DOCSLIB.ORG

A WSR-88D Assessment of Tropical Cyclone Outer Rainband Tornadoes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A WSR-88D Assessment of Tropical Cyclone Outer Rainband Tornadoes SEPTEMBER 1997 SPRATT ET AL. 479 A WSR-88D Assessment of Tropical Cyclone Outer Rainband Tornadoes SCOTT M. SPRATT AND DAVID W. S HARP NEXRAD Weather Service Of®ce, National Weather Service, Melbourne, Florida PAT WELSH AND AL SANDRIK NEXRAD Weather Service Of®ce, National Weather Service, Jacksonville, Florida FRANK ALSHEIMER AND CHARLIE PAXTON NEXRAD Weather Service Of®ce, National Weather Service, Tampa Bay, Florida (Manuscript received 5 January 1996, in ®nal form 15 April 1997) ABSTRACT As part of the National Weather Service (NWS) Modernization and Restructuring Program, WSR-88D (NE- XRAD) Doppler radar installation has been completed at each Weather Service Of®ce in Florida. Recently, this powerful new tool provided unique opportunities for Jacksonville, Tampa Bay, and Melbourne NEXRAD Weather Service Of®ce personnel to investigate tropical cyclone (TC) rainbands for evidence of tornadogenesis. This study provides a radar-based analysis of known tornadic mesocyclones associated with two mature tropical cyclones that were not landfalling in the vicinity of the tornado occurrence, namely, Tropical Storm Gordon (1994) and Hurricane Allison (1995). Based on successful NEXRAD sampling strategies, detailed analyses of storm-scale re¯ectivity and velocity signatures are conducted in the context of establishing preliminary critical criteria for use in the tornado detection and warning process. Important characteristics were found to include detection of discrete, small diameter .50 dBZ echos collocated with storm-relative rotational velocities of 6.5± 15ms21. Rotational features, although often subtle, were identi®able for an average of 30 min prior to tornado production, with total durations of 1±2 h. Near the time of tornado touchdown, the core diameter of the low- level circulation couplets contracted to approximately 1.85 km (1 n mi), leading to an associated increase of shear across the circulation to 0.010 s21 or greater. A comparison between the well-studied Great Plains tornadic supercell and the observed TC-tornado cells revealed a common trait of persistence. While the average depth of rotation associated with the TC-tornado cells (3.5 km) was much more shallow than their midwest counterparts, the ratio of depth of rotation to storm top were comparable. However, the shallow depth and weaker detectable rotation of the TC (tornadic) meso- cyclones greatly reduced the detection capability of the current WSR-88D mesocyclone algorithm when compared to identi®cation of traditional supercells. Based upon the analyzed data, the authors offer several recommendations to assist operational radar mete- orologists with the challenging task of detecting outer rainband tornadoes. Additionally, the authors propose a new WSR-88D scan strategy (volume coverage pattern, VCP) that would provide additional low-level slices in lieu of several current upper-elevation angles. This new VCP would facilitate improved vertical sampling at lower heights where TC mesoscale circulations are most likely to be detected. 1. Introduction centage, tropical cyclones landfalling from the Gulf of Mexico produce more tornadoes than Atlantic storms. In the United States, tornadoes account for as much This is also true for Florida events, where Hagemeyer as 10% of the total deaths associated with tropical cy- and Hodanish (1995) found that 87% of tornado-pro- clones (Novlan and Gray 1974). Most tropical cyclone ducing tropical cyclones have historically approached (TC) tornadoes occur within 24 h of landfall and are from the Gulf of Mexico, placing the state in the pre- favored within a sector 08±1208 in azimuth, relative to ferred sector. true north from the cyclone center (Hill et al. 1966; Gentry (1983) and Weiss (1987) found a bimodal Novlan and Gray 1974; Gentry 1983). By a large per- distribution of tropical cyclone tornadoes with respect to range from the cyclone center. ``Core'' tornadoes occur within inner rainbands or in the eyewall, while the optimum range for ``outer rainband'' tornadoes is Corresponding author address: Scott M. Spratt, National Weather Service, 421 Croton Road, Melbourne, FL 32935. 