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Midlatitude Trough Interaction with the Extratropical Transition of
Hurricane Michael
Stephen R. Guimond
Center for Ocean-Atmospheric Prediction Studies, The Florida State University, Tallahassee, Florida
11 April 2005
ABSTRACT
The interaction of Hurricane Michael (2000) with a Midlatitude Upper Tropospheric Trough
(MUTT) as the storm was undergoing Extratropical Transition (ET) is examined. The utility of a potential
vorticity (PV) framework for diagnosing the dynamic response of a Tropical Cyclone (TC) to an influx of
high PV air in a baroclinic environment will be assessed.
Output from the Aviation model (AVN) with a grid resolution of 1 was manipulated to calculate the
full PV on horizontal isentropic surfaces and vertical cross sections to capture both the MUTT interaction
and ET process. In addition, rain rates from the Special Sensor Microwave/Imager (SSM/I) were analyzed
to provide a quantitative evaluation of the structural changes observed during an ET event that could assist
the operational community.
Results indicate that a trough interaction can be inferred from SSM/I data as the mean area average rain
rate centered on the storm increased with distance from the TC center, a typical signature of the asymmetric
structural change observed during trough interaction cases. PV was shown to be a rather versatile
parameter with the ability to provide a dynamically sound depiction of the kinematics involved with a
MUTT interaction and ET event that will continue to improve upon research into the complex prediction of
TC intensity change.
1. Introduction
The impacts of Midlatitude Upper Tropospheric Troughs (MUTTs) on Tropical
Cyclones (TCs) are numerous. From a movement perspective, MUTTs can rapidly
accelerate the translational speed of TCs as well as the direction of storm motion with the
majority recurving to the north or northeast in the northern hemisphere (Jones et. al 2003;
WMO 1995). From a structural standpoint, prolonged interaction with a MUTT can
transform a TC from a warm-core symmetric vortex in a barotropic environment into a
cold-core asymmetric vortex within a baroclinic environment, a process referred to as
Extratropical Transition (ET) (Jones et. al 2003). The movement of a TC into an
environment associated with a large temperature gradient allows for complex interactions
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to take place between the transitioning storm and intense synoptic scale frontal systems.
A key component of these interactions are the frontogenetic/frontolytic processes that
occur as the front approaches and merges with the TC, a topic the author will address for
his Master’s Thesis. The greatest challenges to operational forecasters during an ET
event are the potentially massive amounts of precipitation, continuation of high winds
with an expansion of the overall wind field and the development of large ocean swells
(Abraham et. al 2004; Jones et. al 2003). The structural changes that occur with ET can
have dramatic impacts for the Canadian Maritimes and marine communities as well as
coastal locations in Western Europe (Abraham et. al 2004). Providing accurate and
timely warnings for these impacts can be difficult especially when so little is known
about the complete ET process. Finally, from an intensity/strength point of view, MUTT
interactions with TCs can cause significant pressure drops on the order of several tens of
millibars due to a secondary circulation feedback that results in a firing of eyewall
convection and amplified low-level wind speeds (Hart 2005, personal communication).
In this study, the MUTT interaction as well as the ET of Hurricane Michael (17-19
October 2000) will be examined and shown to undergo a similar motion, structure and
intensity change to that of the generalization of such storms mentioned above (Stewart
2000). In order to describe the MUTT and ET evolution of Hurricane Michael, both
synoptic and dynamic perspectives will be considered that follow the general flow of
recent research on these subjects.
a. Distinguishing MUTT interaction from ET
It is important for the operational and research communities to bin storms into certain
categories in order to discern a typical pattern of evolution that will assist in improving
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the track, intensity and structural changes lacking in current forecasts. The main
difference between a trough interaction and the extratropical transitioning process of a
TC is the role of the trough in the structural change process. In trough interactions, a
MUTT usually involves a rather short merging period with the TC on the order of 12-24
hours with the interaction usually resembling a smaller scale PV anomaly from the
MUTT intensifying the TC (Molinari et. al 1998; Hanley et. al 2001).
