Colorado State University scientists Philip Klotzbach and William Gray confirmed their earlier predictions for an active Atlantic basin hurricane season Tuesday.
The scientists are predicting 15 named storms, eight hurricanes and four major hurricanes with winds of at least 111 mph. The forecast is unchanged from their 9 April forecast. An average hurricane season has 11 named storms and six hurricanes, two of which become major hurricanes.
The forecast also predicts an above-average risk of a major hurricane making landfall in the Caribbean.
One potential problem with their forecast is whether there will be a neutral ENSO condition or an El Niño in the Pacific Ocean. El Niño conditions, which are caused by a warming of the waters of the Pacific, have historically inhibited hurricane formation in the Atlantic basin because they create upper atmospheric conditions that cause wind shear, which can prevent hurricanes from forming. Conversely, neutral ENSO condition in the Pacific have historically allowed for active hurricane seasons in the Atlantic basin.
‘The primary concern with our current seasonal forecast numbers is the continued ocean surface warming in the eastern and central tropical Pacific,’ Klotzbach and Gray’s report states, adding that an El Niño could develop this summer and fall.
The ENSO conditions during the peak Atlantic Basin hurricane season are the key.
‘The big question is whether this current observed warming will continue through this year’s hurricane season,’ the CSU report states. ‘At this time, it appears unlikely that ENSO will transition to warm conditions by the August-October period. None of the statistical models and only one of the dynamical models currently predicts an El Niño event over the [August-October] period.’
The CSU forecast is based on a statistical prediction scheme that uses 58 years of past data.
‘We have found that using two spring predictors and our early April hind-cast, we can obtain early June hind-casts that show considerable skill over the period from 1950-2007,’ their report states.
Klotzbach and Gray have taken some criticism in recent years for badly under-forecasting 2005’s record-setting year and then over-forecasting the 2006 hurricane season.
They say they issue the seasonal hurricane forecasts because there is ‘inherent curiosity among the general public about how active or inactive the coming season is likely to be’.
‘However, one must realise that these are statistical forecasts, which will fail in some years,’ they state. ‘We find we learn a lot from our forecast errors.’
The US National Oceanic and Atmospheric Administration and the UK-based Tropical Storm Risk have also predicted above average hurricane seasons in the Atlantic Basin this year.
The Atlantic Basin hurricane season began Sunday and runs through 30 November, with the peak historic activity occurring in the second week of September. There has already been one named storm this year, when Tropical Storm Arthur formed in the western Caribbean Sea last week. The storm killed four people in Belize and left two missing.