200±400 km from the center, but they can occur at even E-mail: [email protected] greater distances. Weiss (1987) found that more than q1997 American Meteorological Society 480 WEATHER AND FORECASTING VOLUME 12 74% of postlandfall tornado occurrences reported from largest contributing factor to the genesis of tornadic 1964 to 1983 were associated with outer band con- cells within tropical cyclones and that buoyant insta- vection, while in a study of Florida tornadoes asso- bility played only a minor role. In model simulations ciated with tropical cyclones between 1882 and 1994, of TC-spawned supercells, Weisman and McCaul Hagemeyer and Hodanish (1995) stated that 25 of 61 (1995) found that the upward dynamic pressure gra- cases involved tornadoes that occurred on the ``outer dient force contributed about three times as much to fringes of systems.'' It is at these greater distances from the updraft speed as buoyancy. Collectively, these the TC center, where the severe weather awareness may sources have served to raise the level of understanding not be high, that tornadoes could be the primary threat and anticipation of the TC-tornado threat through cli- (Weiss 1987; McCaul 1991). matological patterns, statistics, and buoyancy/shear as- On several occasions airborne Doppler radars aboard sessments. National Oceanic and Atmospheric Administration re- Even with an increased recognition of favorable syn- search aircraft have detected small-scale vortices (also optic-scale TC-tornado environments, many of these referred to as mesovorticies or mesocyclones) within tornadoes still occur without of®cial National Weather convective eyewall bands of intensifying strong hur- Service (NWS) warnings or with little (or negative) ricanes (Marks and Houze 1984; Black and Marks lead time. To increase warning skill, an improved un- 1991; Willoughby and Black 1996). Stewart and Lyons derstanding of storm-scale characteristics and radar in- (1996) more recently observed similar features during terpretation utilizing WSR-88 Doppler technology is a WSR-88D interrogation of Tropical Storm Ed's 1993 essential. This can be achieved by further de®ning the landfall on Guam. While these inner rainband vorticies structure and evolution of TC±tornadoes through mod- can be signi®cant to the local warning meteorologist el simulation efforts (e.g., McCaul 1990; Weisman and (Fujita 1993; Wakimoto and Black 1994), this paper McCaul 1995) and through case study analyses (e.g., will strictly focus upon outer rainband mesocyclones McCaul 1987; Snell and McCaul 1993; Zubrick and and associated tornadoes, as observed during TC's Belville 1993; Cammarata et al. 1996). Speci®c to out- Gordon and Allison. er band tornadogenesis, McCaul (1987), McCaul et al. The occurrence of multiple tornadoes, or tornado (1993), and Snell and McCaul (1993) have made sig- outbreaks, associated with tropical cyclones has been ni®cant contributions via the analysis of data from sev- a problem facing operational meteorologists for some eral 10-cm/WSR-57 radars and a Doppler-enhanced time. Multiple tornadoes are often observed to be as- 5-cm/WSR-74C radar during the postlandfall tornado sociated with the strongest convective cells within the outbreaks associated with Hurricane's Danny (1985) outer rainbands (Hill et al. 1966; Fujita et al. 1972), and Andrew (1992). The present paper will build upon where convergence and vorticity gradients are the the foundation established by the previously sited au- greatest. Several studies (Novlan and Gray 1974; Gen- thors. try 1983; Weiss 1985) have described characteristics Radar signatures of multiple tornadic mesocyclones of the tropical cyclone environment that have occa- associated with banded convection of Tropical Storm sionally become conducive for the occurrence of mul- Gordon (1994) and Hurricane Allison (1995) will be tiple tornado events. McCaul (1991) analyzed 1296 investigated using products from three Florida 10-cm/ rawinsonde observations (raobs) that were within 3 h WSR-88Ds. During each event, outer band convection and 200 km of an observed TC-tornado and computed resulted in an ``outbreak'' of tornadoes as de®ned by the spatial distribution of potential buoyant energy (or Hagemeyer and Hodanish (1995), within a highly convective available potential energy, CAPE) and 0± sheared and weakly buoyant environment. The major- 3-km storm-relative helicity (SRH), which provides an ity of these tornadoes occurred very near the coast and estimate of a cell's potential of developing a rotating were weak (F0±F1) with short tracks; however, a brief updraft. Results showed the SRH was maximized to F2 