecast track of each storm and generally underestimated the
intensity of each storm. The CFS’ resolution may have been too coarse to properly analyze the depth of
the hurricanes. The IBTrACS data typically showed deeper cyclones and strong low-level winds about
each cyclone. The limitations of the CFS data relative to the IBTrACS data may have contributed to some
of the errors observed in the GEFS-R forecasts. This may have limited the skill of the GEFS-R over older
forecasts from the operational GFS and GFDL model run in 1999. There was also some indication that
initially weak storms tended to re-curve too early relative to observations, although this tendency
decreased with the strengthening of the storms.
1. Introduction
Weather forecasting is one of the most
inexact sciences because of its dynamic and
ever-changing nature. Scientists have developed
models and systems that help visualize and
predict the future of any given weather
phenomenon with various degrees of certainty.
Ensemble forecasting is a method to obtain
uncertainty information (Sivillo et al. 1997) and
obtain a more probabilistic sense of the forecast
(Toth et al. 2002). Using various forecasts that
can be initialized using perturbed initial
conditions, ensemble forecasts predict a variety
of possibilities for one weather event, providing
a more probabilistic approach to forecasting.
The Global Ensemble Forecasting
System (GEFS) is a global weather forecasting
system that consists of 21 separate members1.
This system was implemented by the National
Centers for Environmental Prediction (NCEP) as
a way to address the uncertain nature of weather
phenomena. It quantitatively measures the
uncertainty of any given forecast by initializing
an ensemble of multiple forecasts that have been
slightly perturbed from the original conditions
(Wei et al 2008; Wei et al 2006). The GEFS is
primarily used to assess synoptic scale weather
phenomena and it is one of the five predominant 1 NCDC, Global Ensemble Forecast System (GEFS), http://www.ncdc.noaa.gov/data-access/model-data/model-datasets/global-ensemble-forecast-system-gefs (July 2013).
synoptic scale medium range ensemble forecast
systems in used worldwide. Thus, understanding
its performance is important to all users of
GEFS data. How the GEFS performs on high
impact-tropical events is paramount to
forecasters in areas affected by tropical storms.
The National Oceanic and Atmospheric
Administration (NOAA) Earth System Research
Laboratory (ESRL) developed a GEFS
reforecast dataset GEFS-R (GEFS: Hamill,
2013) which is comparable to the currently
operational GEFS and runs at about 55km of
horizontal resolution. These data are useful to
examine how the GEFS may have predicted
significant high impact weather events from the
past. Thus, the GEF-R offers an opportunity to
examine how the GEFS may have predicted
major hurricanes such as Hugo, Georges, and
Floyd. The GEFS-R also provides an
opportunity to show which types of displays
may aid in using GEFS data to predict similar
storms in the future.
The ESRL GEFS-R forecasts were initialized
using the Climate Forecast System (CFS: Saha
et al. 2010). The CFS is a fully coupled ocean-
land-atmosphere dynamical seasonal analysis
and prediction system. It was launched by NCEP
in August 2004. It runs on 6-hour intervals and
has a resolution of approx. 38 km. The
reanalysis data sets generated by the CFS
provide dynamically consistent and verifiable
estimates of the climate state in any given area
during the stipulated period of time.
Hurricane Hugo has gone down in
history as one of the costliest and most
destructive hurricanes of the 20th century. Its
path of destruction stretches from the Leeward
Islands to South Carolina during the period of 9-
23 September 1989. Hurricane Georges shares a
similar history; during its 18-day run from 13
September 1998 to 1 October 1998, it exacted a
deadly toll on the Caribbean and Florida.
Hurricane Floyd hit the Bahamas and most of
the East Coast of the United States at the
beginning of the month of September 1999,
leaving in its wake a flood disaster of significant
proportions.
The three aforementioned storms were
all Cape Verde storms. Cape Verde storms tend
to originate as thunderstorm clusters in North
Africa2. As they move into warm waters, they
arrive near the Cape Verde islands, where
conditions can be ripe for cyclonic formation.
