Precipitation Distribution Associated with Landfalling Tropical Cyclones over the Eastern United States

Abstract

Tropical cyclones (TCs) making landfall over the United States are examined by separating those associated with precipitation predominantly left of their tracks from those with the same to the right of their tracks. Composites of atmospheric variables for these two TC categories are performed and analyzed using potential vorticity (PV) and quasigeostrophic (QG) frameworks. Dynamical signatures are retrieved from these composites to help understand the evolution of precipitation in these storms. Results indicate that a left of track precipitation distribution (e.g., Floyd 1999) is characteristic of TCs undergoing extratropical transition (ET). In these cases, a positively tilted midlatitude trough approaches the TC from the northwest, shifting precipitation to the north-northwest of the TC. Potential vorticity redistribution through diabatic heating leads to enhanced ridging over and downstream of the TC, resulting in an increase in the cyclonic advection of vorticity by the thermal wind over the transitioning TC. A right of track precipitation distribution is characteristic of TCs interacting with a downstream ridge (e.g., David 1979). When the downstream ridge amplifies in response to TC-induced diabatic heating ahead of a weak midlatitude trough, the PV gradient between the TC and the downstream ridge is accentuated, producing a region of enhanced positive PV advection (and cyclonic vorticity advection by the thermal wind) over the TC. The diabatic enhancement of the downstream ridge is instrumental in the redistribution of precipitation about the transitioning TCs in both cases and poses a significant forecast challenge.

Comparing the Spatial Patterns of Rainfall and Atmospheric Moisture among Tropical Cyclones Having a Track Similar to Hurricane Irene (2011)

“…A comparison with totals greater than 150 mm contained in the NHC report [3] showed that the UPD tended to underestimate storm total rainfall by 50-75 mm, but the locations of the higher amounts were consistent. Underestimation of rainfall by this interpolated and gridded dataset is expected and has been documented for TCs by Atallah et al [6], yet these results suggest that the locations of the highest rainfall totals should be comparable across storms.…”

“…This limits the ability to investigate rainfall produced on the right side of the storm's track. Previous studies have used this dataset to examine rainfall from TCs [6,41], supporting its use in the current study. The fact that strong winds near the TC's center causes undercatch in rain gauges leading to lower rainfall totals should also be noted [42][43][44].…”

“…Two main advantages of utilizing this dataset are (1) its complete spatial and temporal coverage over U.S. land areas beginning in 1948 and (2) that a uniform interpolation method, quality control checks, and error corrections were applied to the entire dataset. The two main limitations of this dataset are that (1) rainfall totals are averaged over grid cells approximating 770 km 2 so that values are underestimated, particularly for regions receiving high rainfall amounts [6] and (2) data are only available over land areas so that rainfall occurring offshore cannot be analyzed. This limits the ability to investigate rainfall produced on the right side of the storm's track.…”

“…Many TCs tracking over the northeastern U.S. have produced heavy rainfall that caused flooding [5][6][7][8][9]. When passing through this region, TCs can become restructured from a warm-core to a cold-core cyclone through the process of extratropical transition (ET) [8].…”

Kinetic Energy Budget of a Tropical Cyclone

“…The bulk upscale influences of convection in baroclinic cyclones obviously force the downstream synoptic scale and instant mesoscale environment. This includes: enhanced differential cyclonic vorticity advection ahead of weak upstream troughs resulting from convection-generated enhanced downstream ridging and jet development with landfalling and recurving tropical cyclones [23] [24]; vorticity buildup and merger in vortical hot convective towers throughout initial tropical cyclogenesis [25]; and mesoscale ridging in the upper troposphere ahead of convection linked with mesoscale convective vortices [26].…”