tornado did produce numerous casualties and con- the right of the cyclone with increasing CAPE at great- siderable destruction. er distances. Restricting raobs to those within 2 h and Section 2 will provide a background of some sam- 40 km of hurricane-spawned tornadoes and made on pling considerations of the WSR-88D related to the the outer side of any rainbands in which the tornadoes observation of tropical, low-topped rotational cells. were embedded, McCaul produced a composite of 10 Sections 3 through 6 will present short synoptic over- soundings with a buoyancy (CAPE) of only 253 J kg21 views and storm-scale discussions of each tornado and an approximate SRH of 300 m2 s22. In a compar- event by examining the temporal trends of several ra- ison with nontropical tornado
Load more

Recommended publications
  • A Study of Synoptic-Scale Tornado Regimes
    Garner, J. M., 2013: A study of synoptic-scale tornado regimes. Electronic J. Severe Storms Meteor., 8 (3), 1–25. A Study of Synoptic-Scale Tornado Regimes JONATHAN M. GARNER NOAA/NWS/Storm Prediction Center, Norman, OK (Submitted 21 November 2012; in final form 06 August 2013) ABSTRACT The significant tornado parameter (STP) has been used by severe-thunderstorm forecasters since 2003 to identify environments favoring development of strong to violent tornadoes. The STP and its individual components of mixed-layer (ML) CAPE, 0–6-km bulk wind difference (BWD), 0–1-km storm-relative helicity (SRH), and ML lifted condensation level (LCL) have been calculated here using archived surface objective analysis data, and then examined during the period 2003−2010 over the central and eastern United States. These components then were compared and contrasted in order to distinguish between environmental characteristics analyzed for three different synoptic-cyclone regimes that produced significantly tornadic supercells: cold fronts, warm fronts, and drylines. Results show that MLCAPE contributes strongly to the dryline significant-tornado environment, while it was less pronounced in cold- frontal significant-tornado regimes. The 0–6-km BWD was found to contribute equally to all three significant tornado regimes, while 0–1-km SRH more strongly contributed to the cold-frontal significant- tornado environment than for the warm-frontal and dryline regimes. –––––––––––––––––––––––– 1. Background and motivation As detailed in Hobbs et al. (1996), synoptic- scale cyclones that foster tornado development Parameter-based and pattern-recognition evolve with time as they emerge over the central forecast techniques have been essential and eastern contiguous United States (hereafter, components of anticipating tornadoes in the CONUS).
    [Show full text]
  • Hurricane Outer Rainband Mesovortices
    Presented at the 24th Conference on Hurricanes and Tropical Meteorology, Ft. Lauderdale, FL, May 31 2000 EXAMINING THE PRE-LANDFALL ENVIRONMENT OF MESOVORTICES WITHIN A HURRICANE BONNIE (1998) OUTER RAINBAND 1 2 2 1 Scott M. Spratt , Frank D. Marks , Peter P. Dodge , and David W. Sharp 1 NOAA/National Weather Service Forecast Office, Melbourne, FL 2 NOAA/AOML Hurricane Research Division, Miami, FL 1. INTRODUCTION Tropical Cyclone (TC) tornado environments have been studied for many decades through composite analyses of proximity soundings (e.g. Novlan and Gray 1974; McCaul 1986). More recently, airborne and ground-based Doppler radar investigations of TC rainband-embedded mesocyclones have advanced the understanding of tornadic cell lifecycles (Black and Marks 1991; Spratt et al. 1997). This paper will document the first known dropwindsonde deployments immediately adjacent to a family of TC outer rainband mesocyclones, and will examine the thermodynamic and wind profiles retrieved from the marine environment. A companion paper (Dodge et al. 2000) discusses dual-Doppler analyses of these mesovortices. On 26 August 1998, TC Bonnie made landfall as a category two hurricane along the North Carolina coast. Prior to landfall, two National Oceanographic and Atmospheric Administration (NOAA) Hurricane Research Division (HRD) aircraft conducted surveillance missions offshore the Carolina coast. While performing these missions near altitudes of 3.5 and 2.1 km, both aircraft were required to deviate around intense cells within a dominant outer rainband, 165 to 195 km northeast of the TC center. On-board radars detected apparent mini-supercell signatures associated with several of the convective cells along the band.
