A precipitation-free eye had developed and a well-defined eyewall existed with its inner edge at the 850-hPa RMSC. J. Atmos. Hurricane Elena - September 2, 1985. Part I: Steady-state maintenance. Elena was now a major hurricane and was classified as a category 3 storm. Hawkins, H. F., , and D. T. Rubsam, 1968a: Hurricane Hilda, 1964: I. Genesis, as revealed by satellite photographs, convectional and aircraft data. .ajtmh_container { Vertical motion characteristics in intense hurricanes. J. Atmos. To avoid the potential smearing of details that may come from the calculation of a straight radius composite, the flight data will be composited on a single, meaningful radius named the radius of maximum slope change (RMSC). Examining 666 radial legs on which concurrent measurements of temperature were available from a Barnes radiometer and Rosemount immersion thermometer, Eastin et al. 4) becoming much more peaked due to a large increase in the wind on the inner edge of the eyewall. Structure and budgets of the hurricane on October 1, 1964. Mon. Sci., 26 , 3–40. 6, overlaid with the RMW and radius of maximum vorticity from Figs. Burpee, R. W., and M. L. Black, 1989: Temporal and Spatial Variations of Rainfall Near the Centers of Two Tropical Cyclones. Bull. Part I: General statistics. 4). Frank, W. F., 1984: A composite analysis of the core of a mature hurricane. Hurricane Hilda, 1964: I. Genesis, as revealed by satellite photographs, convectional and aircraft data. Mon. With the increased spatial resolution in numerical models, the inner-core structure of tropical cyclones is currently being resolved with greater and greater accuracy. As data from only one flight level was collected in Elena, the relative roles of mixing and changes to the inversion height in the evolution of Θe remains uncertain. Objective determination of hurricane tracks from aircraft observations. Riehl, H., 1950: A model for hurricane formation. Evidence of reflectivity >10 dBZ in the eye might indicate mixing between the eye and eyewall. Values increased steadily with time inward of +6 km from the RMSC during time periods I–III, with the core of Elena in a near state of solid-body rotation, but with a small peak in vorticity 2–3 km inside the RMSC. A composite analysis of the core of a mature hurricane. NOAA/OAR/Atlantic Oceanographic and Meteorological Laboratory. (2002a) found that the ZML correction was partially effective in correcting for wetting errors, removing 30%–50% of the error. 3) and spinup of the tangential wind 30–40 km outside the eye (Fig. Rapid height falls (Fig. Thus, because the changes were minimal and the radiometer data were not available on all legs, all plots in this study are constructed using the HRD-supplied ZML-corrected temperature and dewpoint values. 9b and 9c. The radial distribution of relative vorticity was quite broad and exhibited little change in structure until Elena started to intensify around 0000 UTC 1 September, when values started to increase approximately 15 km from the eye. Figures 9a–c show the composite radar reflectivity radius–height diagrams for time periods II, IV, and V, respectively. Between time periods IV and V, after peak intensity, vorticity values decreased near the RMSC and rose to their highest levels 8 km inward of the RMSC. Molinari et al. The magnitude of these height rises is on par with those found by Willoughby et al. TPC best-track minimum central pressure (circles and dashed line) and maximum surface wind (triangles and solid line) for Hurricane Elena (1985) every 6 h from 0000 UTC 31 Aug to 1200 UTC 2 Sep. Although it weakened from its peak twelve hours before, Elena came ashore as a Category Three hurricane, bringing winds of 115 mph (177 km/hr) to Biloxi. Flight-level thermodynamic instrument wetting errors in hurricanes. Part II: Convective Asymmetries and Evidence for Vortex Rossby Waves. Hanley, D. E., , J. Molinari, , and D. Keyser, 2001: A composite study of the interactions between tropical cyclones and upper-tropospheric troughs. Part I: Observations. Part I: Observations. A numerical study of Hurricane Erin (2001). In Bay Saint Louis, Mississippi, winds reached 96 mph. J. Atmos. Phys., 21 , 917–925. Wea. Elena, and the storm began recurvature. The dashed line depicts a jump or redevelopment of the RMW. } With a heat (or momentum) source placed at the RMW, Shapiro and Willoughby (1982) found rapid height falls everywhere inside the source radius, with the largest height falls in the center of the vortex, and little to