However, during
the majority of ET events, the MUTT drives the evolution of the storm and therefore
produces longer merging time periods lasting several days with the interaction depicting a
deeper, wider PV anomaly from the MUTT advecting over and wrapping around the TC
(Hart 2005, personal communication; Jones et. al 2003).
b. Framework of paper
A large portion of the dynamic component of this study will focus on the use of
potential vorticity (PV) reasoning to explain how the approach of a MUTT can enhance
the secondary circulation of a TC. This secondary circulation is necessary to maintain
the primary circulation from the dissipative effects of angular momentum loss to the sea
surface (friction) and thermal energy loss due to radiative (evaporation) and adiabatic
(ascent) cooling (WMO 1995). It has been argued by Molinari et. al 1998, among
others, that PV provides for a more concise, beneficial dynamical skeleton of TC-trough
interactions than simply using basic variables such as vorticity, height and wind. Strong
motions through a heat source (latent heat releasing convective clouds) follow lines of
constant angular momentum and motions through a momentum source (MUTT or upperlevel jet) follow lines of constant potential temperature (WMO 1995). Thus, because of
the quasi-conservative properties of PV along surfaces of constant potential or equivalent
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temperature, one can follow the motion of air parcels along isentropic surface at higher
levels in the atmosphere where the trough and TC interact. In addition, PV links the
dynamic and thermodynamic properties of the atmosphere together into one formulation
while the traditional vorticity equation relies on implied heating from the divergence and
twisting terms allowing for a more direct interpretation of the physical processes
occurring in TC-trough interactions (Molinari et. al 1998).
2. Physical Mechanisms of PV Intensification
PV anomalies (relative to the surrounding environmental PV) can have enhancing or
diminishing effects on the intensity of a TC that can become complex to diagnose. An
important question to consider is how the strength and duration of negative influences
from a MUTT will augment and overtake the positive influences especially at close
distances to a TC. A fine line exists between a “good” trough and a “bad” trough because
in many instances a catch exists that may render the initial intensity change useless or
reverse the process. The following sub-sections will explain these processes in detail.
a. Positive Influences
When an approaching synoptic scale trough moves within a certain distance (see
Hanley et. al 2001) of a TC, the PV anomaly associated with the trough begins to become
somewhat spatially and temporally coincident with the TC center, a procedure referred to
as the “superposition principle”. When this happens, intensification of the TC can occur
out of a combination of two main processes. First, “constructive interference” occurs
where large eddy PV fluxes moving inward from the trough to the TC allow for enhanced
cyclonic spin-up of the initial vortex and the excitation of a conditional instability of the
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second kind (CISK) type response. Second, enhanced upward motion and an associated
evaporative-wind feedback (“WISHE”) results from several different processes that may
combine to produce the intensification. These include: (i) increasing cyclonic vorticity
advection with height associated with the approaching trough in a Q-G omega
framework, (ii) location of the TC core within the left front or right rear jet streak
quadrants and (iii) enhanced evacuation of air near the tropopause due to a jet streak
increasing the outflow anti-cyclone aloft (Hart 2005, personal communication). When (i)
is coupled with low static stability well outside the core of the TC, a surface induced
circulation can form seen through relatively lower values of vorticity. If this rotation is
within a certain distance from the TC center, the long “arms” of the TC’s vorticity will
tend to draw in sources of angular momentum and thus produce an enhancement of the
cyclonic rotation (Hart 2005, personal communication).
b. Negative Influences
The effects of vertical wind shear on a TC are well known (WMO 1995; Molinari et.
al 1995; Molinari et. al 1998; Hanley et. al 2001). The general consensus on the effects
of vertical wind shear are to displace the heating and convection away from the center of
the storm, which does not allow for an area of focused heating to produce the pressure
falls necessary to maintain and/or strengthen a TC (Hart 2005, personal communication).
The displacement of the heating aloft acts to ventilate the upper troposphere warm
anomaly while decoupling the lower atmospheric frictional convergence and latent heat
release. This process can be seen from satellite imagery when the low-level rotational
center is displaced from the cirrus canopy and the TC begins to take on a more
asymmetric appearance (Beven seminar, 2005). Dry air intrusions act to destabilize the
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sounding away from the TC core producing unfocused convective heating ultimately
resulting in a decrease of warm-core maintenance and the typical destruction of a TC.
c. The Catch
Generally speaking, larger troughs enable greater constructive interference effects of
upper PV anomalies from the trough and lower PV anomalies from the TC that can lead
to intensification. However, larger troughs produce substantial, long-lasting values of
vertical wind shear that will destroy convection surrounding the TC and thus, the catch.