    [Show full text]
  • Subtropical Storms in the South Atlantic Basin and Their Correlation with Australian East-Coast Cyclones
    2B.5 SUBTROPICAL STORMS IN THE SOUTH ATLANTIC BASIN AND THEIR CORRELATION WITH AUSTRALIAN EAST-COAST CYCLONES Aviva J. Braun* The Pennsylvania State University, University Park, Pennsylvania 1. INTRODUCTION With the exception of warmer SST in the Tasman Sea region (0°−60°S, 25°E−170°W), the climate associated with South Atlantic ST In March 2004, a subtropical storm formed off is very similar to that associated with the coast of Brazil leading to the formation of Australian east-coast cyclones (ECC). A Hurricane Catarina. This was the first coastal mountain range lies along the east documented hurricane to ever occur in the coast of each continent: the Great Dividing South Atlantic basin. It is also the storm that Range in Australia (Fig. 1) and the Serra da has made us reconsider why tropical storms Mantiqueira in the Brazilian Highlands (Fig. 2). (TS) have never been observed in this basin The East Australia Current transports warm, although they regularly form in every other tropical water poleward in the Tasman Sea tropical ocean basin. In fact, every other basin predominantly through transient warm eddies in the world regularly sees tropical storms (Holland et al. 1987), providing a zonal except the South Atlantic. So why is the South temperature gradient important to creating a Atlantic so different? The latitudes in which TS baroclinic environment essential for ST would normally form is subject to 850-200 hPa formation. climatological shears that are far too strong for pure tropical storms (Pezza and Simmonds 2. METHODOLOGY 2006). However, subtropical storms (ST), as defined by Guishard (2006), can form in such a.
    [Show full text]
  • The Influences of the North Atlantic Subtropical High and the African Easterly Jet on Hurricane Tracks During Strong and Weak Seasons
    Meteorology Senior Theses Undergraduate Theses and Capstone Projects 2018 The nflueI nces of the North Atlantic Subtropical High and the African Easterly Jet on Hurricane Tracks During Strong and Weak Seasons Hannah Messier Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/mteor_stheses Part of the Meteorology Commons Recommended Citation Messier, Hannah, "The nflueI nces of the North Atlantic Subtropical High and the African Easterly Jet on Hurricane Tracks During Strong and Weak Seasons" (2018). Meteorology Senior Theses. 40. https://lib.dr.iastate.edu/mteor_stheses/40 This Dissertation/Thesis is brought to you for free and open access by the Undergraduate Theses and Capstone Projects at Iowa State University Digital Repository. It has been accepted for inclusion in Meteorology Senior Theses by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. The Influences of the North Atlantic Subtropical High and the African Easterly Jet on Hurricane Tracks During Strong and Weak Seasons Hannah Messier Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa Alex Gonzalez — Mentor Department of Geological and Atmospheric Sciences, Iowa State University, Ames Iowa Joshua J. Alland — Mentor Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, New York ABSTRACT The summertime behavior of the North Atlantic Subtropical High (NASH), African Easterly Jet (AEJ), and the Saharan Air Layer (SAL) can provide clues about key physical aspects of a particular hurricane season. More accurate tropical weather forecasts are imperative to those living in coastal areas around the United States to prevent loss of life and property.
    [Show full text]
  • Lecture 15 Hurricane Structure
    MET 200 Lecture 15 Hurricanes Last Lecture: Atmospheric Optics Structure and Climatology The amazing variety of optical phenomena observed in the atmosphere can be explained by four physical mechanisms. • What is the structure or anatomy of a hurricane? • How to build a hurricane? - hurricane energy • Hurricane climatology - when and where Hurricane Katrina • Scattering • Reflection • Refraction • Diffraction 1 2 Colorado Flood Damage Hurricanes: Useful Websites http://www.wunderground.com/hurricane/ http://www.nrlmry.navy.mil/tc_pages/tc_home.html http://tropic.ssec.wisc.edu http://www.nhc.noaa.gov Hurricane Alberto Hurricanes are much broader than they are tall. 3 4 Hurricane Raymond Hurricane Raymond 5 6 Hurricane Raymond Hurricane Raymond 7 8 Hurricane Raymond: wind shear Typhoon Francisco 9 10 Typhoon Francisco Typhoon Francisco 11 12 Typhoon Francisco Typhoon Francisco 13 14 Typhoon Lekima Typhoon Lekima 15 16 Typhoon Lekima Hurricane Priscilla 17 18 Hurricane Priscilla Hurricanes are Tropical Cyclones Hurricanes are a member of a family of cyclones called Tropical Cyclones. West of the dateline these storms are called Typhoons. In India and Australia they are called simply Cyclones. 19 20 Hurricane Isaac: August 2012 Characteristics of Tropical Cyclones • Low pressure systems that don’t have fronts • Cyclonic winds (counter clockwise in Northern Hemisphere) • Anticyclonic outflow (clockwise in NH) at upper levels • Warm at their center or core • Wind speeds decrease with height • Symmetric structure about clear "eye" • Latent heat from condensation in clouds primary energy source • Form over warm tropical and subtropical oceans NASA VIIRS Day-Night Band 21 22 • Differences between hurricanes and midlatitude storms: Differences between hurricanes and midlatitude storms: – energy source (latent heat vs temperature gradients) - Winter storms have cold and warm fronts (asymmetric).
