An Extratropical Pathway for the Madden-Julian Oscillation's Influence on North Atlantic Tropical Cyclones

This study investigates the combined impacts of the Madden-Julian oscillation (MJO) and extratropical an-ticyclonic Rossby wave breaking (AWB) on subseasonal Atlantic tropical cyclone (TC) activity and their physical connec-tions. Our results show that during MJO phases 2-3 (enhanced Indian Ocean convection) and 6-7 (enhanced tropical Pacific convection), there are significant changes in basinwide TC activity. The MJO and AWB collaborate to suppress ba-sinwide TC activity during phases 6-7 but not during phases 2-3. During phases 6-7, when AWB occurs, various TC met-rics including hurricanes, accumulated cyclone energy, and rapid intensification probability decrease by ;50%-80%. Simultaneously, large-scale environmental variables, like vertical wind shear, precipitable water, and sea surface tempera-tures become extremely unfavorable for TC formation and intensification, compared to periods characterized by sup-pressed AWB activity during the same MJO phases. Further investigation reveals that AWB events during phases 6-7 occur in concert with the development of a stronger anticyclone in the lower troposphere, which transports more dry, sta-ble extratropical air equatorward, and drives enhanced tropical SST cooling. As a result, individual AWB events in phases 6-7 can disturb the development of surrounding TCs to a greater extent than their phases 2-3 counterparts. The influence of the MJO on AWB over the western subtropical Atlantic can be attributed to the modulation of the convectively forced Rossby wave source over the tropical eastern Pacific. A significant number of Rossby waves initiating from this region dur-ing phases 5-6 propagate into the subtropical North Atlantic, preceding the occurrence of AWB events in phases 6-7.