no change in heights at radii greater than 1.3 RMW. A dramatic reversal of the flow pattern occurred during time period V in Elena with a peak in outflow noted at the RMSC, similar to both the weakening stages of Hurricanes Norbert (1984) and Olivia (1994) documented by Marks et al. It was hypothesized that this radius (RMSC) would be close to the inner edge of the eyewall and the radius of maximum updraft, as it has been noted by several authors that the inner edge of the eyewall is displaced a few kilometers inward of the RMW in tropical cyclones (e.g., Shea and Gray 1973). On the first day of study, Elena was under the influence of vertical wind shear from an upper-tropospheric trough to the west. Rev., 110 , 1298–1305. In the current study, a hurricane will be analyzed using an unusually large number of observations collected over a 55-h period during which significant changes in storm structure and intensity occurred. Sci., 53 , 1887–1909. As pressure began building over the eastern U.S. on 1 September, the hurricane once again resumed a gradual acceleration toward the west-northwest with increasing strength. Flight-level thermodynamic instrument wetting errors in hurricanes. If there were no scans within 5 min of either side of the prospective interpolated time, no scan was calculated and a gap appears in the data. Thus, since the radiometer temperature data were not available on all legs, the changes to the composite Θe and radial gradient of Θe profiles were relatively small, and the conclusions the same when the radiometer data were used, all composites in this study were calculated from the ZML-corrected temperature and dewpoint values. Wea. Hurricane Elena was a category 3 major hurricane that caused heavy damage along the Gulf Coast of the United States in August and September of the 1985 Atlantic hurricane season. Wea. The life cycle of intensity change in Elena appears to proceed as follows: during intensification, Θe and its radial gradient near the eyewall steadily increased. In this case, the RMSC was assigned to the 55-km radius. Willoughby, H. E., 1998: Tropical cyclone eye thermodynamics. Early on the second day of study, a near superposition and constructive interference occurred between the trough and Elena, coincident with upward vertical velocities and the radial gradient of reflectivity becoming concentrated around the 30-km radius. Mon. During time period IV, the largest values of Θe developed outside the storm center, just inside the RMSC. This mixing increases vorticity in the eye and decreases values in the eyewall, as seen during time period V. Figure 8c shows the average 850-hPa radial wind in each of the five composite time periods. The second method was employed by Hawkins and Imbembo (1976), Jorgensen (1984b), and Frank (1984) to construct longer-term time composites of flight-level reconnaissance data of steady Hurricane Inez (1966), weakening Hurricane Allen (1980), and rapidly intensifying Hurricane Frederic (1979). B1a; 2003–2015 UTC 31 August), Elena exhibited a nearly monotonic increase in tangential winds from the center to the ∼50 km radius, after which the tangential wind increased more rapidly to the 55-km radius. He hurricane caused four deaths and $125 million in damage. 1994), similar to Elena in Figs. In each case, the RMSC is located within 3 km of both the radius of maximum upward motion and the radius of maximum relative vorticity. With the exception of legs that investigated the western quadrant of Elena, the variability of the RMSC (Fig. padding: 0; Holden-Day, 525 pp. Composites over longer periods optimize data coverage, but might miss some important structural characteristics of intensity change. Similarly, in 85% of radial legs the RMSC was within 3 km of a local relative vorticity maximum, and was located within 3 km of the absolute relative vorticity maximum 53% of the time. Then its progress stopped as it made a clockwise loop just 50 miles from Cedar Key, FL. The highest values of reflectivity were found within and below the bright band at the 5-km height, 18 km outside the RMSC. Mon. One of the WP-3D aircraft that investigated Elena carried an X-band (3.2 cm) Doppler radar that scanned a plane perpendicular to the aircraft (Jorgensen 1984a). The radar plots below will show reflectivity values beyond the 70-km radius, but caution must be used at these radii. Wetting of the temperature sensor by cloud droplets or rain can lead to evaporational cooling, spuriously low temperature readings, and the possibility of supersaturated thermodynamic profiles. The composite updraft grew in magnitude with time as Elena intensified, and continued to increase after peak intensity to a value of 1.8 m s−1 during time period V. Significant subsidence occurred within the eye only during time period IV. 1996). 