There is an 80% chance this year will be the most active Atlantic hurricane season in four years, according to forecaster Tropical Storm Risk (TSR).

TSR researchers Mark Saunders and Adam Lea are forecasting 17 named storms, nine hurricanes and four major (Category 3+) hurricanes between the months of June and November – a notable increase on previous predictions.

The change in the forecast is mainly due to negative trending of the North Atlantic Oscillation, which tends to produce warmer sea surface temperatures during the peak development months of August and September.

La Nina is also likely to develop during this time, which will lead to lower trade winds and lower vertical wind shear in the main development regions.

Current forecasts for trade winds in those regions are weaker than normal, while slightly warmer than normal sea surface temperatures are anticipated.

Both of these factors lead to increased cyclogenesis – the development or strengthening of cyclonic circulation in the atmosphere.

The full report is available here.

The next forecast update will be in late July or early August.