A key aspect of the intensification from positive influences is a thinning of the
approaching positive PV anomaly that attempts to match the scale of the TC’s positive
PV anomaly. Deep convection surrounding the TC core along with the placement of an
upper-level jet to the north of the storm, which will increase the evacuation of air at high
levels, will act to lift the tropopause and build the ridge downstream. The result of this
process will enhance the outflow anticyclone and thus decrease the horizontal scale of the
trough producing the necessary thinning (Hart 2005, personal communication). The
above process allows smaller-scale PV anomalies that can have substantial magnitudes to
approach the TC core without experiencing the detrimental effects of vertical wind shear.
3. Data and analysis method
a. Data
Twelve-hourly 1 gridded analyses are taken from the Aviation model (AVN) from 00
UTC 15 October 2000 through 00 UTC 22 October 2000 which spans the period that
Michael was a hurricane (17-19 October 2000) (Stewart 2000). In addition, the National
Hurricane Center’s (NHC) “best track” dataset from 20 November 2000 was used for the
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precise timing, positioning and intensity (based on central pressure and wind speed) of
Hurricane Michael as the storm traversed the Atlantic Ocean (Stewart 2000). Rain rates
from the Special Sensor Microwave Imager (SSM/I) on 0.25 resolution swaths taken
from Remote Sensing Systems were used to diagnose the structural changes in
precipitating convection of Michael (www.remss.com). Three different satellites (F13,
F14, F15) were used to provide the densest network of precipitation measurements
around the time of trough interaction with the storm.
b. Diagnostics
To make use of the SSM/I data, the time each satellite passed over the TC was found
and linear interpolation between successive “best track” positions was used to find the
approximate center of the TC at the time of satellite overpass. This process produces a
TC center that is within a few tenths of a degree of the actual center due to the resolution
of the satellite. Typical TC eye diameters range from ~15-30 km and are thus on scales
smaller than the resolution of the satellites (WMO 1995). As a result, the rain rates
retrieved from the satellites at the TC “center” are most likely picking up on the intense
precipitation occurring just outside of the eye within the eyewall and beyond. To
facilitate an analysis of how the structure of precipitating convection changes upon
MUTT interaction and during the early stages of ET, 1x1, 2x2 and 3x3 area
averages positioned about the TC center were calculated and reported in Table 1.
Many of the dynamical techniques used by previous authors to explain both MUTT
and ET processes will be incorporated in this study including vertical wind shear and the
full PV.
7
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The vertical wind shear was calculated as a simple vector difference between the 850
and 200 mb layers given by
VS  V200  V850 ,
(1)
where V200 is the vector wind at 200 mb, V850 is the vector wind at 850 mb and VS is the

shear vector within the layer.

In order to plot vertical crosssections of PV in pressure coordinateform, the full PV
equation can be expressed as

V


PV  g p  f   kˆ     p ,
p
p


(2)
where  p is the vertical component of relative vorticity in pressure coordinates,  p is the

horizontal gradient operator evaluated on a pressure surface and V is the horizontal wind


(Hanley et. al 2001). The full PV, which incorporates the twisting of horizontal potential

temperature gradients seen in the second term of (2), will be expressed in the almost
universal potential vorticity units [PVU, where 1 PVU = 1106 m 2Ks1kg1 ; Hoskins et
al. (1985)]. Plots of PV in the horizontal plane on a representative isentropic surface,
which allows one to view the interaction of the 
MUTT and TC as air flows along constant
potential temperature, will be shown at the same times as the vertical cross sections to
enable a thorough kinematic description of the trough interaction and ET process. To
produce isentropic surfaces, a desired potential temperature value is interpolated between
pressure levels to produce a field of coefficients, which is then used as a weighting
function to find the appropriate value of PV (calculations done in FERRET). This
process pulls out high PV air from both the MUTT and TC to view their interaction at
various levels in the atmosphere.