    [Show full text]
  • The Lagrange Torando During Vortex2. Part Ii: Photogrammetry Analysis of the Tornado Combined with Dual-Doppler Radar Data
    6.3 THE LAGRANGE TORANDO DURING VORTEX2. PART II: PHOTOGRAMMETRY ANALYSIS OF THE TORNADO COMBINED WITH DUAL-DOPPLER RADAR DATA Nolan T. Atkins*, Roger M. Wakimoto#, Anthony McGee*, Rachel Ducharme*, and Joshua Wurman+ *Lyndon State College #National Center for Atmospheric Research +Center for Severe Weather Research Lyndonville, VT 05851 Boulder, CO 80305 Boulder, CO 80305 1. INTRODUCTION studies, however, that have related the velocity and reflectivity features observed in the radar data to Over the years, mobile ground-based and air- the visual characteristics of the condensation fun- borne Doppler radars have collected high-resolu- nel, debris cloud, and attendant surface damage tion data within the hook region of supercell (e.g., Bluestein et al. 1993, 1197, 204, 2007a&b; thunderstorms (e.g., Bluestein et al. 1993, 1997, Wakimoto et al. 2003; Rasmussen and Straka 2004, 2007a&b; Wurman and Gill 2000; Alexander 2007). and Wurman 2005; Wurman et al. 2007b&c). This paper is the second in a series that pre- These studies have revealed details of the low- sents analyses of a tornado that formed near level winds in and around tornadoes along with LaGrange, WY on 5 June 2009 during the Verifica- radar reflectivity features such as weak echo holes tion on the Origins of Rotation in Tornadoes Exper- and multiple high-reflectivity rings. There are few iment (VORTEX 2). VORTEX 2 (Wurman et al. 5 June, 2009 KCYS 88D 2002 UTC 2102 UTC 2202 UTC dBZ - 0.5° 100 Chugwater 100 50 75 Chugwater 75 330° 25 Goshen Co. 25 km 300° 50 Goshen Co. 25 60° KCYS 30° 30° 50 80 270° 10 25 40 55 dBZ 70 -45 -30 -15 0 15 30 45 ms-1 Fig.
    [Show full text]
  • Meteorology – Lecture 19
    Meteorology – Lecture 19 Robert Fovell [email protected] 1 Important notes • These slides show some figures and videos prepared by Robert G. Fovell (RGF) for his “Meteorology” course, published by The Great Courses (TGC). Unless otherwise identified, they were created by RGF. • In some cases, the figures employed in the course video are different from what I present here, but these were the figures I provided to TGC at the time the course was taped. • These figures are intended to supplement the videos, in order to facilitate understanding of the concepts discussed in the course. These slide shows cannot, and are not intended to, replace the course itself and are not expected to be understandable in isolation. • Accordingly, these presentations do not represent a summary of each lecture, and neither do they contain each lecture’s full content. 2 Animations linked in the PowerPoint version of these slides may also be found here: http://people.atmos.ucla.edu/fovell/meteo/ 3 Mesoscale convective systems (MCSs) and drylines 4 This map shows a dryline that formed in Texas during April 2000. The dryline is indicated by unfilled half-circles in orange, pointing at the more moist air. We see little T contrast but very large TD change. Dew points drop from 68F to 29F -- huge decrease in humidity 5 Animation 6 Supercell thunderstorms 7 The secret ingredient for supercells is large amounts of vertical wind shear. CAPE is necessary but sufficient shear is essential. It is shear that makes the difference between an ordinary multicellular thunderstorm and the rotating supercell. The shear implies rotation.