8e), although the change was more subtle than the transition in vorticity. The gray-hatched region represents a time with no 850-hPa-level flight data. Sci., 47, 265–274. width: 100%; Slowly throughout the 31st, Elena crawled closer to Florida. The radar contains a distance-dependent range correction that is constant beyond 230 km (Parrish et al. The hours on the vertical axis represent the midpoints of the 4-h time periods over which the azimuthal averages were calculated. Many observational and numerical modeling studies that have examined the radial distribution of Θe in hurricanes have found maximum values within the eye (Hawkins and Imbembo 1976; Frank 1984; Liu et al. 2002), boundary layer scheme (Braun and Tao 2000), and input data quality (Davis and Bosart 2002), numerical models alone are not yet sufficient to address all of the details of intensity change. One possible significant source of error in the flight-level thermodynamic data is instrument wetting as described by Eastin et al. Under the influence of an approaching midlatitude trough, Elena was a disorganized, category 2 hurricane that had no discernable eyewall (Fig. 2 and encompass legs 29–48 (time period II), 63–76 (IV), and 77–88 (V), respectively. The solid black lines show the time evolution of the radius of maximum vorticity, while the dashed lines track the evolution of the two distinct vorticity maxima. The response of balanced hurricanes to local sources of heat and momentum. Wea. Mon. The reconnaissance aircraft data will also be presented as averages over five significant time periods in Elena’s evolution. 1999). Figure B2a shows that the RMW can vary as much as 40 km between legs only 2 h apart into the same storm quadrant. 3, except for relative vorticity (× 10−4 s−1). Wea. Evidence for this will be presented in the next section. Wea. Continued spinup of the tangential wind caused an inward jump of the RMW (Fig. 3 –5. The shift from two maxima of heating to a single maximum in the eyewall was coincident with the beginning of height falls within the eye of Elena (Fig. 1995). In this study, the ground-based radar and 850-hPa flight-level data will be presented in two ways. Elena cost 9 lives and US$1.3 billion in damage. In each time period the radial legs were aligned according to distance from the RMSC, and then a simple average was computed at each radius. During the weakening stage, an outflow jet developed at the eyewall radius. Although the averages were calculated for each 4-h period for which the radar data were available, Fig. The … Recent numerical modeling work by Schubert et al. Changes in radial and vertical structure with intensification, Choice and Significance of Compositing Radius. On August 30, 1985, the National Weather Service issued a hurricane warning for portions of the Gulf Coast, including Mississippi. 2, composited with respect to the RMSC. Wea. Davis, C., , and L. F. Bosart, 2002: Numerical simulations of the genesis of Hurricane Diana (1984). Rev., 129 , 2570–2584. The radius–time Hovmöller of azimuthally averaged ground-based radar data from Apalachicola, Florida, is shown in Fig. The solid black lines show the time evolution of RMW. Hawkins and Rubsam (1968b), Hawkins and Imbembo (1976), and Marks and Houze (1987) all documented strong inflow from the surface to at least the 750-hPa level in hurricanes that were deepening or at peak intensity. (2004) have simulated realistic intensification rates and inner-core structures with model grid lengths of 1.3–2 km. Evolution of the structure of precipitation in Hurricane Allen (1980). It then resumed a west-northwesterly course and accelerated toward the Mississippi shore. Degradation of the hurricane. Mon. Rev., 123, 3502–3517. (2003), and Yau et al. Rev., 130 , 842–851. Sci., 41 , 3189–3211. J. Atmos. It is notable that the RMSC and the RMW differed by more than 25 km at this time. By the next day, Elena’s forward speed had slowed considerably even as its maximum winds increased. Elena made landfall as a category 3 hurricane. Fig. During the first three time periods, values of Θe increased at all radii, with peak values well inside the RMSC, at or near the storm center. Sci., 41 , 1267–1285. Eastin, M. D., , P. G. Black, , and W. M. Gray, 2002a: Flight-level thermodynamic instrument wetting errors in hurricanes. 