Ideal conditions of development include low
shear, low Saharan dust counts, moist air mass,
and water temperatures above 27C. These
systems tend to track west driven by upper-level
steering in the atmosphere and the presence of a
positive North Atlantic Oscillation with a large
subtropical ridge over the Atlantic basin. The
long stretch of warm open water fuels these
systems, giving them time to develop into strong
tropical cyclones. Hurricanes Hugo, Georges
2 Chris Landsea, What is a Cape Verde Storm?, http://www.aoml.noaa.gov/hrd/tcfaq/A2.html (July 2013).
and Floyd all originated within 500 miles of the
Cape Verde islands. They are counted among
the most destructive and fierce tropical cyclones
to affect the Caribbean and the southeastern
United States.
These three hurricanes also exemplify
the effect of the El Niño Southern Oscillation
(ENSO) on cyclonic strengthening. This
phenomenon affects the ocean temperatures in
the Pacific, which in turn affect the atmospheric
conditions in Eastern Asia, Australia, the
Americas and the North Atlantic basin. Warm
episodes tend to lead to the monsoon season in
Asia, while cold episodes cause wetter weather
in the Atlantic basin and the Americas.
According to Bove et al, (1998), the occurrence
of warm episodes – also known as La Niña –
during the period of August-September-October
(ASO) is directly correlated to the increase in
probability of the occurrence of US land-falling
hurricanes. For our three storms, the ENSO
index indicated neutral to cold conditions, which
are conducive to the genesis of strong tropical
cyclones.
This paper provides a historical
overview of 3 high-impact tropical storms.
Forecasts from these storms from the GEFS-R
are presented to demonstrate how ensemble
forecast data may have aided in predicting the
landfall of these systems. The focus here is on
the intensity, location of landfall, and heavy
rainfall information which could have been
extracted from ensemble predictions of these
storms.
2. Synoptic Overview
A. Hugo
Hugo was first detected via satellite
imagery on September 9 as a cluster of
thunderstorms off the coast of Africa. By
September 10, a tropical depression had formed
southeast of the Cape Verde islands, and by 11
September it had intensified into Tropical Storm
Hugo (Case, 1990). Hugo attained hurricane
strength on 13 September about 2000 km east of
the Leeward Islands, and by September 14 it had
wind speeds of 51.4 m/s (100 kts). On
September 15, Hugo attained winds of 139 knots
and a minimum pressure of 918 hPa, making it a
Category 5 hurricane. Striking Guadalupe on
September 17, it started to lose strength and
forward speed; winds decreased to 64.31 m/s
(125 kts), becoming a Category 4 hurricane.
The decreased speed of Hugo only
helped prolong its impact on the Caribbean.
Moving at a 9 MPH, the eye of Hugo passed St.
Croix on the 18th, with winds of 61.73 m/s (120
kts). Just twelve hours later, satellite imagery
placed the eye of Hugo grazing the eastern coast
of Puerto Rico with winds of 53.5 m/s (104 kts).
After crossing Puerto Rico, the storm gained
forward speed but weakened substantially.
(Figure 1)
After affecting the Caribbean, Hugo
entered the open Atlantic, gaining strength and
by 20 September, the hurricane exhibited a more
organized eye and increased forward speeds. As
it reached the Gulf Stream, its forward speed and
wind speed dramatically increased. Hugo
became a Category 4 hurricane for the second
time in its life cycle. On September 22, Hugo
made landfall on the coast of South Carolina
near Charleston with a forward speed of 30
MPH and estimated maximum sustained winds
of 61.21 m/s (119 kts). Hugo then continued
inland as a tropical storm, before dissipating
over the far North Atlantic Ocean on 23
September. (Figure 2)
Rainfall amounts related to Hurricane
Hugo were reported in the range of 100-250mm
(4 to 10 inches) of rain in the Caribbean and the
Carolinas. Official reports from the National
Weather Service Weather Forecasting Office at
San Juan, PR established a rainfall total of 76
mm. In terms of storm surge, the Carolinas
experienced up to 6.1 m (20ft) surges in various
coastal areas. Florence and Sunter, North
Carolina reported tornadoes associated with the
storm as well. Damages caused by Hurricane
Hugo amounted to $9 billion dollars ($17.5
billion as of 2010, due to inflation).
