The precursors in the Intra‐Americas Seas to seasonal climate variations over North America

In this paper, we show from observations that the Intra-American Seas precursor as characterized by the onset of the Atlantic Warm Pool (AWP; defined by the area enclosed by 28.5 degrees C isotherm in the tropical Atlantic Ocean) has discernible impact on the boreal summer and fall seasonal climate variations over North America, a season and a region well known for relatively poor seasonal predictability. The onset of the AWP season is objectively defined as the day when the daily anomaly of the AWP area, west of 50 degrees W, and north of the equator exceeds its climatological annual mean value. We show that early (late) onset of AWP is associated with following August-September-October (ASO) deficit (excess) seasonal rainfall anomalies over southern Mississippi valley extending to the Midwest US east of Iowa. On the other hand, Central America and the Caribbean region exhibit enhanced (decreased) ASO seasonal mean rainfall during an early (late) onset of AWP. We also find that early (late) onset of the AWP is associated with early (late) onset and early (late) demise of the rainy season over Mesoamerica. This relationship also leads to association of early (late) onset of AWP with increased (shortened) length of the rainy season over Mesoamerica. These teleconnections are dictated by the modulation of the low-level flow and moisture flux convergence associated with the varying development of the AWP. Similarly, we find that early (late) onset years of the AWP are associated with a more active (inactive) seasonal Atlantic tropical cyclone activity. These teleconnections are sustained from the fact that the AWP onset date variations are found to be a precursor to the seasonal AWP size variations.