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4. Results
a. Remote Sensing Component
Table 1 contains the rain rates area averaged about the TC center of Hurricane Michael
from the 18 October 2000 through the 19 October 2000. As mentioned previously, the
rain rates at the TC’s “center” are shown along with 1x1, 2x2 and 3x3 box averages
to show the structural changes occurring during a MUTT interaction and ET process. On
the 18th of October, the rain rates at the center of Michael are on average quite large (~13
mm/hr) with fluctuations (max = 21.20 mm/hr, min = 3.00 mm/hr) in the intensity due to
approximating the TC center and normal structural variability in the eyewall. On the
19th of October, rain rates are shown to increase to rather impressive levels (max = 25.00
mm/hr) early on in the day. SSM/I has an upper threshold level in rain rate returns of
25.00 mm/hr, therefore it is likely that Michael was producing more intense rainfall as
this time than the satellite can detect. The 18th and 19th of October were chosen to
exemplify the shift from a symmetric TC to a more asymmetric structure upon interaction
with a MUTT. At 1324 and 1400 UTC October 19th the rain rates changed dramatically
near the TC center to much lower intensities than previously observed. In addition, every
other time period besides the two above displayed a decrease in the rain rate averaged
over each box about the TC center, going from highest in the 1x1 box to lowest in the
3x3 box. At 1324 UTC on the 19th, the rain rate went up from 2.04 mm/hr in the 1x1
box to 4.87 mm/hr in the 3x3 box. Similar results were found at 1400 UTC on the 19th
with a rain rate of 2.36 mm/hr in the 1x1 box to 4.79 mm/hr in the 3x3 box. As a
supplement to these data, the NHC’s best track reports a 14 mb pressure drop in the six
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hour period between 1200 UTC on the 19th to 1800 UTC on the 19th, a pressure change of
more than 2.25 mb/hour (Stewart 2000). The structural and intensity changes observed
during this time period are attributed to the interaction of a MUTT with Michael as can
be seen in the Geostationary Operational Environmental Satellite (GOES) 8 water
vapory imagery at 1200 UTC 19th October in Figure 1. The MUTT displaced the core of
intense precipitation away from Michael’s center and as the TC began to rotate, the
majority of heavy rainfall was located off to the north and northwest of the eye. This
analysis indicates that structural changes in box averaged rain rates about the TC center
can be a useful tool for diagnosing a trough interaction and the early stages of ET, which
can be extended to include the complete ET process if so desired.
b. Synoptic and Dynamic Component
A step-by-step analysis of each twelve hour period from the GFS beginning 0000
UTC 19th October 2000 and ending 1200 UTC 20th October 2000 will be examined with
heavy weight on PV-thinking to describe both the MUTT interaction and ET of
Hurricane Michael.
Figure 2a displays the horizontal plot of PV on the 335 K isentropic surface for 0000
UTC on the 19th overlaid with horizontal wind vectors and the hurricane symbol
indicating the model’s location of the TC center at this time. From the plot, the center of
Michael can be seen by the patch of ~1 PVU air out in the Atlantic Ocean with the
strongest gradient of PV at 1.5 PVU (nominal tropopause level) and greater at ~434 km
from the TC center representing the trough. The distance inferred from Figure 2a is on
the lower end of the favorable distant interaction composite (PV maxima between 400
and 1000 km from TC center) as described by Hanley et al. 2001. The corresponding
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time of vertical cross section (sliced at 34N) in Figure 2b shows the maximum PV
anomaly associated with the TC concentrated in the lower portions of the atmosphere
between 800 and 900 mb. Contours of potential temperature clearly show the warm core
structure of the TC at this time with the tropopause (thick black line) at a fairly high,
constant height. Figure 2c shows the vertical wind shear in the 200 – 850 mb layer to be
quite low in the vicinity of the TC but with higher values associated with the trough to
the northwest and jet maximum to the north. The relative humidity at 700 mb is between
80-90 % in the region of the TC which will help to sustain the convective core, but drops
off rather quickly near the trough location depicted in Figure 2d.
At 1200 UTC 19th October, the MLUTT has moved within ~325 km of the TC center
and is now defined as a favorable superposition composite (PV maxima within 400 km of
TC center) for TC intensification based on the criteria established by Hanley et al. 2001.
