Real-time Somali jet index
Plotted below is a measure of the speed of the Somali jet: the square root of twice the domain mean kinetic energy of the 850 hPa horizontal wind in the region (50 E - 70 E, 5 S - 20 N). Data is from NCEP operational analyses for the current year, and NCEP reanalysis data for the climatology.
More details on this index and the associated onset of the Indian summer monsoon can be found in Boos and Emanuel (2009, QJRMS, pdf).
questions/comments: william dot boos at berkeley dot ...