Early Detection of Hurricane
The top figure shows rotation of surface winds revealed by QuikSCAT data in the Atlantic, on August 23, 1999. The bottom figure displays the GOES image, used by the National Hurricane Center (NHC) to detect tropical cyclones, over the same area on the same day; there was no apparent indication of closed circulation. It was only 35 hours later that the National Hurricane Center (NHC) was able to identify the rotating wind system as tropical storm Emily.
NHC identifies tropical depression by looking for organized surface circulation, mainly derived from cloud images of weather satellites. Since high level clouds may obscure lower level cloud motions and delay detection of rotation, an attempt was made to see if the vorticity might first be detected in the surface winds seen by QuikSCAT. Eleven tropical depressions were identified by NHC in 1999 after the launch of QuikSCAT. QuikSCAT data in areas upstream and before their identification by NHC were examined for rotation, and it was found that QuikSCAT data can identify tropical depressions up to 46 ahead of NHC. No false alarm was found. A closed surface circulation with westerly winds stronger than 10 m/s, south of the center, was the criteria used in this study, and used at NHC, to identify tropical depression.
The figure and further discussion can be found in the paper by Katsaros, K.B., E.B.Forde, P. Chang, and W.T. Liu, 2001: QuikSCAT facilitates early identification of tropical deprssions in 1999 hurricane season. Geophys. Res. Lett., 28,1043-1046.