B. Georges
Georges was first identified on 13
September, as a tropical wave exiting the coast
of Africa (Pasch, 2001). By 15 September, the
wave was classified as a tropical depression, and
it became a tropical storm by 16 September.
Georges reached hurricane strength around 1800
UTC on 17 September. It is estimated that
Georges reached a peak intensity of 69.45 m/s
(135 kts) winds at 0600 UTC on 20 September.
After that peak intensity on 20 September,
Georges began to weaken substantially, due to
upper-level vertical shear induced by an upper-
level anticyclone over the eastern Caribbean.
After this weakening, Georges made
landfall in Antigua and St Kitts and Nevis, with
maximum sustained surface winds of 51 m/s
(100 kts). It then made landfall in Puerto Rico
on 21 September, with sustained surface winds
of 51 m/s (100 kts). The interaction with the
orographic elements in the island weakened the
system slightly. After moving into the Mona
Passage on 22 September, Georges re-intensified
and made landfall about 75 miles east of Santo
Domingo with sustained surface winds of 54 m/s
(105 kts). (Figure 3)
Its subsequent passage through
Hispaniola during 22 -23 September continued to
weaken Georges, but it retained hurricane
strength while moving slowly west-
northwestward across the Windward Passage
and the northern coast of Cuba on 24 September.
Once back in open water, Georges began to re-
intensify. On 25 September, Georges made
landfall in Key West, Florida with a minimum
central pressure of 981 hPa and maximum winds
of 46 m/s (90 kts). During the next couple of
days, the system moved slowly towards
Mississippi, making landfall on the morning of
28 with a minimum central pressure of 964 hPa.
Georges was downgraded to tropical storm the
same day. Georges became semi stationary for
the next 12 hours, and then started moving in a
general northeastern direction on the 29
September. It was then downgraded to tropical
depression while located near Mobile, Alabama.
By early 1 October, the system had completely
dissipated near the coast of northeast Florida and
southeast Georgia.
Storm surges were reported in various
locations including Puerto Rico, the Florida
Keys, Louisiana, Mississippi, and Alabama,
with averages in the range of 1.22-3 m (4-10
feet). Fort Morgan, Alabama reported maximum
surge of 3.63 m (11.9 ft). In terms of
precipitation, the US Virgin Islands saw rainfall
totals between 50-200mm (2-8 inches), while in
Puerto Rico, the rainfall range fell between 250-
350mm (10 to 14 inches). Meanwhile, in the
Keys the maximum reported total was
212.85mm (8.34 inches). Georges also produced
twenty-eight tornadoes in the southeastern
region of United States.
Hurricane Georges exacted a high death
toll, with 602 reported deaths, most of them in
Hispaniola. Table 2 summarizes the storm-
related casualties. Total damages in the
Caribbean and the US reached the $6 billion
mark, with $3 billion of those happening in the
continental US and its territories.
C. Floyd
Floyd was first identified as a tropical
wave emerging from West Africa on 2
September. The system was disorganized and
showed little promise of convective
development. However, by 7 September the
wave had developed enough of a curved band of
deep convection and a consolidated cloud
pattern to be classified as a tropical depression.
It was later classified as Tropical Storm Floyd
on 8 September, about 750 miles east of the
Leeward Islands (Lawrence, 2001).
Floyd became a hurricane by 1200 UTC
10 September. It strengthened to category 3
during the next couple of days; however, it
interacted with the southwest portion of the mid-
Atlantic upper-troposphere trough, which
disrupted its upper level flow and caused it to
weaken on the 12th. After this weakening
episode, Floyd experienced a sustained
strengthening period, caused in part by its
westward motion and the presence of enhanced
upper ocean heat content in the area. By 1800
UTC 13 September, Floyd was a Category 4
tropical cyclone, with maximum sustained winds
of 70 m/s (135 kts).