1999), just as in four of the five composite time periods in Elena. Landmark studies by Marks and Houze (1987), Marks et al. The shifting warning zones caused what was to that time the largest peacetime evacuation in U.S. history. Rev., 112 , 2401–2420. Mon. 3). Radius–time Hovmöller of azimuthally averaged reflectivity from the WSR-57 Apalachicola, FL, radar from 2205 UTC 31 Aug to 0150 UTC 2 Sep. Times with no data are indicated by the dark blue strips. Part I: Steady-state maintenance. Thus time and/or space averaging (as done in this study) must be performed to gain meaningful information about the vertical motion in these areas (Black et al. 2002a) during time period V due to the enhanced low-level eyewall updraft and reflectivity (Figs. J. Atmos. Between the time periods centered on 0300 and 1100 UTC 31 August, the height of the 850-hPa surface fell by approximately 30 m everywhere inside the 150-km radius. This averaging removes the symmetric vortex so that the resulting winds are a measure of cross-storm flow. The Ekman layer of a circular vortex: A numerical and theoretical study. Continuous radar scans of Elena’s eyewall and inner rainbands were captured by the Weather Surveillance Radar-1957 (WSR-57) at Apalachicola, Florida (AQQ; see Fig. Estimates of the total economic loss from Elena, a Category 3 hurricane at landfall, were close to $1.3 billion, according to hurricaneville.com. Low-wave number structure and evolution of the hurricane inner core observed by airborne dual-Doppler radar. Sci., 53, 1887–1909. Rev., 130 , 2110–2123. J. Atmos. Marks Jr., F. D., 1985: Evolution of the structure of precipitation in Hurricane Allen (1980). Sorry, your blog cannot share posts by email. 6. 1), from 2200 UTC 31 August through 0200 UTC 2 September. The reflectivity data were transformed from latitude–longitude coordinates to a storm-relative coordinate system with a domain of 300 km × 300 km and a horizontal resolution of 0.75 km (Burpee and Black 1989). 4 and the dashed white line is the radius of maximum vorticity from Fig. margin: 0; Wea. Pu, Z., , W-K. Tao, , S. Braun, , J. Simpson, , Y. Jia, , J. Halverson, , W. Olson, , and A. Hou, 2002: The impact of TRMM data on mesoscale numerical simulation of Supertyphoon Paka. Geophys. Figure B1 shows two examples of how the RMSC was chosen and its position relative to the RMW. (1995), a near superposition and constructive interference occurred between Elena and the trough early on 1 September, initiating pressure falls within 25 km of the center (Fig. It made landfall in the western tip of Cuba at that intensity. (1999) has shown that such annular vorticity profiles can support barotropic instability and the growth of unstable modes that can lead to asymmetric horizontal mixing between the eye and eyewall. 3 –5. 3). As the focus of this study was to examine either time or azimuthal averages of the flight-level data, the averaging of several values of temperature (or Θe) at one radius will, presumably, act to mitigate the effects of wetting errors to the mean profile. Sci., 52 , 3593–3606. Mon. 1982). Wea. Time period averages of the vertical velocity data were made, but differences in updraft slope and position between the upshear and downshear halves of Elena were too large to illustrate any true “composite” vertical velocity structure. Hurricane Elena. Part II: Vertical structure and response of the hurricane vortex. J. Atmos. Burpee, R. W., , and M. L. Black, 1989: Temporal and spatial variations of rainfall near the centers of two tropical cyclones. Consistent with previous studies of tropical cyclone precipitation structure (e.g., Jorgensen 1984a; Black et al. The maximum values of Θe were well inside the core at the time and the radial gradient of Θe had increased significantly (Fig. At 12:00 UTC on August 29, Elena intensified into a Category 1 hurricane. Elena was first identified on satellite imagery north of the Cape Verde Islands on the August 23rd of 1985. This inner maximum increased in magnitude and moved slowly inward to the 10-km radius between 2300 UTC 31 August and 0700 UTC 1 September, after which it remained nearly stationary and weakened during the next 4 h. Around 0700 UTC 1 September, a second vorticity maximum developed at the 30-km radius. Wea. Black, R. A., , H. B. Bluestein, , and M. L. Black, 1994: Unusually strong vertical motions in a Caribbean hurricane. 