Figure 3a shows the horizontal plot of PV on the 330 K isentropic surface at the time
above with values of PV above 4 PVU at the TC center and a sharp gradient in PV
extending above 1.5 PVU close to the TC’s PV anomaly. The horizontal winds overlaid
on this plot clearly show the movement of high PV air from the base of the trough
advecting into the core of the TC producing a constructive interference effect detailed in
section 2. The vertical cross section plot (sliced at 40N) shows an arm like extension of
PV associated with the trough containing values at higher levels above 5 PVU moving
towards the center and a longer protrusion with values between 1 and 1.5 PVU located
close to the storm at around 600 mb. The TC is shown to be more intense than the
previous time period with large values of PV (between 4 and 5 PVU) at higher levels in
the atmosphere yet the entire core of the PV anomaly remains well intact and matches the
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scale of the trough. Contours of potential temperature reveal a distinct warm core
structure throughout the center of the vortex with isentropes moving apart in the lower
portions of the atmosphere within the TC’s PV anomaly. This observation indicates the
TC was experiencing an increase in relative vorticity from conservation of momentum
arguments that allowed, among other processes, for the rapid deepening (14 mb pressure
drop in six hours) of Michael during and just after the time period of analysis. Figure 3c
shows that the center of Michael is within a zone of low wind shear at this time, but is on
the cusp of an extremely large gradient in shear associated with the approach of the
trough. In addition, both the horizontal winds overlaid on the PV plot and the vertical
wind shear display stronger winds to the north and northeast of the TC indicating that the
outflow anticyclone is becoming enhanced producing trough thinning. This is a perfect
example of scale matching that enabled the trough to provide the TC with the necessary
benefits without letting the detrimental effects of wind shear overwhelm the storm.
Figure 3d explains that the TC is still within a good source region of moisture in the mid
levels to sustain convection and avoid the negative impacts of dry air intrusions.
At 0000 UTC 20 October, the MUTT has begun to “drive” the evolution of Michael,
which leads into the progression of the ET process. Figure 4a displays the horizontal plot
of PV on the 330 K isentropic surface overlaid with the horizontal winds. The distance
of the trough’s PV anomaly from the TC center is less than 100 km, but the interaction is
difficult to discern as some of the high PV air from the trough has begun to mesh with the
PV from the TC. The maximum PV of the TC has gone down from the previous time to
roughly 3 PVU, but the anomaly has a larger diameter due to the wind field expansion in
cases of ET (Hart 2005, personal communication). A large gradient in the PV field of the
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trough exists to the southwest of the storm where high PV air has begun to wrap around
the storm a further indication of ET with maximum values at around 8 PVU (Jones et al.
2003). Figure 4b displays the vertical cross section (sliced at 48N) of PV with a rather
large region of air greater than 1.5 PVU (maximum of ~3 PVU) associated with the TC
and a sharp lobe of PV greater than 7 PVU protruding into the middle part of the
atmosphere. Potential temperature contours indicate that the vortex has begun to take on
slight cold core structure reminiscent of extra-tropical systems although the densest cold
air still remains within the narrow zone of the trough. Figure 4c shows that Michael is
experiencing larger values of vertical shear at this time around 30 m/s while Figure 4d
displays the movement of dry air associated with the trough. Strong wind magnitudes on
the horizontal PV plot across the center and to the northeast of Michael indicates ascent
along the 330 K surface and when coupled with the movement of the storm into a
baroclinic zone with increased vertical wind shear, may imply warm frontogenesis,
although further study is needed (Jones et al. 2003).
Finally, at 1200 UTC 20 October the horizontal plot of PV along the 325 K isentropic
surface in Figure 5a displays a more pronounced wrapping of the PV anomalies with an
increased asymmetric structure. A large core of PV around 7 PVU is collocated with the
model’s location of ET Michael at this time along with the generation of a cold front
trailing down from the center of Michael indicated by the thin zone of PV around 6 PVU
to the south and southwest of the storm. The horizontal winds surrounding the storm
show an area of ascent along the 325 K surface to the northeast of Michael and descent to
the southwest of the storm, which would correspond to areas of warm and cold
frontogenesis, respectively if frontogenesis functions were analyzed in more detail.