Late on the 13th, Floyd blew over the
Bahamas, making landfall on Eleuthera by 14
September, later going on to strike Abaco in the
afternoon. It continued to move parallel to
Florida, headed straight to the Carolinas. Floyd
made landfall near Cape Fear, North Carolina by
600 UTC 16 September as a category 2
hurricane with estimated maximum winds near
46 m/s (90 kts). After making landfall, it
weakened substantially to become a tropical
storm, and then continued moving swiftly along
the coast of Delaware and New Jersey. It
reached Long Island by 0000 UTC 17
September. At this moment, Floyd became
involved with a frontal low over the Eastern
seaboard, and thus became an extratropical
system by 1200 UTC 17 September. By the 19
September, it was no longer a distinguishable
entity. (Figure 4)
Rainfall totals as high as 350 mm to
500mm (12 -14 inches) were reported in North
Carolina, Virginia, Maryland, Delaware and
New Jersey. In Philadelphia, a record was set for
most rain in a calendar day: 168.4 mm (6.61
inches). Storm surge of 2.5-3 m (9 to 10 ft)
experienced in the North Carolina coast. At least
15 tornadoes were reported in eastern North
Carolina and the Wilmington area. One of the
confirmed tornadoes destroyed two houses and
damaged four others.
Damages associated with Floyd ranged
between 3 and 6 billion dollars. Floyd caused 57
fatalities, 56 of which were in the United States
including 6 fatalities in Pennsylvania. Floyd was
the deadliest hurricane in the US since Agnes in
1972.
3. Methods
The tropical cyclones studied in this
project were selected based upon the following
criteria: they had to have occurred prior to the
implementation of the GEFS; they must have
reached Category 3 intensity as ranked by the
Saffir-Simpson scale; and they must have had a
significant impact on the Caribbean and
continental United States. Thus, Hurricane Hugo
(1989), Georges (1998), Floyd (1999), and Fran
(1996) were chosen.
Various datasets were obtained,
including the CFS reanalysis for the dates
chosen, the GEFS-R forecasts for the same
periods of time, total rainfall amounts as
measured by the Tropical Rainfall Measuring
Mission (TRMM) and the best cyclone tracks
from the International Best Track Archive for
Climate Stewardship (IBTrACS). Not all
datasets spanned the years of the studied storms.
For example, Hugo occurred before the
evolution of TRMM data. All of the data were
plotted and analyzed using the Grid Analysis
and Display System (GrADS) desktop tool. Post
analysis data and some plots were made using
Excel.
The CFS reanalysis data was used to
obtain a close approximation of the actual
atmospheric conditions at the times of the
storms, and provided a control to visualize each
storm. Some of the parameters plotted and
analyzed from the dataset were mean sea level
pressure (MSLP), 850mb heights, and the
precipitable water (PW). These data were plotted
along with departures from normal of these data
in standard deviations from normal as described
by Hart and Grumm (2001).
The GEFS-R forecast data was plotted
and analyzed for the same parameters.
Additionally, track and intensity data were
obtained from the two datasets using GrADS to
obtained the lowest pressure and estimate the
winds near the point with the lower MSLP. The
grid point data obtained using this method were
put into Excel to compare to other datasets and
to produce the track forecasts.
The GEFS-R forecast of quantitative
precipitation (QPF) were also analyzed and
plotted in GrADS. The probabilities of the QPF
exceeding various thresholds were computed
along with the GEFS-R mean QPF. These data
were compared to available verification data to
qualitatively assess the ability of the GEFS-R to
predicted areas of heavy rainfall associated with
each system. The best storm track data from
IBTrACS provided verified and reliable storm
track and intensity data that could be used on a
control basis for comparison against the GEFS-
R and the CFS. The data included coordinates,
mean sea level pressures, maximum sustained
winds, and storm intensity as described by the
Saffir Simpson scale. This was compared with
the track and intensity data from the CFS and the
GEFS-R.
The same process was used when
studying data for Hurricane Floyd from three
operational models: the UKMET, the AVN (now
GFS), and the GFDL. Track and intensity data
was obtained from the model, and compared to
verify for accuracy. In order to better understand
the statistical nature of the data studied,
Microsoft Excel was used to run statistical
analysis of the average errors.