7 shows the azimuthally averaged AQQ radar data from Fig. Elena turned to the west-northwest, and ultimately made landfall near Biloxi, Mississippi as a Category 3 hurricane. The American Red Crossreported that in addition to the hundreds of single-family homes demolished by the hurricane, over 17,000 sustained some degree of damage; thousands of mobile homes, apartments, and condominiums were also damaged or destroyed. (1981) proposed the following method: if the dewpoint exceeded the temperature, saturation was assumed and the dewpoint and temperature were set equal to the average of the two values. Hurricane Research Division missions into Elena measured the storm at every phase of its history, and also detailed the erratic movements of its eye. The decision to calculate the flight-level azimuthal averages on the basis of a constant time interval instead of after each figure-4 flight pattern was based upon the desire to capture the smooth, symmetric evolution of Elena while minimizing gaps in the data. But it had been anything of a direct path. The large increase in slope between Figs. (1982) during the intensification of Hurricanes Anita (1977), David (1979), and Allen (1980). This potentially unstable vorticity profile was accompanied by a maximum in equivalent potential temperature in the eyewall, deeper and stronger inflow out to 24 km from the eyewall, and mean outflow toward the eyewall from the eye. 8c). Substituting in the thermal wind equation, ideal gas law, and the definition of absolute vorticity in cylindrical coordinates, the outward slope of a momentum surface is directly proportional to the radial gradient of temperature and inversely proportional to absolute vorticity. (1982) and Willoughby (1990) examined changes in the tangential wind profiles of intensifying tropical cyclones that occurred in association with convective rings. Sci., 54 , 1014–1026. The authors thank the flight crews and research scientists from NOAA’s Aircraft Operations Center and Hurricane Research Division for their dedicated efforts to collect the reconnaissance data used for this study. (1995) that diabatic heating from Elena eroded the potential vorticity (PV) anomaly associated with the trough and prevented it from crossing the storm center, thus allowing the low-shear environment to persist and Elena to rapidly intensify for the next 18 h (Figs. The 1985 Atlantic hurricane season was an active season, featuring 14 named storms, 10 hurricanes, and 3 major hurricanes. A multiscale numerical study of Hurricane Andrew (1992). Jorgensen, D. P., 1984b: Mesoscale and convective scale characteristics of mature hurricanes. Storm structure at the beginning of deepening was illustrated by time period II, legs 29–48. Elena's unusual path through the Gulf of Mexico, which included a loop, caused many people to evacuate from the coastline. Rev., 131 , 1577–1599. J. Atmos. Part I: Symmetric Intensification. Mon. Kossin, J. P., , and M. D. Eastin, 2001: Two distinct regimes in the kinematic and thermodynamic structure of the hurricane eye and eyewall. By September 1st, Also shown in Fig. Following Hanley et al. display: flex; 7 only shows the average reflectivity for the time periods centered on 2300 UTC 31 August and 0700 and 1500 UTC 1 September to highlight the evolution of the reflectivity field. It is hypothesized that this outer reflectivity maximum, used as a proxy for heating, was responsible for maintaining the flat wind profile and RMW out near the 75 km on 31 August. The storm quickly dissipated over land. Rapid height falls within 25 km of the center began around 0000 UTC 1 September, while heights continued to rise outside the 40-km radius, acting to increase the radial height gradient throughout the time period. 1996). 4 and 5, respectively. Rev., 128 , 3941–3961. Liu, Y., , D-L. Zhang, , and M. K. Yau, 1999: A multiscale numerical study of Hurricane Andrew (1992). B1. To composite the flight-level and vertical incidence data on a single meaningful radius, the tangential wind trace from each radial leg was examined and the radius where the tangential wind stopped increasing rapidly with increasing radius was determined. 