212 | WMO Bulletin 56 (3) - July 2007 Title Introduction In the heart of every meteorologist and climatologist beats the soul of a detective. We all appreciate a good mystery and, for those interested in weather, the elements of our atmosphere can often provide the most fascinating puzzles. In particular, can we determine, after a major weather or climate event has occurred, whether that event actually was a world weather record? Was it the hottest, the coldest, the wettest or the windiest? Puzzles of this type are now being actively investigated by members of special ad hoc world record weather extremes committees of WMO’s Commission for Climatology (CCl). These committees are created on an “as-needed” basis to assess the occurrence of specific potential world, hemispheric and regional weather extreme records, such as maximum and minimum temperatures, highest and lowest pressures and various rainfall amounts. Many people ask what were the hottest, coldest, wettest, driest observations ever recorded and, interestingly, several different self- appointed experts have responded to these questions. Their answers, however, do not necessarily agree. As these records amount to coveted “bragging rights” and are critical to monitoring and evaluating climate change, the Commission for Climatology decided to appoint a Rapporteur on Climate Extremes to keep an official, unbiased list ( http://www.wmo.int/web/wcp/ ccl/opags/opag2/ET/R2.3_ToRs. htm). When a new record has been reported, the Rapporteur organizes an ad hoc extremes committee to provide an expert and unbiased recommendation as to whether the extreme in question should be added to the list. The committee consists of the president of the Commission for Climatology, the Chair of the CCl Open Programme Area Group (OPAG) on Monitoring and Analysis of Climate Variability and Change (the Rapporteur is part of this OPAG) and a representative of the relevant Member State’s National Meteorological or Hydrometeorological Service, as well as experts in the appropriate meteorological phenomenon and observing instrumentation as required. The committee may also consult with a wide variety of additional experts. A new western hemisphere 24-hour rainfall record by Randall Cerveny 1 , Valentina Davydova Belitskaya 2 , Pierre Bessemoulin 3 , Miguel Cortez 4 , Chris Landsea 5 and Thomas C. Peterson 6 1 Arizona State University, USA 2 National Meteorological Service, Mexico 3 Météo-France 4 National University of Mexico, Mexico (deceased) 5 National Hurricane Center, National Oceanographic and Atmospheric Administration (NOAA), USA 6 National Climatic Data Center, NOAA, USA Ground view of the Isla Mujeres station