4. Results and Discussion
i. Track and Intensity Forecasts
When comparing the CFS tracks for
Hugo to the IBTrACS best track data (Figure 5),
it’s evident that the CFS has considerable skill in
matching the path of the storm. A similar
behavior could be observed when the CFS tracks
for Georges (Figure 6) and Floyd (Figure 7)
were compared to the IBTrACS data.
For Hurricane Hugo, the average error
for the location of the storm at any given time
was about 20 km. In Georges’ case, the average
error for latitude and longitudes was about 30
km in any direction. Finally, for Hurricane Floyd
the average error was also approximately 30 km.
All values fall within the 95% confidence
interval. This validates the CFS’ ability to
correctly approximate the position of the storm
at any given time.
Point data for mean sea level pressure
from the CFS reanalysis and the IBTrACS were
compared for all storms. The differences
between the reanalysis values and the measured
values were considerable. These data showed
that the CFS had a limited ability to capture the
intensity of tropical storms. The pressure
differences for Hurricane Hugo were the most
noticeable. At its most intense moment, the CFS
was estimating a storm with pressures 66 hPa
greater than the measured values (Table 1). In
general, the CFS consistently underestimated
Hugo’s depth. The same behavior was observed
for Georges; the storm was estimated to be
between 30 to 70 hPa weaker than it actually
was (Table 2). Floyd was no exception; the
storm was also estimated to be up to 50 hPa
weaker than measured (Table 3). The CFS was
unable to obtain the intensity of tropical
cyclones relative to the IBTrACS data.
Maximum sustained winds point data
were also compared for Hurricane Hugo (Table
4). The data reflected significant departures in
the CFS estimates from the IBTrACS expected
values (at its strongest point, the CFS estimated
winds 40 knots below the observed values; at its
weakest, it was overestimating by 30 knots).
After establishing the quality and
limitations of the CFS reanalysis data, the
GEFS-R forecasts were examined. When
looking at Hurricane Hugo’s forecasts for
landfall in Puerto Rico (by 0000 UTC 18
September 1989), a 2-3 day window of
predictability was evident (Figure 8).
As expected, these forecasts show that
longer range predictions had larger errors. For
example, the GEFS-R initialized at 19
September 0000 UTC (Figure 8.f) had a weaker
cyclone northeast of Puerto Rico while shorter
range forecasts (Figure 8.a) showed a
significantly deeper storm. The ensemble mean
and spread diagrams (not shown) indicated
higher uncertainty in the longer range forecasts.
This uncertainty information could be obtained
by visually inspecting the track forecasts
(Figure 9) which show larger spread in the
tracks from earlier over the Eastern Caribbean
and the Leeward islands versus tracks from later
forecasts further west. The storm tracks garnered
for the 6-day period showed that during the early
stages of formation, when the storm was still
weak, the GEFS-R re-curved the storm too early.
This tendency was less apparent as the storm
strengthened and the GEFS was likely better
able to initialize the storm. Thus, the GEFS-R
was able to forecast landfall locations and time
with better accuracy at shorter forecast lengths
and when a deeper cyclone was in the GEFS-R
initialization.
This early re-curving tendency was also
identified by National Hurricane Center (NHC)
operational models back in 1989, especially by
the CLIPER and NHC83 models; the two
models consistently re-curved the storm much
too fast. Given the nature of these two
operational models (CLIPER is a statistical
model, while NHC83 is statistical and
dynamical); the re-curving was attributed to the
climatology of the area (Ward, 1990).
The GEFS-R forecasts for Hurricane
Georges presented a 3-4 day window of fair
predictability when examined for mean sea level
pressures (Figure 10) and precipitable water
(Figure 11). The ensemble tracks, when
compared with the verified CFS track also
exhibited the early re-curving tendency observed
with Hurricane Hugo (Figure 12). As with
Hugo, this tendency was very evident while the
storm is still weak. Unlike Hugo, the GEFS-R
did re-curve the storm when it was weakening,
taking it too far inland.
The GEFS-R was better at forecasting
Hurricane Floyd. When looking at the ensemble
spread for Floyd, the re-curving tendency
evidenced with the other storms is present, but it
is not as dominant (Figure 13). The GEFS-R
actually presented a small cone of variability for
storm landfall.