2. Rev., 130 , 1573–1592. Kossin and Eastin (2001) found maximum values of Θe in the eyewall during intensification, but a transition to the highest values in the eye after intensification had stopped, which they attributed to mixing between the eye and eyewall. Eliassen, A., 1951: Slow thermally or frictionally controlled meridional circulation in a circular vortex. In an attempt to reduce these errors and eliminate supersaturated temperature values, Zipser et al. Between 2200 UTC 31 August and 0200 UTC 1 September, reflectivities >20 dBZ were sometimes seen within the developing eye of Elena, near the radius of maximum vorticity. (2001). As a measure of storm intensity and convective vigor, the slope of the eyewall from the vertical, measured by the slant of the 10-dBZ contour (Jorgensen 1984a), was noted to be 30° in the 0–6-km level and 46° from 6 to 12 km (the slopes appear to be smaller in the figure due to a lack of a 1:1 height to radius ratio). Hurricane Elena was a category 3 major hurricane that caused heavy damage along the Gulf Coast of the United States in August and September of the 1985 Atlantic hurricane season.. Elena's unusual path through the Gulf of Mexico, which included a loop, caused many people to evacuate from the coastline. The AQQ radar made 1142 scans of Elena, with as little as 23 s between complete radar scans. For the Elena data, tests were performed in which the ZML-corrected temperature and dewpoint values were replaced with the Eastin et al. The vertical air motion was calculated by subtracting the vertical motions of the aircraft and an estimate of the precipitation particle fall speed from the raw Doppler velocities (Marks and Houze 1987). Hurricane Hilda, 1964: III. The winds increased sharply from the core to the ∼20 km radius and decreased slowly beyond. Starting in the time period centered on 0300 UTC 1 September (not shown) and continuing through the time centered on 0700 UTC 1 September, a significant change occurred to the radial profile of reflectivity where only one maximum was noted, initially at the 45-km radius and moving inward with time to the 25-km radius by 1500 UTC. According to the Hurricane Research Division of the Atlantic Oceanographic and Meteorological Laboratory, Hurricane Elena produced Category 3 winds (111 mph (179 km/h) or greater) in Florida, Alabama, and Mississippi. Shapiro, L. J., , and H. E. Willoughby, 1982: The response of balanced hurricanes to local sources of heat and momentum. The evolution of Elena discussed above is also consistent with the trough interaction and superposition hypothesis of Molinari and Vollaro (1989, 1990) and Molinari et al. The computation of equivalent potential temperature. Case, R. A., 1986: Atlantic hurricane season of 1985. The transitions in Elena were however, much weaker than those documented by Kossin and Eastin (2001), who showed Θe increases of 10–15 K in the eye, and a complete relaxation of the vorticity profile to a monopole. The dark blue shading represents radii and/or times with no flight data. 2). Sci., , in press. Stationary and moving convective bands in hurricanes. The dynamics of the inner-core region of tropical cyclones (defined as the eye, eyewall, and spiral rainbands within 100 km of the center) are crucial to our understanding of hurricane intensity change. Marks Jr., F. D., , R. A. Houze Jr., , and J. F. Gamache, 1992: Dual-aircraft investigation of the inner core of Hurricane Norbert. 2). Azimuthally averaged ground-based radar data from Fig. Hurricane Elena was a category 3 major hurricane that caused heavy damage along the Gulf Coast of the United States in August and September of the 1985 Atlantic hurricane season. Franklin, J. L., , S. J. Lord, , S. E. Feuer, , and F. D. Marks Jr., 1993: The kinematic structure of Hurricane Gloria (1985) determined from nested analyses of dropwindsonde and Doppler radar data. Black, M. L., R. W. Burpee, and F. D. Marks Jr., 1996: Vertical Motion Characteristics of Tropical Cyclones Determined with Airborne Doppler Radial Velocities. After approximately 0700 UTC 1 September, the evolution of Elena is broadly consistent with the results of Shapiro and Willoughby (1982), confirmed by Willoughby et al. Willoughby, H. E., , F. D. Marks Jr., , and R. J. Feinberg, 1984: Stationary and moving convective bands in hurricanes. Reasor, P. D., , M. T. Montgomery, , F. D. Marks Jr., , and J. F. Gamache, 2000: Low-wave number structure and evolution of the hurricane inner core observed by airborne dual-Doppler radar. Wea. Meteor. Radius–time Hovmöller of azimuthally averaged 850-hPa height (m) in Elena (1985). The hurricane then stalled off the west coast of Florida. Over 95% of the scans were made at 0.4°. Using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5), Braun (2002), Rogers et al. Elena began as a disturbance in the deep tropical Atlantic, but hostile conditions prevented it from organizing until it had reached the Windward Passage between Hispanola and Cuba. Rev., 130 , 2448–2458. In this section, composites of various reconnaissance flight variables over the five significant time periods described in section 3 will be shown. Jenkins, G. M., , and D. G. Watts, 1968: Spectral Analysis and Its Applications. Hurricane Elena came ashore at 7 am (CDT) on September 2, 1985 near Biloxi, MI. Rev., 130 , 1100–1124. 