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patterns such as the Loop Current along the WFS, continuing as the Florida Current (FC) in
the Straits of Florida (southern branch along the Florida Keys and northern branch along
the EFS). The Loop Current/Florida Current system around South Florida constitutes the
evolution of the Gulf Stream over the region [25], carrying warm Caribbean waters toward
the Atlantic Ocean. The meandering of the FC through the Straits of Florida is associated
with mesoscale eddy activity to the north (along the Florida Keys; [26]) and the south
(along the Cuban coast, [27,28]). The cyclonic eddies [26,29] and the proximity of the FC to
the southern WFS [30] affect the local circulation and SST distribution over the southern
WFS and the Florida Keys. The Loop Current evolution and the accompanying Loop
Current Frontal Eddies [31,32] over the shelf break of the WFS, together with the prevailing
atmospheric conditions (winds and heat fluxes), determine the SST variability over the
shelf [33–35]. Upwelling and downwelling processes under favorable wind conditions
may also alter the surface temperature levels along the western [36,37] and eastern [38,39]
Florida coasts. South Florida has a tropical climate, characterized by a wet summer season
and a dry one from mid-fall through late spring [40]. Hurricane-induced winds that may
occur during tropical storm events (typically from June to November) may control the
ocean circulation, the vertical mixing and the SST distribution of the affected coastal regions.
The frequency of hurricanes has been rather constant through time, but there is evidence of
upward trends in the intensity of the strongest hurricanes, showing increasing trends of
the wind speed around 13 Β± 6 m/s/century [41].
In this study, we focus on the relationship between MHW events and the spatial and
temporal SST variability over the South Florida coastal region during the most recent
40-year period (1982–2021). We have adopted a methodology that uses high-resolution
(~5 km) satellite observations, field observations, meteorological data, and numerical hydrodynamic simulations. We discuss the interannual variability and the spatial differences
Water 2022, 14, 3840 4 of 28
between coastal regions of South Florida with high environmental interest (e.g., coral
reefs, seagrass beds, mangrove forests) or extensive urban infrastructure and population
(e.g., Miami metropolitan area). The main motivation of the study is to contribute to the
understanding of climate change impacts around the coastal areas of South Florida, by
examining the increasing temperature trends (SST) in the surrounding ocean waters and
for the first time, the resulting MHWs that can impact the marine and urban environments.
The goal is to identify the SST differences between the South Florida sub-regions and the
respective coastal waters during the last four decades. This can be potentially useful to the
research on the implications between physical and biochemical properties. We will also
evaluate the environmental met-ocean factors that are responsible for the interannual SST
variability and trends of each coastal area, focusing on the formation of MHWs and their
interannual variability over this region. The related along-shore variability and interannual
trends along the entire coastal region, which is of great ecological and socioeconomic
importance (especially due to coral reef ecosystems, [42,43]), will be also discussed.
More information about the methods and data are given in Section 2. Section 3 presents
the main results concerning the SST variability and trends, and the formation of MHWs.
Section 4 discusses the atmospheric and ocean effects on temperature distribution. Finally,
a summary with concluding remarks is presented in Section 5.
2. Materials and Methods
The data used in the current study consist of satellite observations (SST), atmospheric
modeling data, ocean field observations, and simulated ocean fields covering parts or the
entire study period (1 January 1982 to 31 December 2021). A summary of the data and their
main characteristics is presented in Table 1.
Table 1. Main characteristics of observational and modeling data used in the study (parameter, type,
spatial and temporal resolution, area coverage, dataset source).
Parameter Type Res. Step Period Area Source
SST Satellite 0.05β—¦ Daily 1982–2021 Florida Straits, South
Florida, and Florida Keys
Copernicus
System
Air temperature
(2 m)
ECMWF
Reanalysis
(ERA5)
0.25β—¦ Hourly 1982–2021 Florida Straits, South
Florida, and Florida Keys
Copernicus
System
Wind Components
(10 m)
ECMWF
Reanalysis
(ERA5)
0.25β—¦ Hourly 1982–2021 Florida Straits, South
Florida, and Florida Keys
Copernicus
System
Radiations
(Shortwave,
Longwave, Sensible,
Latent)
ECMWF
Reanalysis
(ERA5)
0.25β—¦ Hourly 1982–2021 Florida Straits, South
Florida, and Florida Keys
Copernicus
System
SST In Situ Buoy Hourly
2005
2005–2010
2005–2007
Key West
Key Largo
Biscayne Bay
NOAA/NDBC
Air Temperature In Situ Buoy Hourly 2012–2020 Biscayne Bay NOAA/NDBC
Temperature and
Currents
Hydrodynamic
Modeling 0.01β—¦ 6-hourly 2012–2020 Florida Straits, South
Florida, and Florida Keys
University of
Miami