The CFS Reanalysis track was
consistent with the 72 hr forecasts made by the
UKMET, AVN and GFDL (Figure 14). Early
runs of the GEFS-R while Floyd is still
strengthening cannot match the tracks or storm
depths forecasted by the three operational
models. Nevertheless, the model forecasts and
GEFS-R 1-2 days before landfall show more
predictability. The three models suffer from the
same limitations as the CFS in that they are
unable to specify the true depth of the hurricane;
only the GFDL comes close. Despite deep
cyclone forecasts, the GFDL suffered from a
tendency to curve storms too slowly and traced
them far too inland.
ii. Precipitation Forecasts for Hugo
According to reports gathered and
published by the National Hurricane Center, San
Juan, Puerto Rico received a two-day total
rainfall accumulation of 76 mm after the impact
of Hurricane Hugo on 18 September 1989. No
TRMM data was available for this period of
time. After running the GEFS-R, the probability
of quantitative precipitation amounts exceeding
the 70mm threshold was 60% for a two-day
forecast window; the one day window exhibited
probabilities of 90% (Figure 15). Furthermore,
the average QPF and 150mm contours show
probabilities of at least exceeding 50mm of
precipitation within a five day window. In
general, this provides a 3-4 day window of
predictability for the GEFS-R (Figure 16).
iii. precipitation forecasts Georges
The TRMM data accessed for Hurricane
Georges reveals estimates upwards of 100mm of
total rainfall after Georges made landfall in
Puerto Rico on 21 September 1998 (Figure 17).
The probability of quantitative precipitation
amounts exceeding that amount, as provided by
the GEFS-R, were 90% one day out; after four
days, the forecast was still predicting a 50%
probability of rainfall exceeding 100mm. This
provides an impressive 5-day window of
predictability for the GEFS-R QPF product.
5. Summary
Hurricanes Hugo, Georges and Floyd
were examined in terms of their storm tracks,
intensity and total precipitation probabilities
using IBTrACS, CFS, and the GEFS-R as
plotted and analyzed by GrADS.
The IBTrACS best storm track data set
delivered high resolution information and insight
into each storm’s intensity. It helped highlight
the short-coming of the CFS in that particular
aspect. Clearly, the CFS had difficulty analyzing
the true depth of tropical cyclones. The CFS did
relatively well in providing useful tropical
cyclone track information.
The CFS provided a good first guess as
to the general synoptic pattern of each storm. It
also provided a confident guess of the storm
tracks. The intensity issue was likely a serious
CFS limitation when using it to GEFS-R likely
was at a disadvantage in predicting the evolution
of hurricanes Hugo, Georges, and Floyd. It is
unclear how well the method used to produce
perturbations for the GEFS-R handles tropical
storms. But the sensitivity of forecasts to initial
conditions was a significant issue with the
GEFS-R forecasts of these 3 hurricanes.
The results here suggest that while the
CFS reanalysis can be relied upon for tracking
tropical cyclones, its estimates for mean sea
level pressure are very unreliable. And this mean
sea-level pressure and thus weaker vortex issue
likely are a significant constraint when making
retro-forecasts with single models or and an
ensemble forecast system.
The GEFS-R shown here likely
suffered from the limitations brought on by the
CFS initial conditions. There was a general
tendency in the forecasts to re-curve weak
storms too soon; this tendency diminished as the
storms strengthened in the CFS. Nevertheless,
the forecasts shown here exhibited a reasonable
2-3 day window of predictability in terms of
landfall locations and times, and 3-5 day
windows of high predictability when predicting
significant tropical rainfall totals.
The forecasts made by the GEFS-R for
Hurricane Floyd were found to be comparable to
operational model runs. Of these operational
models, only the GFDL was better able to
predict the intensity of the cyclone. The
limitations exhibited by these models might be
attributable to the bogusing techniques used at
the time to initialize tropical storms (Serrano,
1994). It would be interesting to see of a
cyclone bogusing technique could be used to
improve forecasts of the GEFS-R when using
the CFS as a background states.
6. Acknowledgements
I’d like to acknowledge my mentor
Richard Grumm, who was instrumental in the
making of this project, Bob Hart for his
guidance and contributions to the project, and
everybody in the WFO in State College, whose
support and day to day help were invaluable to
me.
