Discussion: The Climate Impact Company constructed analog (CIC-CA) forecast is based primarily on the ENSO forecast and SSTA regime in the MDR. ENSO and the North Atlantic basin SSTA regimes have long-term cycles. During the mid-to-late 1990’s, ENSO flipped from the warm cycle to the cool cycle as El Nino episodes are suppressed and La Nina events more frequent (Fig. 1). At the same time, in the North Atlantic basin, the Atlantic Multi-decadal oscillation (AMO) shifted from the cool to warm cycle in which the North Atlantic is warmer than normal most of the time (Fig. 2). In the MDR, the tropical North Atlantic (TNA) index also shifted to the warm phase and is causal to the increased number of hurricanes of recent decades (Fig. 3). Since a more persistent presence of La Nina and warmer than normal SSTA in the North Atlantic favors increased tropical cyclone activity, the climatology of seasonal activity has increased (Fig. 4). The Climate Impact Company seasonal forecast of North Atlantic basin tropical cyclone activity is primarily reliant on analog years within the current cool ENSO/warm AMO climate with similar ENSO/AMO (and TNA) characteristics. The ENSO climatology according to ENSO phase is also provided (Fig. 5).
Fig. 1: The 1950-2023 monthly plot of the El Nino southern oscillation phase.
Fig. 2: The 1950-2023 monthly plot of the Atlantic multi-decadal oscillation.
Fig. 3: The 1950-2023 monthly plot of the tropical North Atlantic index.
Fig. 4: Climate Impact Company climatology of North Atlantic basin tropical cyclone activity.
Fig. 5: Climate Impact Company climatology of North Atlantic basin tropical cyclone activity according to ENSO phase.