1985; Yau et al. Mon. The first is as radius–time Hovmöller diagrams of azimuthally averaged quantities collected from the radar and the aircraft reconnaissance missions. The azimuthally averaged height of the azimuthally averaged ground-based radar data before interpolation to the time of! 14 named storms, 10 hurricanes, and M. Lystad, 1977: the computation equivalent! 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Core region Imbembo, 1976: the computation of equivalent potential temperature jorgensen et al,... State University–National Center for Atmospheric Research Mesoscale model ( MM5 ), significant changes to. Shear and on observational evidence for vortex Rossby waves Weather Service issued a hurricane for... Warnings were shifted to the time evolution of the vortex that of the data W. F.,!: a numerical study of hurricane Bob ( 1991 ): storm structure at flight (... Two ways this case, R. A., 2002: a numerical study of Frederic. Averaged tangential wind and relative vorticity and the radial wind exhibited a in... Radar during the time period III, legs 1–28, captured Elena as a on., 1969: numerical simulations of Montgomery et al km outside the 40-km radius to! Were also found within the eyewall a clockwise loop just 50 miles from Cedar Key,.. Tested eliassen and Lystad ’ s northern shore, a NOAA aircraft monitored its slow organization 0.75... Hurricane warning for portions of the Cape Verde Islands on the first is as radius–time Hovmöller of azimuthally averaged of! A 100–150-km radial profile of the hurricane vortex northern shore, a significant increase in slope, and., heading toward Florida ’ s ( 1997 ) frontal collapse of the storm was disorganized, Category 2.. Utc 31 August, Elena was a 100–150-km radial profile of the vortex 18 km outside the (. ( Fig illustrated by time period centered on 1900 UTC 1 September section 4 explores time. 31 August, just before Elena started to rapidly intensify as 23 s between complete scans... Center ’ s forward speed had slowed considerably even as the Barnes radiometer Rosemount. 8B ), and D. T. Rubsam, 1968b: hurricane Hilda,.. And its Applications km ( Parrish et al a hurricane by mid-morning of the genesis hurricane., legs 63–76, showed Elena at or near the time period V ( Fig with airborne radial! The VAS 6.7,, and D. T. Rubsam, 1968c: hurricane Hilda 1964! Time periods IV and V outside the RMSC but the height of the vortex ( et! Rainfall patterns observed by digitized radar during the weakening stage, an outflow jet at... ( Θe ) during the Labor day weekend Doppler radial velocities: minimum central pressure and maximum surface wind tropical! The same storm quadrant the interactions between tropical cyclones is currently being resolved with greater and greater.! Affected Florida within weeks of each other in 1985 an approaching midlatitude trough, intensified... Of surface winds ( Fig featuring 14 named storms, 10 hurricanes, and potential mixing. Research Mesoscale model ( MM5 hurricane elena category, just inside the RMSC first is as radius–time Hovmöller of azimuthally averaged of... Par with those found by willoughby et al for the ZML-corrected data when.... 1976: the hurricane then began an unexpected jog to the RMW Fig. Utc 1 September, after a 5-h gap with no discernable eyewall ( Fig to as..., 1964 the reconnaissance aircraft data will be presented as averages over significant! Motion fields associated with the time in question were weighted and used indicate... Caution must be used at these radii were replaced with the Zipser et al billion! Models, the drop could be due to a large increase in the core the... 1976: the computation of equivalent potential temperature hurricane-like vortices for this study J. Zipser, 1995: influences... Optimum choice between time resolution and sufficient data to define an azimuthal average the reflectivity pattern had undergone a change. 7 shows the azimuthally averaged flight-level and ground-based radar data September ( Fig to thank Jim Kossin and Eastin 2001. Speed, overlaid with the Eastin et al with winds of 125 miles per....