Fujiwhara Effect on Track Deflection Associated with Hurricane Sandy (2012) Before Landfalling on the US East Coast

The Interim Re-Analysis (ERA) data of the European Centre for Medium-Range Weather Forecasts was analyzed to help understand the inland (northwestward) track of Hurricane Sandy (2012). We found the following three stages are essential in determining Sandy's inland movement: (1) During 10/28/12Z – 10/29/00Z, a northwestward steering flow was formed in upper troposphere by the interaction of a developing baroclinic wave and Sandy, which led to the inland (northwestward) movement of Sandy starting around 10/29/00Z, (2) During 10/29/00Z – 10/29/18Z, Sandy's vortex and the cyclonic vortex embedded in the inland middle- and upper-level trough interacted and move around each other cyclonically while the trough deepened toward southeast, and (3) During 10/29/18Z – 10/30/00Z, Sandy began to merge with the inland trough to form a cut-off low in the middle-troposphere and transitioned to extratropical cyclone while landfell around 10/29/2330Z. Combination of the above three processes led to the inland turning and movement during the period of 10/29/00Z and 10/30/00Z. We hypothesize that the 2nd stage was controlled by the Fujiwhara effect. This hypothesis was tested using an Advanced Research WRF (ARW) simulation initialized with the ERA data from the 10/26/00Z – 10/31/00Z. The domain resolution was 12 km, had 392 grid points in both E-W and N-S centered about 32N – 75W, and utilized 60 vertical levels. The three stages that were identified through the ERA analysis were confirmed through the simulation outputs. Furthermore, as hypothesized the Fujiwhara effect was the dominant mechanism turning Sandy inland during the second stage. The length of the three stages was shorter than that identified by the ERA analysis due higher temporal resolution in simulation outputs. In order to test the Fujiwhara effect, we performed additional numerical experiments in which we removed Sandy from the domain to determine to what degree Sandy influenced the deepening of the trough and its contribution to the Fujiwhara effect. Sandy was weakened significantly using the bogusing programs included in the ARW modeling system. In simulations with Sandy removed, the trough does not steepen as fast as that with Sandy. Furthermore, the closed circulation associated with the trough forms several hours later than the control simulation with Sandy.