Finally, I’d like to thank the Educational
Partnership Program staff for this opportunity
and for their guidance throughout the process.
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8. Figures
Figure 1– CFSR 00 UTC 15 September 1989 – 00 UTC 20 September 1989 mean sea level pressure anomalies.
Figure 2 - CFSR 18 UTC 19 September 1989 – 06 UTC 22 September 1989 mean sea level pressure anomalies.
Figure 3 - CFSR 00 UTC 19 September 1998 – 00 UTC 24 September 1998 mean sea level pressure anomalies.
Figure 4 - CFSR 12 UTC 14 September 1999 – 00 UTC 17 September 1999 mean sea level pressure anomalies.
Figure 5 - Hurricane Hugo (1989) CFS Reanalysis storm track superimposed over IBTrACS best storm track.
Figure 6 - Hurricane Georges (1998) CFS Reanalysis storm track superimposed over IBTrACS best storm track.
Figure 7 - Hurricane Floyd (1999) CFS Reanalysis storm track superimposed over IBTrACS best storm track.
Table 1 - Comparison of mean sea level pressures from CFS and IBTrACS for Hurricane Hugo.
Table 2 - Comparison of mean sea level pressures from CFS and IBTrACS for Hurricane Georges.
DTG IBTrACS CFS Difference00Z15SEP1989 962 1007 4506Z15SEP1989 957 1005 4812Z15SEP1989 940 1006 6618Z15SEP1989 918 1005 8700Z16SEP1989 923 1003 8006Z16SEP1989 927 1003 7612Z16SEP1989 940 1004 6418Z16SEP1989 941 1002 6100Z17SEP1989 941 1003 6206Z17SEP1989 943 1003 6012Z17SEP1989 949 1001 5218Z17SEP1989 945 1000 5500Z18SEP1989 934 998 6406Z18SEP1989 940 994 5412Z18SEP1989 945 995 5018Z18SEP1989 958 993 3500Z19SEP1989 959 992 3306Z19SEP1989 962 992 3012Z19SEP1989 964 992 2818Z19SEP1989 966 994 2800Z20SEP1989 957 991 3406Z20SEP1989 957 991 3412Z20SEP1989 958 989 3118Z20SEP1989 953 989 3600Z21SEP1989 950 988 3806Z21SEP1989 950 986 3612Z21SEP1989 948 986 3818Z21SEP1989 944 984 4000Z22SEP1989 935 981 4606Z22SEP1989 952 986 3412Z22SEP1989 975 990 1518Z22SEP1989 987 994 700Z23SEP1989 988 991 3
Mean Sea Level PressureDTG IBTrACS CFS Difference00Z18SEP1998 984 1006 2206Z18SEP1998 977 1008 3112Z18SEP1998 973 1006 3318Z18SEP1998 970 1006 3600Z19SEP1998 970 1005 3506Z19SEP1998 965 1006 4112Z19SEP1998 954 1005 5118Z19SEP1998 949 1006 5700Z20SEP1998 939 1002 6306Z20SEP1998 937 1003 6612Z20SEP1998 939 1001 6218Z20SEP1998 956 1002 4600Z21SEP1998 963 1001 3806Z21SEP1998 966 1001 3512Z21SEP1998 966 1002 3618Z21SEP1998 970 999 2900Z22SEP1998 970 1002 3206Z22SEP1998 972 1001 2912Z22SEP1998 964 999 3518Z22SEP1998 970 998 2800Z23SEP1998 980 998 1806Z23SEP1998 990 998 812Z23SEP1998 996 999 318Z23SEP1998 994 999 500Z24SEP1998 992 999 706Z24SEP1998 991 998 712Z24SEP1998 990 998 818Z24SEP1998 989 999 1000Z25SEP1998 987 1000 1306Z25SEP1998 986 999 1312Z25SEP1998 982 1000 1818Z25SEP1998 975 998 23
Mean Sea Level Pressure
Table 3 - Comparison of mean sea level pressures from CFS and IBTrACS for Hurricane Floyd.
