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Long range Tropical Storm forecasts

Tropical storm plots show statistics about the expected number of tropical storms and number of hurricanes/typhoons per basin over months 2-7 of the forecast period compared with climatology.   

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Time-series of tropical storm statistics on the number of hurricanes/typhoons and statistics on the accumulated cyclone energy are also available for each basin.  These show the latest forecast along with all previous forecasts/re-forecasts, and with the observed verification for previous years.  The forecasts are shown as an ensemble mean for each year (in blue), plus and minus one standard deviation (green lines).   If the forecasts were reliable, the observations would fall within this range about 70% of the time.  The time-series plots also show the correlation and Root Mean Square Error, calculated over the verified forecasts shown.  Calibration of past forecasts is always cross-validated, and uses either all other years (excluding the year being predicted), or the 10 years previous to the year predicted, depending on ocean basin.

Empirical Orthogonal Function (EOF) - based rainfall indices

Explanation of the derivation of the climagrams of rainfall indices available on Opencharts.

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In the first EOF of the South Asia - Indian Ocean region, anomalies over Indonesia and the eastern tropical Indian Ocean have opposite sign to those over South-East Asia, the Bay of Bengal and the South China Sea. This pattern strongly resembles the rainfall response to summer ENSO episodes (the sign in the figure corresponding to cold events). Rainfall anomalies in the Indian sub-continent and the adjacent seas are dominant in the second EOF for this region, which also shows rainfall anomalies over the Indian Ocean resembling the response to the Indian Ocean SST dipole. According to the regions with largest anomalies, projections on these EOFs are referred to as the Eastern Tropical Indian Ocean and the South Asian Monsoon indices.

All India Rainfall

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Index

An All India Rainfall index is defined here as a weighted average of rainfall anomalies in the region 5 - 30 N, 70 - 90 E. The weights are proportional to the fraction of low-altitude land in each 2.5-deg. box of the GPCP grid. This fraction is computed from the full-resolution land-sea mask and surface topography of the ERA-Interim dataset, low-altitude points being defined as grid points with surface height less than 1000 m. The low-altitude criterion excludes points corresponding to the mountain regions of Nepal and Tibet. The land fraction is additionally set to 0 over Sri Lanka, values less 0.2 are discarded, and weights are finally normalized to have area average = 1.

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