Abstract
<p>Here we investigate tropical cyclone (TC) activity and intensity within a 100km radius of Bermuda between 1955 and 2019. Our results show a more easterly genesis over time and significant increasing trends in tropical cyclone intensity (maximum wind speed (Vmax)) with a decadal Vmax median value increase of 30kts from 33 to 63kts, together with significant increasing August, September, October (ASO) sea surface temperature (SST) of 1.1°C (0.17 °C per decade)  and ocean temperature between 0.5–0.7°C (0.08-0.1°C per decade)  in the depth range 0-300m. The strongest correlation is found between TC intensity and ocean temperature averaged through the top 50m ocean layer (T<sub>50m</sub>) r=0.37 (p<0.01). </p><p>We show how tropical cyclone potential intensity estimates are closer to actual intensity by using T<sub>50m</sub> opposed to SST using the Bermuda Atlantic Timeseries Hydrostation S dataset. We modify the widely used sea surface temperature potential intensity index by using T<sub>50m</sub> to provide a closer estimate of the observed minimum sea level pressure (MSLP), and associated Vmax than by using SST, creating a T<sub>50m </sub>potential intensity (T<sub>50m</sub>_PI) index. The average MSLP difference is reduced by 12mb and proportional to the SST/ T<sub>50m </sub>temperature difference. We also suggest the index could be used over a wider area of the subtropical/tropical Atlantic where there is a shallow mixed layer depth. Finally, we outline the TC wind-pressure relationship observed for the subtropical Atlantic around Bermuda, explaining 77% of the variance, which may prove useful for future prediction.</p><p>(Environmental Research Letters, 2020, in revision)</p><p> </p><p> </p>
Highlights
Introduction ceIn September 2019 Hurricane Humberto was the latest Category 3 hurricane to impactBermuda, with 100 knot winds and causing power outage to over 80% of the island, and there have been several other intense hurricanes impacting the island in the recent past: Fabian (2003), Gonzalo (2014), Nicole (2016) and Paulette (2020).Observed Atlantic hurricane frequency has been found to correlate with the variability of sea surface temperatures on seasonal (Hallam et al, 2019) to multidecadal timescales, as measured by the Atlantic Multi-decadal Variability (AMV)index (Goldenberg et al, 2001), which is the North Atlantic area-averaged (0–60°N, 0– AcAUTHOR SUBMITTED MANUSCRIPT - ERL-109570.R2an us cri pt 80°W) Sea Surface Temperature Anomaly (SSTA)
The different genesis pattern between the 2 periods is consistent with the all Atlantic track trend which shows a 62% increase in tropical cyclone (TC) genesis off Africa (10-20N, 0-30W) in the period 2000-2019 compared to 1980-1999 (Fig. 1(iv) and (v))
In this study we have reviewed TCs in the Bermuda area from 1955 -2019 and highlighted the more easterly genesis of tracks in the period 2000-2019 compared to
Summary
In September 2019 Hurricane Humberto was the latest Category 3 hurricane to impact. Bermuda, with 100 knot winds and causing power outage to over 80% of the island, and there have been several other intense hurricanes impacting the island in the recent past: Fabian (2003), Gonzalo (2014), Nicole (2016) and Paulette (2020). TC maximum potential intensity based on SST, which provides an estimate of the theoretical upper limit of TC intensity, was calculated based on the method and code (http://emanuel.mit.edu/products) developed by Emanuel (1999) which uses the energy cycle of the storm to estimate the maximum possible surface wind speed and the minimum central pressure. It can be written in convective available potential energy (CAPE) terms (Emanuel, 1994, Bister and Emanuel, 2002). For comparison to the potential intensity estimates, actual V and minimum central pressure of the TC were taken from the HURDAT2 data
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