Table 4 - Comparison of maximum sustained winds from CFS and IBTrACS for Hurricane Hugo.
DTG IBTrACS CFS Difference18Z07SEP1999 1008 1009 100Z08SEP1999 1007 1010 306Z08SEP1999 1005 1008 312Z08SEP1999 1003 1008 518Z08SEP1999 1000 1007 700Z09SEP1999 1000 1007 706Z09SEP1999 1003 1005 212Z09SEP1999 1003 1005 218Z09SEP1999 996 1004 800Z10SEP1999 995 1004 906Z10SEP1999 990 1002 1212Z10SEP1999 989 1003 1418Z10SEP1999 975 1000 2500Z11SEP1999 971 999 2806Z11SEP1999 963 996 3312Z11SEP1999 962 995 3318Z11SEP1999 966 992 2600Z12SEP1999 967 991 2406Z12SEP1999 960 991 3112Z12SEP1999 955 991 3618Z12SEP1999 940 987 4700Z13SEP1999 931 987 5606Z13SEP1999 922 984 6212Z13SEP1999 921 984 6318Z13SEP1999 923 980 5700Z14SEP1999 924 977 5306Z14SEP1999 927 976 4912Z14SEP1999 930 973 4318Z14SEP1999 930 972 4200Z15SEP1999 933 973 4006Z15SEP1999 935 973 3812Z15SEP1999 943 975 3218Z15SEP1999 947 977 3000Z16SEP1999 950 978 2806Z16SEP1999 956 979 2312Z16SEP1999 967 983 1618Z16SEP1999 974 984 1000Z17SEP1999 980 986 606Z17SEP1999 983 988 512Z17SEP1999 984 988 418Z17SEP1999 985 989 400Z18SEP1999 987 992 506Z18SEP1999 990 993 312Z18SEP1999 992 992 018Z18SEP1999 992 992 0
Mean Sea Level Pressure Maximum Sustained WindsIBTrACS CFS Difference
9/15/1989 0:00 100 42 -589/15/1989 6:00 110 59 -51
9/15/1989 12:00 125 66 -599/15/1989 18:00 140 49 -91
9/16/1989 0:00 135 83 -529/16/1989 6:00 130 62 -68
9/16/1989 12:00 120 84 -369/16/1989 18:00 120 85 -35
9/17/1989 0:00 120 73 -479/17/1989 6:00 120 69 -51
9/17/1989 12:00 125 71 -549/17/1989 18:00 125 68 -57
9/18/1989 0:00 130 90 -409/18/1989 6:00 120 100 -20
9/18/1989 12:00 110 83 -279/18/1989 18:00 105 90 -15
9/19/1989 0:00 100 98 -29/19/1989 6:00 90 92 2
9/19/1989 12:00 90 91 19/19/1989 18:00 90 97 7
9/20/1989 0:00 90 87 -39/20/1989 6:00 90 85 -5
9/20/1989 12:00 95 118 239/20/1989 18:00 95 109 14
9/21/1989 0:00 100 117 179/21/1989 6:00 100 112 12
9/21/1989 12:00 110 111 19/21/1989 18:00 120 115 -5
9/22/1989 0:00 120 109 -119/22/1989 6:00 85 107 22
9/22/1989 12:00 55 89 349/22/1989 18:00 40 62 22
9/23/1989 0:00 35 67 32
Figure 9 - Hurricane Hugo CFSR storm track superimposed over GEFS-R ensemble member forecasts from 11 September 1989 to 17 September 1989.
Figure 10 - GEFS-R mean sea level pressure and departures for Hurricane Georges, valid 00Z22SEP1998.
Figure 12 - Hurricane Georges CFSR storm track superimposed over GEFS-R ensemble member forecasts from 16 September 1998 to 30 September 1998.
Figure 13 - Hurricane Floyd CFSR storm track superimposed over GEFS-R ensemble member forecasts from 7 September 1999 to 19 September 1999.
Figure 14 - Hurricane Floyd CFSR storm track superimposed over GEFS-R ensemble member forecasts and real time forecasts made by the AVN, UKMET and GFDL from 7 September 1999 to 19 September 1999.