Appendix

Table 1. 2021 North Atlantic hurricane season analog years (1950-2020).

Figure 1. (From Chiang & Vimont 2004) Spatial structures associated with the Pacific (left) and Atlantic (right) Meridional Modes. The top panels show the regression of SST (shading) and 10m wind (vectors) onto the (a) Pacific and (b) Atlantic Meridional Mode SST time series (the SST expansion coefficient from Maximum Covariance Analysis). The bottom panels show the regression of precipitation onto the (c) Pacific and (d) Atlantic Meridional Modes.

Figure 2. NCEP/NCAR reanalysis mean sea surface temperature anomalies for the North Atlantic (0⁰-60⁰N, 0⁰-120⁰W) for May 1 to May 29, 2021.

Figure 3. NCEP/NCAR reanalysis mean 850mb zonal wind anomalies for the North Atlantic (0⁰-60⁰N, 0⁰-120⁰W) for March 1 to May 29, 2021 (approximation for MAM 2021).

Figure 4. NCEP/NCAR reanalysis mean 850mb zonal wind anomalies for the North Atlantic (0⁰-60⁰N, 0⁰-120⁰W) for MAM (left) and ASO (right) 1950, 1955, 1961, 1964, and 1966.

Figure 5. NOAA Pacific Marine Environmental Laboratory five-day heat content and SST anomalies (2⁰S-2⁰N, 145⁰E-95⁰W) from May 1, 2021 to May 31, 2021.

Figure 6. North American Multi-Model Ensemble (NMME) and International Multi-Model Ensemble (IMME) amplitude-corrected Niño 3.4 forecasts valid May 2021 through Fall 2021.

Figure 7. NCEP/NCAR reanalysis March-April mean precipitable water for the African Sahel region from 1948-2021.

Figure 8. Winter (DJF) mean atmospheric motion diagram of the Global Walker Circulation.

Figure 9. NCEP/NCAR reanalysis mean of 0.2101 sigma velocity potential from January 2017 to December 2019.

Figure 10. NCEP/NCAR reanalysis mean of 0.2101 sigma velocity potential from March 1 to May 29, 2021.