ESSC Scientist Michael Mann and graduate student Tom Sabbatelli have released their prediction for the 2009 North Atlantic hurricane season, which starts on June 1st.
The prediction is for 11.5 +/- 3.4 total named storms, which corresponds to between 8 and 15 storms. This prediction was made using the statistical model of Sabbatelli and Mann (2007, see PDF here), including the corrections for the historical undercount of events (Mann et al., 2007, see PDF here).
The basis of this forecast is the assumption that the current relatively cool sea surface temperature (SST) anomaly (0.126 C from NOAA’s Coral Reef Watch, see SST anomaly image here) in the Main Development Region (MDR) in the North Atlantic will persist throughout the 2009 hurricane season. It also takes into account current model predictions of neutral El Nino conditions during boreal Fall/Winter 2009 (see ENSO predictions here). Climatological mean conditions are assumed for the North Atlantic Oscillation (NAO) in Fall/Winter 2009.
In 2007, Mann and Sabbatelli predicted the exact number of named storms (15) for that season (see 2007 prediction). No forecast was made in 2008.
This year’s prediction is similar to other predictions for 2009, most notably the one made by Phil Klotzbach and William Gray at Colorado State University (see CSU prediction), however, the reasoning behind the predictions differs. Mann and Sabbatelli assume that the relatively low number of storms results from relatively cool SSTs in the MDR region and not from the emergence of an El Nino event in Fall/Winter 2009.
If a substantial El Nino event were to emerge (e.g. a NINO3 anomaly of +1C), then the prediction would be even lower (9.7 +/- 3.1 named storms). By contrast, if moderate La Nina conditions persist (e.g. a NINO3 anomaly of -0.5C), then the prediction would be greater (12.5+/-3.5 named storms).
Mann, M.E., Sabbatelli, T.A., Neu, U., Evidence for a Modest Undercount Bias in Early Historical Atlantic Tropical Cyclone Counts, Geophys. Res. Lett., 34, L22707, doi:10.1029/2007GL031781, 2007.
Sabbatelli, T.A., Mann, M.E., The Influence of Climate State Variables on Atlantic Tropical Cyclone Occurrence Rates, J. Geophys. Res., 112, D17114, doi: 10.1029/2007JD008385, 2007.