    [Show full text]
  • Tornadogenesis in a Simulated Mesovortex Within a Mesoscale Convective System
    3372 JOURNAL OF THE ATMOSPHERIC SCIENCES VOLUME 69 Tornadogenesis in a Simulated Mesovortex within a Mesoscale Convective System ALEXANDER D. SCHENKMAN,MING XUE, AND ALAN SHAPIRO Center for Analysis and Prediction of Storms, and School of Meteorology, University of Oklahoma, Norman, Oklahoma (Manuscript received 3 February 2012, in final form 23 April 2012) ABSTRACT The Advanced Regional Prediction System (ARPS) is used to simulate a tornadic mesovortex with the aim of understanding the associated tornadogenesis processes. The mesovortex was one of two tornadic meso- vortices spawned by a mesoscale convective system (MCS) that traversed southwestern and central Okla- homa on 8–9 May 2007. The simulation used 100-m horizontal grid spacing, and is nested within two outer grids with 400-m and 2-km grid spacing, respectively. Both outer grids assimilate radar, upper-air, and surface observations via 5-min three-dimensional variational data assimilation (3DVAR) cycles. The 100-m grid is initialized from a 40-min forecast on the 400-m grid. Results from the 100-m simulation provide a detailed picture of the development of a mesovortex that produces a submesovortex-scale tornado-like vortex (TLV). Closer examination of the genesis of the TLV suggests that a strong low-level updraft is critical in converging and amplifying vertical vorticity associated with the mesovortex. Vertical cross sections and backward trajectory analyses from this low-level updraft reveal that the updraft is the upward branch of a strong rotor that forms just northwest of the simulated TLV. The horizontal vorticity in this rotor originates in the near-surface inflow and is caused by surface friction.
    [Show full text]
  • ANNUAL SUMMARY Atlantic Hurricane Season of 2005
    MARCH 2008 ANNUAL SUMMARY 1109 ANNUAL SUMMARY Atlantic Hurricane Season of 2005 JOHN L. BEVEN II, LIXION A. AVILA,ERIC S. BLAKE,DANIEL P. BROWN,JAMES L. FRANKLIN, RICHARD D. KNABB,RICHARD J. PASCH,JAMIE R. RHOME, AND STACY R. STEWART Tropical Prediction Center, NOAA/NWS/National Hurricane Center, Miami, Florida (Manuscript received 2 November 2006, in final form 30 April 2007) ABSTRACT The 2005 Atlantic hurricane season was the most active of record. Twenty-eight storms occurred, includ- ing 27 tropical storms and one subtropical storm. Fifteen of the storms became hurricanes, and seven of these became major hurricanes. Additionally, there were two tropical depressions and one subtropical depression. Numerous records for single-season activity were set, including most storms, most hurricanes, and highest accumulated cyclone energy index. Five hurricanes and two tropical storms made landfall in the United States, including four major hurricanes. Eight other cyclones made landfall elsewhere in the basin, and five systems that did not make landfall nonetheless impacted land areas. The 2005 storms directly caused nearly 1700 deaths. This includes approximately 1500 in the United States from Hurricane Katrina— the deadliest U.S. hurricane since 1928. The storms also caused well over $100 billion in damages in the United States alone, making 2005 the costliest hurricane season of record. 1. Introduction intervals for all tropical and subtropical cyclones with intensities of 34 kt or greater; Bell et al. 2000), the 2005 By almost all standards of measure, the 2005 Atlantic season had a record value of about 256% of the long- hurricane season was the most active of record.
