ANALYSIS OF TORNADO CHARACTERISTICS IN THE STATE OF SÃO PAULO FOR THE IMPROVEMENT OF AN AUTOMATIC ALERT SYSTEM

Sep 8, 2026

Severe storms in São Paulo, Brazil, repeatedly produce strong winds, hail, intense lightning, and flash floods, causing extensive agricultural and urban damage as well as fatalities. Prior studies focused on identifying radar and lightning signatures usable for storm severity indicators and for automated alert algorithms. Tornado occurrence during May 2004–2005, observed by Bauru and Presidente Prudente S-band Doppler radars, motivates a detailed investigation. The study links synoptic conditions, radar reflectivity and velocities, and lightning observations to improve nowcasting and early warning for SIHESP.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages10

Reading Time25 min

AccessFree to download

Introduction

Synoptic Situations

25 May 2004

24 May 2005

ANALYSIS OF TORNADO CHARACTERISTICS IN THE STATE OF SÃO PAULO FOR THE IMPROVEMENT OF AN AUTOMATIC ALERT SYSTEM P3R.9 Gerhard Held1*, Ana Maria Gomes1 , Kleber P. Naccarato2 , Osmar Pinto Jr.2 , Ernani de Lima Nascimento3 , Adelmo Antonio Correia1 and Isabela P.V.O. Marcelino4 1 Instituto de Pesquisas Meteorológicas, Universidade Estadual Paulista, Bauru, S. P. , Brazil 2 Grupo de3IEnsletittruictaTe AcnotlmoógiscrSicIa,MEInPstAituR, toUie Peversiqaisase FeEspderaalcdiaoisP, SaronJá,osCdritoisbaC, amPRpos , S.P. 4 Instituto de Geociências, Universidade Estadual de Campinas , Campinas , S. P. 1. INTRODUCTION The structures of severe storms in the State of São Paulo, Brazil, which cause enormous damage to agriculture, urban areas, industries , as well as loss of many lives, due to strong winds, hailstones, intense lightning and flash floods, have been studied for many years (Gomes et al. , 2000, Held et al. , 2001; Held and Gomes, 2003) . Efforts had been concentrated on identifying specific signatures during severe storm events, which could be used by the forecaster as indicators of storm severity, as well as to develop algorithms for an automated alert system. Until recently, it was believed, that tornadoes were rather rare events in Brazil, and very few of those reported had been observed within radar range (Gomes et al. , 2000) . However, two tornadoes occurred during the afternoon of 25 May 2004 in the west of the State of São Paulo (Held et al. , 2004, 2005), and their tornado-vortex signatures had been observed by the S-band Doppler radars located in Bauru and Presidente Prudente, respectively (Figure 1) . Another significant tornadic storm was recorded by the Bauru radar on 24 May 2005. These well-documented occurrences prompted a detailed investigation, inan attempt to find relevant signatures in radar and lightning observations , which could be used for nowcasting and an early alert system. This is vitally important for the SIHESP (Portuguese acronym for “Hydro-meteorological System of the State of São Paulo”) Project, which is currently being implemented, to provide early warnings of severe storms to local authorities, Civil Defense Organizations, industry and the general public. The radars are located in Bauru (Lat: 22°21’28” S, Lon: 49°01’36” W, 624 m amsl) and in Presidente Prudente, 240 km west of Bauru (Lat: * Corresponding author address: Gerhard Held, Instituto de Pesquisas Meteorológicas, UNESP, CX-281, 17001-970 Bauru, S. P. , Brazil; e-mail: [gerhard@ipmet.unesp.br](gerhard@ipmet.unesp.br) 22°10’30” S, Lon: 51°22’22” W, 460 m amsl) . Both have a 2° beam width and a range of 450 km for surveillance, but when operated in volume-scan mode every 7.5 minutes it is limited to 240 km, with a resolution of 1 km radially and 1° in azimuth, recording reflectivities and radial velocities. The reflectivity threshold for this study was set at 10 dBZ. Both radars have Sigmet processors and run under the IRIS Operating System. Figure 1. IPMet’s Radar Network (BRU = Bauru; PPR = Presidente Prudente), showing 240 and 450 km range rings. The areas where the tornadoes occurred are marked T1 (Palmital), T2 (Lençois) and T3 (Indaiatuba) . 2. SYNOPTIC SITUATIONS The synoptic situation on 25 May 2004 was dominated by an extra-tropical cyclone over the South Atlantic Ocean, off the coast of Southeast Brazil, from which a cold front extended far into the interior, sweeping across the western part of the State of São Paulo (Figure 2) . The frontal movement was accompanied by relatively strong convective activity in the western part of the State during the morning (Figure 4), due to a strong lowlevel convergence, overlaid by divergence above 500 hPa, which created very unstable conditions (Held et al. , 2004) . While traversing the farming Figure 2. Extract from EUMETSAT-7 picture (visible) on 25 May 2004, 16:00UT (13:00 Local Time; LT=UT-3h) . (Source: CPTEC/INPE) . region of Palmital, one of the s

FAQs

Why is an automatic alert system important for tornadoes in São Paulo?

The document states that an improved alert system is vital for the SIHESP project to provide early warnings of severe storms to authorities, civil defense organizations, industry, and the public.

What radar data are used in the tornado analysis?

The study uses S-band Doppler radars in Bauru and Presidente Prudente, recording reflectivities and radial velocities, with a reflectivity threshold set at 10 dBZ.

Which weather patterns are associated with the tornado outbreaks discussed?

On 25 May 2004, an extra-tropical cyclone and a cold front produced unstable conditions via low-level convergence and divergence above 500 hPa. On 24 May 2005, a baroclinic system with a rapidly moving cold front and strong divergence at 200 hPa led to widespread instability and a tornadic cell.

Sep 8, 2026

Upload by Pentious