The spatial patterns of rainfall produced by Hurricane Irene (2011) and other tropical cyclones with similar tracks

During the 2011 hurricane season, Hurricane Irene produced heavy rainfall that caused flooding in multiple locations from North Carolina to Maine. TCs with tracks over the U.S. similar to that of Irene are typically undergoing extratropical transition during which rain fields broaden in areal extent and frontal boundaries can enhance rainfall west of the storm track. This study explored the spatial patterns of rainfall produced by Irene and other TCs with similar tracks. Using a Geographic Information System (GIS), Irene's track was buffered by 200 km, and TCs from previous seasons featuring a long track segment within this buffer with similar orientation were identified. Daily rainfall totals were obtained from the National Centers for Environmental Prediction–Climate Prediction Center Unified Precipitation Dataset, with gridded data at a 0.25° spatial resolution available beginning in 1948. Eleven of the 25 similar TC tracks occurred post-1948. Storm-total rainfall values for all 12 TCs were calculated utilizing the cell statistics tool in ArcGIS. The distance and angle between the nearest point on the storm track and the centroid of each grid cell was also calculated. The highest 10% of rainfall totals left of track were analyzed further. Measures of central tendency and dispersion were calculated and Spearman's rank correlations explored associations between the locations of high rainfall totals, distance to track, and latitude. The highest rainfall accumulating at each cell and the storm producing it was also determined. The rainfall patterns and totals most similar to Irene were produced by Hurricane Floyd (1999). The median value of Floyd's highest rainfall cells was 256 mm, which is 22 mm greater than Irene. The highest rainfall produced by Irene had a median of 56 mm above that of Hurricanes Donna (1960) and Gloria (1985). The median distance between high rainfall locations and storm track was 87 km for Floyd, which is within 10 km of that of Irene. Floyd produced the highest rainfall of the 12 TCs over 24% of the study region. Statistically significant negative correlations between high rainfall locations and distance to track and latitude occurred for Floyd and Carol (1954) suggesting that their rain fields broadened and produced less rain as the storm moved north. A strong negative correlation with latitude but insignificant correlation with distance to track for Irene and Brenda (1960) suggests that their rainfall also decreased as the storm moved north but their rain fields did not greatly shift in location relative to the storm center.