A Hyperactive End to the Atlantic Hurricane Season: October–November 2020

The active 2020 Atlantic hurricane season produced 30 named storms, 14 hurricanes, and 7 major hurricanes (Category 3+ on the Saffir-Simpson Hurricane Wind Scale). Though the season was active overall, the final two months (October–November) raised 2020 into the upper echelon of Atlantic hurricane activity for integrated metrics such as Accumulated Cyclone Energy (ACE). This study focuses on October–November 2020, when 7 named storms, 6 hurricanes, and 5 major hurricanes formed and produced ACE of 74 * 104 kt2. Since 1950, October–November 2020 ranks tied for 3rd for named storms, 1st for hurricanes and major hurricanes, and 2nd for ACE. Six named storms also underwent rapid intensification (≥30 kt intensification in ≤24 hr) in October–November 2020—the most on record.This manuscript includes a climatological analysis of October–November tropical cyclones (TCs) and their primary formation regions. In 2020, anomalously low wind shear in the western Caribbean and Gulf of Mexico, likely driven by a moderate intensity La Niña event and anomalously high sea surface temperatures (SSTs) in the Caribbean provided dynamic and thermodynamic conditions that were much more conducive than normal for late-season TC formation and rapid intensification. This study also highlights October–November 2020 landfalls, including Hurricanes Delta and Zeta in Louisiana and in Mexico and Hurricanes Eta and Iota in Nicaragua. The active late season in the Caribbean would have been anticipated by a statistical model using the July–September-averaged ENSO Longitude Index and Atlantic warm pool SSTs as predictors.

Changes in Atlantic major hurricane frequency since the late-19th century

Atlantic hurricanes are a major hazard to life and property, and a topic of intense scientific interest. Historical changes in observing practices limit the utility of century-scale records of Atlantic major hurricane frequency. To evaluate past changes in frequency, we have here developed a homogenization method for Atlantic hurricane and major hurricane frequency over 1851–2019. We find that recorded century-scale increases in Atlantic hurricane and major hurricane frequency, and associated decrease in USA hurricanes strike fraction, are consistent with changes in observing practices and not likely a true climate trend. After homogenization, increases in basin-wide hurricane and major hurricane activity since the 1970s are not part of a century-scale increase, but a recovery from a deep minimum in the 1960s–1980s. We suggest internal (e.g., Atlantic multidecadal) climate variability and aerosol-induced mid-to-late-20th century major hurricane frequency reductions have probably masked century-scale greenhouse-gas warming contributions to North Atlantic major hurricane frequency.

A comparison of the temporal evolution of hydrodynamics and inlet morphology during Tropical Storm Fay (2020)

The record-setting North Atlantic hurricane season of 2020 had 30 named storms and reinforced the need for high-resolution, small-scale data collected in the nearshore zone during storm events to characterize storm impacts on coastal settings. To address these needs, hydrodynamic and morphologic data were collected during the 2020 Atlantic hurricane season, capturing fair weather conditions and the passage of Tropical Storm Fay (July 2020) near Chincoteague Inlet, Virginia. A sector-scanning rotary sonar captured high-resolution imagery of bedform evolution and data were analyzed to relate the migration of bedforms to the concomitant hydrodynamic conditions during the storm event. During the peak of the storm on 10 July 2020, significant wave height and period in Chincoteague Inlet were 0.96 m at 9.6 s arriving from the SSW (201°). The ripple field evolved during the storm in a manner consistent with that found in Hay and Mudge (2005): irregular ripples (O 20 cm wavelength) dominated during fair weather conditions, which developed into a washed-out, flat bed state as the storm arrived. During the peak of the storm, lunate megaripples (O 1 m wavelength) formed and migrated shoreward. A substantial outflow of freshwater from Chincoteague Bay occurred for up to seven days post-storm, and sediment transported by this outflow could serve as a yet-unidentified sediment source for the rapid growth of southern Assateague Island. This outflow of freshwater dampened waves and hindered ripple field recovery for up to seven days post-storm. These extreme event datasets are critical to inform coastal flood models and management decisions, as this work recognizes an increased risk of flooding for the town of Chincoteague from even the offshore passage of tropical storms.

Atlantic Hurricane Activity Prediction: A Machine Learning Approach

Long-term hurricane predictions have been of acute interest in order to protect the community from the loss of lives, and environmental damage. Such predictions help by providing an early warning guidance for any proper precaution and planning. In this paper, we present a machine learning model capable of making good preseason-prediction of Atlantic hurricane activity. The development of this model entails a judicious and non-linear fusion of various data modalities such as sea-level pressure (SLP), sea surface temperature (SST), and wind. A Convolutional Neural Network (CNN) was utilized as a feature extractor for each data modality. This is followed by a feature level fusion to achieve a proper inference. This highly non-linear model was further shown to have the potential to make skillful predictions up to 18 months in advance.

Changes in Atlantic Major Hurricane Frequency Since the Late-19th Century

Atlantic hurricanes are a major hazard to life and property1,2,3, and a topic of intense scientific interest4,5,6. Historical changes in observing practices limit the utility of century-scale records of Atlantic major hurricane frequency7-13. To evaluate past changes in frequency, we have here developed a homogenization method for Atlantic hurricane and major hurricane frequency over 1851-2019. We find that recorded century-scale increases in Atlantic hurricane and major hurricane frequency, and associated decrease in USA hurricanes strike fraction, are consistent with changes in observing practices and not likely a true climate trend. After homogenization, increases in basin-wide hurricane and major hurricane activity since the 1970s14-15 are not part of a century-scale increase, but a recovery from a deep minimum in the 1960s-1980s. These results support the notion that internal climate variability and aerosol-induced mid-to-late-20th century major hurricane frequency reductions16-24 have probably masked century-scale greenhouse-gas warming contributions to North Atlantic major hurricane frequency.