20 By Franklyn Michael Supplementary Associate, CARICAD O ne of my most persistent memories of my days in the Disaster Management orbit is that of friends, colleagues and acquaintances at the start of each hurricane season asking me pointedly – “What’s the forecast for this year?”. They were unquestionably referring to the forecast of Atlantic hurricane activity that had been forecast by Colorado State University (CSU). Those memories have stayed with me. What has also stayed is the significance that our people continue to attach to that forecast. My perception was reinforced on June 1st of this year, (the official start of the hurricane season) when I heard just how many public officials who made remarks to bring attention to the season made reference to the forecast. I became convinced that in this 2023 edition of our Horizon Newsletter, CARICAD needs to say more about the forecast for the season. The late Dr. William (Bill) Gray formerly of Colorado State University (CSU) is widely recognised as the early pioneer of Atlantic Hurricane season forecasting. He issued the first such forecast in 1984. He continued for 30 years thereafter. He led the CSU hurricane research programme for many years. He died in 2016 at the age of 86. He had retired in 2005 but remained involved in atmospheric science as a professor emeritus until his passing. Dr. Gray had found that there was clear scientific evidence of associations between the level of hurricane activity and specific climate patterns. We must remember that climate is regarded as weather in the long-term. Dr. Gray had realised that when the weather pattern that is known as El Niño was in place, there was less hurricane activity in the Atlantic basin. He realised that El Niño affected the high levels winds that could cause wind shear of weather systems in the Atlantic. NOAA explains El Niño as: SOURCE: National Hurricane Center A naturally occurring climate pattern associated with warming of the ocean surface temperatures in the central and eastern tropical Pacific Ocean, which can significantly influence weather patterns, ocean conditions, and marine fisheries worldwide. El Niño occurs on average every two to seven years, and episodes typically last nine to 12 months. El Niño has its largest impacts during the winter. In the winter, El Niño typically brings milder weather to the northern parts of the United States and wetter conditions across the southern United States. The opposite of El Niño is La Niña, the cold phase, which also changes weather worldwide. There is also a neutral stage with neither unusually warm nor cool water in the equatorial Pacific. All three stages together are referred to as ENSO or the El Niño-Southern Oscillation. In the U.S., NOAA declares when an El Niño or La Niña event has begun. For El Niño conditions to form, monthly sea surface temperatures in the central and eastern tropical Pacific Ocean (Nino 3.4 region) need to warm +0.5° Celsius above normal, with the expectation that the warming will persist for five consecutive overlapping three-month periods. In addition, the atmosphere must respond to the warming water by weakening the prevailing winds, known as the tradewinds and also shift patterns of tropical rainfall eastward. This ocean–atmosphere coupling impacts the position of • Continues on next page
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