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However, GOES infrared imagery at this time period (Figure 6) clearly shows the
development of cold and warm frontal features associated with the ET process of
Michael. The vertical cross section (sliced at 51N) of PV shows a distinctly asymmetric
cyclone with large values of PV above 5 PVU pushing down into the storm as the
tropopause descends lower in the atmosphere. Although there is a slight indication of a
warm core especially near the surface, the majority of the cyclone at this point is cold
core in nature throughout the troposphere.
Figure 5c shows that the wind shear has
begun to subside near the center of the storm although there are higher values with a large
gradient in shear off to the east. The long extension of dry air associated with the trough
shows up well in Figure 5d as this air continues to wrap around the cyclone and hinder
the growth of convection.
5. Conclusions
The Midlatitude Upper Tropospheric Trough (MUTT) interaction with the ExtraTropical Transition (ET) of Hurricane Michael (17-19 October 2000) from both a
synoptic and dynamic perspective was shown to be a rather multifaceted event. The use
of full PV in the diagnoses of a MUTT interaction and ET process proved beneficial for
the analysis of storm structure in various phases. In particular, the storm composites
identified by Hanley et al. (2001) seemed to fit rather well in this study, which further
improves their utility for identification of trough interactions from both a research and
forecasting perspective. PV thinking helped to elucidate the reasoning for Michael’s 14
mb pressure drop in only six hours as a MUTT approached the TC center. PV seemed
particularly useful in explaining the ET process as high PV air wrapped around Michael
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and began to interact with the baroclinic environment. Knowledge of this process will
certainly help out the author in his work on a Master’s Thesis involving the structural
change of mid-latitude frontal systems as they merge with transitioning TCs.
Acknowledgements. I thank Dr. Robert Hart for his countless discussions and patience in a
Tropical II class that proved to strengthen my interest and knowledge in a subject I certainly hope
to be involved with in some way for my career. The author also wishes to acknowledge use of
the Ferret program for analysis and graphics in this paper. Ferret is a product of NOAA's Pacific
Marine Environmental Laboratory (Information is available at www.ferret.noaa.gov).
REFERENCES
Abraham, J., J. W. Strapp, C. Fogarty, and M. Wolde, 2004: Extratropical transition of
hurricane Michael. Bull. Amer. Meteor. Soc.,
95, 1323-1339.
Hanley, D., J. Molinari, and D. Keyser, 2001: A composite study of the interaction
between tropical cyclones and upper-tropospheric troughs. Mon. Wea. Rev., 129,
2570-2584.
_____, 2002: The evolution of a hurricane-trough interaction from a satellite perspective.
Wea. Forecasting, 17, 916-926.
Jones, S.C., and co-authors, 2003: The extratropical transition of tropical cyclones:
forecast challenges, current understanding, and future directions. Wea.
Forecasting, 18, 1052-1092.
Molinari, J, S. Skubis, and D. Vollaro, 1995: Exernal influences on hurricane intensity.
part III: potential vorticity structure. J. Atmos. Sci., 52, 3593-3606.
____, ____, ____, F. Alsheimer, and H.E. Willoughby, 1998: Potential vorticity analysis
of tropical cyclone intensification. J. Atmos. Sci., 55, 2632-2644.
Stewart, S.R., 2000: Tropical cyclone report hurricane Michael 17-19 October 2000.
NCEP Rep., 13 pp. [Available online at http://www.nhc.noaa.gov/2000michael.html.]
WMO, 1995: Global perspectives on tropical cyclones. WMO Technical Document. 693
pp.
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TABLES
Table 1. Comparison of rain rates retrieved from SSM/I satellites during the times of
overpass of Michael's center for the area averages indicated. Also shown is the
distance of the TC center from the Potential Vorticity Anomaly (PVA = 1.5 PVU) for
each overpass.
