Appendix

Table 1. 2023 North Atlantic hurricane season analog years (1950-2022).

Table 2. 2023 North Atlantic hurricane season additional analog years (1950-2022).

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. 15-day moving average of OISSTv2.1 sea surface temperature anomaly (⁰C) time series of the Atlantic Main Development Region from March 16 to May 29, 2023, via Alex Boreham (cyclonicwx.com).

Figure 3. OISSTv2.1 North Atlantic sea surface temperature anomaly (⁰C) minus mean global sea surface temperature anomaly for May 29, 2023, via Alex Boreham (cyclonicwx.com).

Figure 4. 850-hPa mean zonal wind anomaly hovmöller diagram bounded between 5°S–5°N from March 2 to May 31, 2023, depicting a series of MJO passages and subsequent WWBs.

Figure 5. Sea surface temperature anomalies (⁰C) over all ENSO regions since June 2022 (left) listed from western-most (top) to eastern-most (bottom). Eastern equatorial Pacific 0-300 meter ocean heat content anomaly (⁰C) since June 2022 (right).

Figure 6. CPC/IRI climate model ENSO forecasts as of May 2023 with statistical climate models muted to emphasize the dynamical climate model mean.

Figure 7. Ensemble Oceanic Niño Index three-month anomaly (⁰C) averages of all analogous ENSO events and the average of these events via Eric Webb (Webb and Magi, 2021).

Figure 8. A conceptual diagram of the average characteristics of a positive Indian Ocean Dipole (climate.gov).

Figure 9. Winter (DJF) mean atmospheric motion diagram of the Global Walker Circulation.

Figure 10. Mean climatological difference between ERA5 and JRA-55 (averaged) and the NCEP/NCAR R1 for 1971-2020 climate period over each study region (via Stanfield and Ramseyer, 2022 Thesis).

Figure 11. Monthly Southern Oscillation Index time series from August 2009 to May 2023. (https://www.longpaddock.qld.gov.au/soi/)

Figure 12. HadISST reanalysis mean global sea surface temperature anomalies (⁰C) for May 1951, 1957, 1965, 1997, 2002, 2006, and 2009.