News
03/28/2024, 12:04 pm EDT

Tropical Feature: North Atlantic 2024 Tropical Cyclone Season Forecast Summary

Executive summary: The Climate Impact Company (CIC) 2024 North Atlantic basin tropical cyclone (TC) season forecast projects 20 tropical storms, 10 hurricanes, and 5 intense hurricanes. The accumulative cyclone energy (ACE) index forecast is 187. The activity forecast is somewhat higher than normal. The forecast is based on strongly favorable environmental conditions including a low shear upper-level environment due to the evolution of La Nina and plentiful upper ocean heat in the deep tropics and subtropics as identified by the tropical North Atlantic (TNA) index. The projected hurricane tracks for the 2024 season based on the CIC constructed analog and climatology is dangerous featuring potential for 5 land-falling systems. Forecasts issued by Colorado State University on April 4 and Tropical Storm Risk/U.K. on April 8 are likely as active or slightly more active than the CIC projection. An extremely dangerous TC season ahead is expected. Fig. 1: The Climate Impact Company seasonal activity forecast and projected hurricane tracks for the 2024 North Atlantic basin TC season. The analog forecast: The Climate Impact Company constructed-analog (CIC-CA) forecast of North Atlantic basin tropical cyclone activity is based on ENSO and TNA years similar with projections for the 2024 season. Fortunately, the selected years are very straightforward and include 2016, 2010, 1998, and 1995. Each analog year produced an El Nino to La Nina transition with strong warm sea surface temperature anomalies (SSTA) in the North Atlantic tropics similar with the 2024 expectations. The correction bias is based on 1999-2023 CIC April forecasts and verification error bias (Fig. 2) which is +2.58 for tropical storms, +0.375 for both hurricanes and intense hurricanes, and +8.1 for ACE index. The bias values are positive due to the warming of the North Atlantic causing a tendency for seasonal forecasts to underperform (slightly). The bias is added to the constructed analog values to create the final forecast (Table 1). Fig. 2: The Climate Impact Company April seasonal forecasts for North Atlantic tropical cyclone activity and observations for 1999-2023. Tropical Storms Hurricanes Intense Hurricanes ACE Index 2016 15 7 4 141 2010 19 12 5 166 1998 14 10 3 182 1995 19 11 5 227 Average 17.0 10.0 4.25 179.0 Correction +2.58 +0.375 +0.375 +8.1 Forecast 20 10 5 187 Last Year 20 7 3 146 30-Year NML 130.4 15.5 7.5 3.4 15-Year NML 132.5 17.7 7.9 3.5 50-Year NML 107.0 13.0 6.6 2.7 Table 1: The CIC-CA North Atlantic basin 2024 seasonal tropical cyclone activity forecast.  
03/27/2024, 10:00 am EDT

Tropical Feature: Reworking North Atlantic basin seasonal tropical cyclone climatology based on ENSO and tropical North Atlantic index.

Fig. 1: Renewed seasonal North Atlantic tropical cyclone climatology for 1950-2023 based on ENSO phase using AUG/SEP/OCT operational Nino index (ONI). Climate Impact Company has renewed seasonal North Atlantic tropical cyclone climatology for 1950-2023 for both El Nino southern oscillation (ENSO) and tropical North Atlantic (TNA) index phase and intensity. The climatology is based on ENSO and TNA index for AUG/SEP/OCT of each year. The ENSO climatology reveals that the most active seasonal activity occurs with moderate La Nina episodes while least active hurricane years are associated with strong El Nino (Fig. 1). In 2024, ENSO is projected to transition from weak to moderate intensity La Nina during AUG/SEP/OCT. TNA index is convenient due to its measurement in the main development region (MDR) for North Atlantic hurricanes located between the eastern edge of the Caribbean Sea and waters off Northwest Africa. Not surprisingly, the strong positive (warm) TNA regime yields the most active tropical cyclone seasons while moderately cool TNA is associated with the least active seasonal activity (Fig. 2). In 2024, record +TNA is likely to continue. During the shift to the warm cycle of the Atlantic multi-decadal oscillation (+AMO) in the late 1990’s, +TNA during AUG/SEP/OCT has occurred each year except 2007, 2002, and 2000. Since 2008, moderate to strong +TNA has occurred in every year except 2018. In 2024, strong +TNA occurs for the 4th time in the past 5 years. Three of the 4 years on record when 20 (or more) tropical cyclones have occurred in one season are from 3 of the past 4 seasons. Given the shift toward moderate La Nina late this year combined with the ongoing record +TNA, more than 20 tropical cyclones for the 2024 season is VERY likely. Fig. 2: Renewed seasonal North Atlantic tropical cyclone climatology for 1950-2023 based on tropical North Atlantic (TNA) index.