470 The Role of the Subtropical Jet in Dry Season Caribbean Rainstorms

Tuesday, 8 January 2019
Hall 4 (Phoenix Convention Center - West and North Buildings)
Marshall Pfahler, Univ. at Albany, SUNY, Albany, NY; and L. Bosart

Although significant high-impact heavy rainfall events in the Caribbean are typically associated with tropical cyclones during the wet season, significant heavy rainfall events can also occur during the Caribbean dry season absent of characteristics of tropical cyclones (TCs). TCs can produce infrastructure and life-threatening conditions through flooding, mudslides, and damaging winds. The most significant Caribbean dry season rainstorms can require global aid for residents to have access to vital recovery resources. The Caribbean experiences a bimodal climate with a wet season extending from May/June-November/December and dry season outside of those months. Significant rainstorms that occur during the dry season are considered anomalous by their ability to produce rainfall totals that surpass climatological monthly mean precipitation in a relatively short duration (2-16 days). The subtropical jet plays an important role in the generation and severity of dry season rainfall events in the Caribbean. This poster will present an analysis of the synoptic-scale evolution of the subtropical jet (STJ) preceding, during, and proceeding these extreme rainfall events utilizing the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR) and Climatic Research Unit (CRU) precipitation reanalysis datasets along ERA-Interim global gridded reanalysis dataset.

The evolution and position of the STJ can enable significant Caribbean rainstorms to form. Antecedent synoptic-scale conditions such as upper tropospheric anticyclonic wave breaking (AWB) over the eastern United States, Central America, or Atlantic Ocean can provide an efficient equatorward pathway for the STJ to approach the Caribbean Sea. Simultaneous formation of a potential vorticity streamer (PVS) from the AWB can promote forcing for ascent along its equatorward flank through QG dynamics. When this forcing can become juxtaposed with deep tropical moisture, intense convection can result. In some cases, strong and persistent AWB leads to eventual fracturing of a PVS from large-scale upper tropospheric deformation. Subsequent cutoff cyclogenesis can occur from satisfaction of barotropic instability. Lowered static stability can additionally aid in generation of convection in these cases. A quantitative analysis of the role of STJ evolution and position along with the contributions of AWB and PVS formation and/or fracturing to dry season Caribbean rainstorms will be conducted. This investigation will include the development of a climatology of Caribbean rainstorms from the PERSIANN-CDR and CRU datasets. Composites of associated synoptic conditions will then be derived from the ERA-Interim dataset.

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