TIME (UTC)
TC CENTER(°N,°W)*
Rain Rate (mm/hr)
DISTANCE FROM PVA (km)
18-Oct-2000
148
1100
1342
1418
2218
(30.50,71.00)
(31.50,70.50)
(31.75,70.25)
(32.00,70.00)
(33.75,68.50)
Center|1°x1°|2°x2°|3°x3°
11.80|8.93|5.56|3.24
21.20|15.16|11.44|7.34
6.70|11.35|9.05|5.52
20.50|14.15|9.38|5.33
3.00|15.48|12.37|8.35
~705
~598
~564
~557
~456
19-Oct-2000
106
136
1042
1324
(34.50,67.50)
(34.75,67.25)
(39.00,62.50)
(40.75,60.75)
10.50 |13.34|10.50|7.54
23.10|13.31|9.90|6.67
25.00|11.83|8.62|7.12
1.10|2.04|3.16|4.87
~424
~419
~337
~299
(41.25,60.50)
1.30|2.36|3.45|4.79
~288
1400
*Closest data point to TC center from NHC since SSM/I data has 0.25° resolution.
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FIGURES
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Figure 1. GOES 8 water vapor imagery at 12:15 UTC 19th October 2000.
Figure 2a. Horizontal plot of PV on the 335 K isentropic
surface for the time period indicated in PVU with 0.5 PVU
increment. Horizontal wind vectors along the same surface are
overlaid with reference vector in m/s. Model TC center
indicated by the hurricane symbol.
Figure 2b. Vertical cross section of PV in the x-z plane for
the time period indicated in PVU with increment of 0.5 PVU
and 1.5 PVU (nominal tropopause) darkened. Contours of
potential temperature are overlaid in K with increment every
5K. Latitude of slice indicated at top of plot.
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QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Figure 2c. Vertical wind shear in 200 - 850 mb layer
overlaid with streamlines at time period indicated. Values
are contoured every 5 m/s with streamline reference in m/s.
Figure 3a. Horizontal plot of PV on the 330 K isentropic surface
for the time period indicated in PVU with 0.5 PVU increment.
Horizontal wind vectors along the same surface are overlaid
with reference vector in m/s. Model TC center indicated by the
hurricane symbol.
Figure 2d. Relative Humidity at 700 mb contoured
every 10 % for the time period indicated.
Figure 3b. Vertical cross section of PV in the x-z plane for the
time period indicated in PVU with increment of 0.5 PVU and
1.5 PVU (nominal tropopause) darkened. Contours of potential
temperature are overlaid in K with increment every 5K.
Latitude of slice indicated at top of plot.
Guimond
Tropical Meteorology II
Figure 3c. Vertical wind shear in 200 - 850 mb layer
overlaid with streamlines at time period indicated. Values
are plotted every 5 m/s with streamline reference in m/s.
19
Figure 3d. Relative Humidity at 700 mb contoured every
10 % for the time period indicated.
Figure 4a. Horizontal plot of PV on the 330 K isentropic surface
for the time period indicated in PVU with 0.5 PVU increment.
Horizontal wind vectors along the same surface are overlaid
with reference vector in m/s. Model TC center indicated by the
hurricane symbol.
Figure 4b. Vertical
the time period indica
and 1.5 PVU (nomin
potential temperature
5K. Latitude of slice i
Guimond
Tropical Meteorology II
Figure 4c. Vertical wind shear in 200 - 850 mb layer
overlaid with streamlines at time period indicated. Values
are plotted every 5 m/s with streamline reference in m/s.
Figure 5a. Horizontal plot of PV on the 325 K isentropic
surface for the time period indicated in PVU with 0.5 PVU
increment. Horizontal wind vectors along the same surface are
overlaid with reference vector in m/s. Model TC center
indicated by the hurricane symbol.
20
Figure 4d. Relative Humidity at 700 mb contoured
every 10 % for the time period indicated.
Figure 5b. Vertical cross section of PV in the x-z plane for the
time period indicated in PVU with increment of 0.5 PVU and
1.5 PVU (nominal tropopause) darkened. Contours of
potential temperature are overlaid in K with increment every
5K. Latitude of slice indicated at top of plot.
Guimond
Tropical Meteorology II
Figure 5c. Vertical wind shear in 200 - 850 mb layer
overlaid with streamlines at time period indicated. Values
are plotted every 5 m/s with streamline reference in m/s.
21
Figure 5d. Relative Humidity at 700 mb contoured
every 10 % for the time period indicated.
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Figure 6. GOES 8 infrared imagery at 12:15 UTC 20th October 2000.