    [Show full text]
  • A Long-Lasting Vortex Rossby Wave–Induced Rainband of Typhoon Longwang (2005)
    A Long-Lasting Vortex Rossby Wave–Induced Rainband of Typhoon Longwang (2005) YANLUAN LIN, YUANLONG LI, QINGSHAN LI, MINYAN CHEN, FANGHUA XU, YUQING WANG, AND BIN HUANG n 2 October 2005, a record-breaking rainfall event Tsai 2013). As Typhoon Longwang approached the with 152 mm of rainfall in an hour occurred as coast of Fujian Province at 0800 UTC, one type of this OTyphoon Longwang approached Fujian Province, transient rainband in the northeast sector started to China. The severe rainfall was unexpected and signifi- weaken and dissipate (Fig. 1b). At the same time, the cantly underpredicted by the local weather forecasters eyewall underwent an asymmetry transformation and caused a total of 96 deaths. Because of the severe accompanied by a bended convection pattern in the damage over Taiwan and mainland China, the name north (Fig. 1b). The bended convection transformed of Longwang, which means a dragon in charge of into a strong convective band along the eyewall to the rainfall in Chinese, was removed from the name list north and moved outward relative to the storm center for future typhoons. (Fig. 1c). The convective band continued to intensify with a sharp inner edge (Fig. 1d). An hour later, the EVOLUTION AND BASIC FEATURES OF convective band achieved its maximum intensity with THE RAINBAND. The formation and evolution a large area of stratiform precipitation outward and of the rainband associated with the rainfall event was downstream (Fig. 1e). At this time, cloud brightness captured by the radar mosaic produced by the Central temperatures as low as −80°C were measured by a Weather Bureau (CWB) of Taiwan (Fig.
    [Show full text]
  • Hurricane & Tornado Risks in June
    June 4, 2021 Hurricane & Tornado Risks in June · Several changes in the weather typically occur in June across the Lower 48. Tropical Development · Atlantic hurricane season officially starts June 1, although it has started early the last seven years, including this year. · On average in the Atlantic Basic, one named storm forms every one to two years in June and a hurricane develops about once every five years. · Early in the season, tropical systems tend to form close to the U.S. and often affect the Southeastern U.S., the western Caribbean and parts of Central America. Rainfall, rather than wind, is usually the biggest concern with June tropical cyclones. Tornado Risks · June is typically an active month for tornadoes. · Tornadoes can happen just about anywhere in the Lower 48 in June, given the widespread warmth and humidity. · Low pressure systems can create the ingredients for severe weather in the Plains and Midwest, in particular. The area at greatest risk of tornadoes in June stretches from central Oklahoma into southwestern Minnesota. · Brief, usually weaker tornadoes often occur near the Gulf Coast during the summer. These are usually caused by sea-breeze thunderstorms and sea breeze collisions closer to the coast. Scattered thunderstorms can also create brief tornadoes across much of the South. · Tropical systems can also bring tornadoes, although they are usually weak and short-lived. · Peak hail activity also occurs in June, according to some studies. The Central and Southern Plains see an increase in hail during the early summer due to the combination of the jet stream, moisture from the Gulf of Mexico and daytime heating.
    [Show full text]
  • Quasi-Linear Convective System Mesovorticies and Tornadoes
    Quasi-Linear Convective System Mesovorticies and Tornadoes RYAN ALLISS & MATT HOFFMAN Meteorology Program, Iowa State University, Ames ABSTRACT Quasi-linear convective system are a common occurance in the spring and summer months and with them come the risk of them producing mesovorticies. These mesovorticies are small and compact and can cause isolated and concentrated areas of damage from high winds and in some cases can produce weak tornadoes. This paper analyzes how and when QLCSs and mesovorticies develop, how to identify a mesovortex using various tools from radar, and finally a look at how common is it for a QLCS to put spawn a tornado across the United States. 1. Introduction Quasi-linear convective systems, or squall lines, are a line of thunderstorms that are Supercells have always been most feared oriented linearly. Sometimes, these lines of when it has come to tornadoes and as they intense thunderstorms can feature a bowed out should be. However, quasi-linear convective systems can also cause tornadoes. Squall lines and bow echoes are also known to cause tornadoes as well as other forms of severe weather such as high winds, hail, and microbursts. These are powerful systems that can travel for hours and hundreds of miles, but the worst part is tornadoes in QLCSs are hard to forecast and can be highly dangerous for the public. Often times the supercells within the QLCS cause tornadoes to become rain wrapped, which are tornadoes that are surrounded by rain making them hard to see with the naked eye. This is why understanding QLCSs and how they can produce mesovortices that are capable of producing tornadoes is essential to forecasting these tornadic events that can be highly dangerous.
    [Show full text]